draft-ietf-tcpm-converters-19.txt   rfc8803.txt 
TCPM Working Group O. Bonaventure, Ed. Internet Engineering Task Force (IETF) O. Bonaventure, Ed.
Internet-Draft Tessares Request for Comments: 8803 Tessares
Intended status: Experimental M. Boucadair, Ed. Category: Experimental M. Boucadair, Ed.
Expires: September 22, 2020 Orange ISSN: 2070-1721 Orange
S. Gundavelli S. Gundavelli
Cisco Cisco
S. Seo S. Seo
Korea Telecom Korea Telecom
B. Hesmans B. Hesmans
Tessares Tessares
March 21, 2020 July 2020
0-RTT TCP Convert Protocol 0-RTT TCP Convert Protocol
draft-ietf-tcpm-converters-19
Abstract Abstract
This document specifies an application proxy, called Transport This document specifies an application proxy, called Transport
Converter, to assist the deployment of TCP extensions such as Converter, to assist the deployment of TCP extensions such as
Multipath TCP. A Transport Converter may provide conversion service Multipath TCP. A Transport Converter may provide conversion service
for one or more TCP extensions. The conversion service is provided for one or more TCP extensions. The conversion service is provided
by means of the TCP Convert Protocol (Convert). by means of the 0-RTT TCP Convert Protocol (Convert).
This protocol provides 0-RTT (Zero Round-Trip Time) conversion This protocol provides 0-RTT (Zero Round-Trip Time) conversion
service since no extra delay is induced by the protocol compared to service since no extra delay is induced by the protocol compared to
connections that are not proxied. Also, the Convert Protocol does connections that are not proxied. Also, the Convert Protocol does
not require any encapsulation (no tunnels, whatsoever). not require any encapsulation (no tunnels whatsoever).
This specification assumes an explicit model, where the Transport This specification assumes an explicit model, where the Transport
Converter is explicitly configured on hosts. As a sample Converter is explicitly configured on hosts. As a sample
applicability use case, this document specifies how the Convert applicability use case, this document specifies how the Convert
Protocol applies for Multipath TCP. Protocol applies for Multipath TCP.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This document is not an Internet Standards Track specification; it is
provisions of BCP 78 and BCP 79. published for examination, experimental implementation, and
evaluation.
Internet-Drafts are working documents of the Internet Engineering This document defines an Experimental Protocol for the Internet
Task Force (IETF). Note that other groups may also distribute community. This document is a product of the Internet Engineering
working documents as Internet-Drafts. The list of current Internet- Task Force (IETF). It represents the consensus of the IETF
Drafts is at https://datatracker.ietf.org/drafts/current/. community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are candidates for any level of
Internet Standard; see Section 2 of RFC 7841.
Internet-Drafts are draft documents valid for a maximum of six months Information about the current status of this document, any errata,
and may be updated, replaced, or obsoleted by other documents at any and how to provide feedback on it may be obtained at
time. It is inappropriate to use Internet-Drafts as reference https://www.rfc-editor.org/info/rfc8803.
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 22, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction
1.1. The Problem . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. The Problem
1.2. Network-Assisted Connections: The Rationale . . . . . . . 4 1.2. Network-Assisted Connections: The Rationale
1.3. Applicability Scope . . . . . . . . . . . . . . . . . . . 6 1.3. Applicability Scope
2. Differences with SOCKSv5 . . . . . . . . . . . . . . . . . . 6 2. Conventions and Definitions
3. Conventions and Definitions . . . . . . . . . . . . . . . . . 8 3. Differences with SOCKSv5
4. Architecture & Behaviors . . . . . . . . . . . . . . . . . . 9 4. Architecture and Behaviors
4.1. Functional Elements . . . . . . . . . . . . . . . . . . . 9 4.1. Functional Elements
4.2. Theory of Operation . . . . . . . . . . . . . . . . . . . 11 4.2. Theory of Operation
4.3. Data Processing at the Transport Converter . . . . . . . 14 4.3. Data Processing at the Transport Converter
4.4. Address Preservation vs. Address Sharing . . . . . . . . 16 4.4. Address Preservation vs. Address Sharing
4.4.1. Address Preservation . . . . . . . . . . . . . . . . 16 4.4.1. Address Preservation
4.4.2. Address/Prefix Sharing . . . . . . . . . . . . . . . 17 4.4.2. Address/Prefix Sharing
5. Sample Examples . . . . . . . . . . . . . . . . . . . . . . . 18 5. Sample Examples
5.1. Outgoing Converter-Assisted Multipath TCP Connections . . 18 5.1. Outgoing Converter-Assisted Multipath TCP Connections
5.2. Incoming Converter-Assisted Multipath TCP Connection . . 20 5.2. Incoming Converter-Assisted Multipath TCP Connection
6. The Convert Protocol (Convert) . . . . . . . . . . . . . . . 21 6. The Convert Protocol (Convert)
6.1. The Convert Fixed Header . . . . . . . . . . . . . . . . 22 6.1. The Convert Fixed Header
6.2. Convert TLVs . . . . . . . . . . . . . . . . . . . . . . 23 6.2. Convert TLVs
6.2.1. Generic Convert TLV Format . . . . . . . . . . . . . 23 6.2.1. Generic Convert TLV Format
6.2.2. Summary of Supported Convert TLVs . . . . . . . . . . 24 6.2.2. Summary of Supported Convert TLVs
6.2.3. The Info TLV . . . . . . . . . . . . . . . . . . . . 25 6.2.3. The Info TLV
6.2.4. Supported TCP Extensions TLV . . . . . . . . . . . . 25 6.2.4. Supported TCP Extensions TLV
6.2.5. Connect TLV . . . . . . . . . . . . . . . . . . . . . 26 6.2.5. Connect TLV
6.2.6. Extended TCP Header TLV . . . . . . . . . . . . . . . 28 6.2.6. Extended TCP Header TLV
6.2.7. The Cookie TLV . . . . . . . . . . . . . . . . . . . 29 6.2.7. The Cookie TLV
6.2.8. Error TLV . . . . . . . . . . . . . . . . . . . . . . 30 6.2.8. Error TLV
7. Compatibility of Specific TCP Options with the Conversion 7. Compatibility of Specific TCP Options with the Conversion
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Service
7.1. Base TCP Options
7.1. Base TCP Options . . . . . . . . . . . . . . . . . . . . 33 7.2. Window Scale (WS)
7.2. Window Scale (WS) . . . . . . . . . . . . . . . . . . . . 34 7.3. Selective Acknowledgments
7.3. Selective Acknowledgments . . . . . . . . . . . . . . . . 34 7.4. Timestamp
7.4. Timestamp . . . . . . . . . . . . . . . . . . . . . . . . 35 7.5. Multipath TCP
7.5. Multipath TCP . . . . . . . . . . . . . . . . . . . . . . 35 7.6. TCP Fast Open
7.6. TCP Fast Open . . . . . . . . . . . . . . . . . . . . . . 35 7.7. TCP-AO
7.7. TCP-AO . . . . . . . . . . . . . . . . . . . . . . . . . 36 8. Interactions with Middleboxes
8. Interactions with Middleboxes . . . . . . . . . . . . . . . . 36 9. Security Considerations
9. Security Considerations . . . . . . . . . . . . . . . . . . . 37 9.1. Privacy & Ingress Filtering
9.1. Privacy & Ingress Filtering . . . . . . . . . . . . . . . 37 9.2. Authentication and Authorization Considerations
9.2. Authentication and Authorization Considerations . . . . . 38 9.3. Denial of Service
9.3. Denial of Service . . . . . . . . . . . . . . . . . . . . 40 9.4. Traffic Theft
9.4. Traffic Theft . . . . . . . . . . . . . . . . . . . . . . 40 9.5. Logging
9.5. Logging . . . . . . . . . . . . . . . . . . . . . . . . . 40 10. IANA Considerations
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40 10.1. Convert Service Name
10.1. Convert Service Name . . . . . . . . . . . . . . . . . . 40 10.2. The Convert Protocol (Convert) Parameters
10.2. The Convert Protocol (Convert) Parameters . . . . . . . 41 10.2.1. Convert Versions
10.2.1. Convert Versions . . . . . . . . . . . . . . . . . . 41 10.2.2. Convert TLVs
10.2.2. Convert TLVs . . . . . . . . . . . . . . . . . . . . 42 10.2.3. Convert Error Messages
10.2.3. Convert Error Messages . . . . . . . . . . . . . . . 42 11. References
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 43 11.1. Normative References
11.1. Normative References . . . . . . . . . . . . . . . . . . 43 11.2. Informative References
11.2. Informative References . . . . . . . . . . . . . . . . . 45 Appendix A. Example Socket API Changes to Support the 0-RTT TCP
Appendix A. Example Socket API Changes to Support the 0-RTT Convert Protocol
Convert Protocol . . . . . . . . . . . . . . . . . . 48 A.1. Active Open (Client Side)
A.1. Active Open (Client Side) . . . . . . . . . . . . . . . . 48 A.2. Passive Open (Converter Side)
A.2. Passive Open (Converter Side) . . . . . . . . . . . . . . 49 Acknowledgments
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 50 Contributors
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Authors' Addresses
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52
1. Introduction 1. Introduction
1.1. The Problem 1.1. The Problem
Transport protocols like TCP evolve regularly [RFC7414]. TCP has Transport protocols like TCP evolve regularly [RFC7414]. TCP has
been improved in different ways. Some improvements such as changing been improved in different ways. Some improvements such as changing
the initial window size [RFC6928] or modifying the congestion control the initial window size [RFC6928] or modifying the congestion control
scheme can be applied independently on clients and servers. Other scheme can be applied independently on Clients and Servers. Other
improvements such as Selective Acknowledgments [RFC2018] or large improvements such as Selective Acknowledgments [RFC2018] or large
windows [RFC7323] require a new TCP option or to change the semantics windows [RFC7323] require a new TCP option or changing the semantics
of some fields in the TCP header. These modifications must be of some fields in the TCP header. These modifications must be
deployed on both clients and servers to be actually used on the deployed on both Clients and Servers to be actually used on the
Internet. Experience with the latter class of TCP extensions reveals Internet. Experience with the latter class of TCP extensions reveals
that their deployment can require many years. Fukuda reports in that their deployment can require many years. Fukuda reports in
[Fukuda2011] results of a decade of measurements showing the [Fukuda2011] results of a decade of measurements showing the
deployment of Selective Acknowledgments, Window Scale, and TCP deployment of Selective Acknowledgments, Window Scale, and TCP
Timestamps. [ANRW17] describes measurements showing that TCP Fast Timestamps. [ANRW17] describes measurements showing that TCP Fast
Open (TFO) [RFC7413] is still not widely deployed. Open (TFO) [RFC7413] is still not widely deployed.
There are some situations where the transport stack used on clients There are some situations where the transport stack used on Clients
(or servers) can be upgraded at a faster pace than the transport (or Servers) can be upgraded at a faster pace than the transport
stack running on servers (or clients). In those situations, clients stack running on Servers (or Clients). In those situations, Clients
would typically want to benefit from the features of an improved (or Servers) would typically want to benefit from the features of an
transport protocol even if the servers have not yet been upgraded and improved transport protocol even if the Servers (or Clients) have not
conversely. Some assistance from the network to make use of these yet been upgraded. Some assistance from the network to make use of
features is valuable. For example, Performance Enhancing Proxies these features is valuable. For example, Performance Enhancing
[RFC3135], and other service functions have been deployed as Proxies [RFC3135] and other service functions have been deployed as
solutions to improve TCP performance over links with specific solutions to improve TCP performance over links with specific
characteristics. characteristics.
Recent examples of TCP extensions include Multipath TCP (MPTCP) Recent examples of TCP extensions include Multipath TCP (MPTCP)
[RFC6824] or TCPINC [RFC8548]. Those extensions provide features [RFC8684] or tcpcrypt [RFC8548]. Those extensions provide features
that are interesting for clients such as wireless devices. With that are interesting for Clients such as wireless devices. With
Multipath TCP, those devices could seamlessly use Wireless Local Area Multipath TCP, those devices could seamlessly use Wireless Local Area
Network (WLAN) and cellular networks, for bonding purposes, faster Network (WLAN) and cellular networks for bonding purposes, faster
hand-overs, or better resiliency. Unfortunately, deploying those hand-overs, or better resiliency. Unfortunately, deploying those
extensions on both a wide range of clients and servers remains extensions on both a wide range of Clients and Servers remains
difficult. difficult.
More recently, 5G bonding experimentation has been conducted into More recently, 5G bonding experimentation has been conducted into
global range of the incumbent 4G (LTE) connectivity using newly global range of the incumbent 4G (LTE) connectivity using newly
devised clients and a Multipath TCP proxy. Even if the 5G and the 4G devised Clients and a Multipath TCP proxy. Even if the 5G and 4G
bonding (that relies upon Multipath TCP) increases the bandwidth, it bonding (that relies upon Multipath TCP) increases the bandwidth, it
is as well crucial to minimize latency for all the way between is also crucial to minimize latency entirely between end hosts
endhosts regardless of whether intermediate nodes are inside or regardless of whether intermediate nodes are inside or outside of the
outside of the mobile core. In order to handle Ultra Reliable Low mobile core. In order to handle Ultra-Reliable Low Latency
Latency Communication (URLLC) for the next generation mobile network, Communication (URLLC) for the next-generation mobile network,
Multipath TCP and its proxy mechanism such as the one used to provide Multipath TCP and its proxy mechanism such as the one used to provide
Access Traffic Steering, Switching, and Splitting (ATSSS) must be Access Traffic Steering, Switching, and Splitting (ATSSS) must be
optimized to reduce latency [TS23501]. optimized to reduce latency [TS23501].
1.2. Network-Assisted Connections: The Rationale 1.2. Network-Assisted Connections: The Rationale
This document specifies an application proxy, called Transport This document specifies an application proxy called Transport
Converter. A Transport Converter is a function that is installed by Converter. A Transport Converter is a function that is installed by
a network operator to aid the deployment of TCP extensions and to a network operator to aid the deployment of TCP extensions and to
provide the benefits of such extensions to clients in particular. A provide the benefits of such extensions to Clients in particular. A
Transport Converter may provide conversion service for one or more Transport Converter may provide conversion service for one or more
TCP extensions. Which TCP extensions are eligible to the conversion TCP extensions. Which TCP extensions are eligible for the conversion
service is deployment-specific. The conversion service is provided service is deployment specific. The conversion service is provided
by means of the 0-RTT TCP Convert Protocol (Convert), that is an by means of the 0-RTT TCP Convert Protocol (Convert), which is an
application-layer protocol which uses a specific TCP port number on application-layer protocol that uses a specific TCP port number on
the Converter. the Converter.
The Convert Protocol provides Zero Round-Trip Time (0-RTT) conversion The Convert Protocol provides Zero Round-Trip Time (0-RTT) conversion
service since no extra delay is induced by the protocol compared to service since no extra delay is induced by the protocol compared to
connections that are not proxied. Particularly, the Convert Protocol connections that are not proxied. Particularly, the Convert Protocol
does not require extra signaling setup delays before making use of does not require extra signaling setup delays before making use of
the conversion service. The Convert Protocol does not require any the conversion service. The Convert Protocol does not require any
encapsulation (no tunnels, whatsoever). encapsulation (no tunnels, whatsoever).
The Transport Converter adheres to the main steps drawn in Section 3 The Transport Converter adheres to the main steps drawn in Section 3
of [RFC1919]. In particular, a Transport Converter achieves the of [RFC1919]. In particular, a Transport Converter achieves the
following: following:
o Listen for client sessions; * Listening for Client sessions;
o Receive from a client the address of the server; * Receiving the address of the Server from the Client;
o Setup a session to the server; * Setting up a session to the Server;
o Relay control messages and data between the client and the server; * Relaying control messages and data between the Client and the
Server;
o Perform access controls according to local policies. * Performing access controls according to local policies.
The main advantage of network-assisted conversion services is that The main advantage of network-assisted conversion services is that
they enable new TCP extensions to be used on a subset of the path they enable new TCP extensions to be used on a subset of the path
between endpoints, which encourages the deployment of these between endpoints, which encourages the deployment of these
extensions. Furthermore, the Transport Converter allows the client extensions. Furthermore, the Transport Converter allows the Client
and the server to directly negotiate TCP extensions for the sake of and the Server to directly negotiate TCP extensions for the sake of
native support along the full path. native support along the full path.
The Convert Protocol is a generic mechanism to provide 0-RTT The Convert Protocol is a generic mechanism to provide 0-RTT
conversion service. As a sample applicability use case, this conversion service. As a sample applicability use case, this
document specifies how the Convert Protocol applies for Multipath document specifies how the Convert Protocol applies for Multipath
TCP. It is out of scope of this document to provide a comprehensive TCP. It is out of scope of this document to provide a comprehensive
list of all potential conversion services. Applicability documents list of all potential conversion services. Applicability documents
may be defined in the future. may be defined in the future.
This document does not assume that all the traffic is eligible to the This document does not assume that all the traffic is eligible for
network-assisted conversion service. Only a subset of the traffic the network-assisted conversion service. Only a subset of the
will be forwarded to a Transport Converter according to a set of traffic will be forwarded to a Transport Converter according to a set
policies. These policies, and how they are communicated to of policies. These policies, and how they are communicated to
endpoints, are out of scope. Furthermore, it is possible to bypass endpoints, are out of scope. Furthermore, it is possible to bypass
the Transport Converter to connect directly to the servers that the Transport Converter to connect directly to the Servers that
already support the required TCP extension(s). already support the required TCP extension(s).
This document assumes an explicit model in which a client is This document assumes an explicit model in which a Client is
configured with one or a list of Transport Converters (statically or configured with one or a list of Transport Converters (statically or
through protocols such as [I-D.boucadair-tcpm-dhc-converter]). through protocols such as [DHC-CONVERTER]). Configuration means are
Configuration means are outside the scope of this document. outside the scope of this document.
The use of a Transport Converter means that there is no end-to-end The use of a Transport Converter means that there is no end-to-end
transport connection between the client and server. This could transport connection between the Client and Server. This could
potentially create problems in some scenarios such as those discussed potentially create problems in some scenarios such as those discussed
in Section 4 of [RFC3135]. Some of these problems may not be in Section 4 of [RFC3135]. Some of these problems may not be
applicable, for example, a Transport Converter can inform a client by applicable. For example, a Transport Converter can inform a Client
means of Network Failure (65) or Destination Unreachable (97) error by means of Network Failure (65) or Destination Unreachable (97)
messages (Section 6.2.8) that it encounters a failure problem; the error messages (Section 6.2.8) that it encounters a failure problem;
client can react accordingly. An endpoint, or its network the Client can react accordingly. An endpoint, or its network
administrator, can assess the benefit provided by the Transport administrator, can assess the benefit provided by the Transport
Converter service versus the risk. This is one reason why the Converter service versus the risk. This is one reason why the
Transport Converter functionality has to be explicitly requested by Transport Converter functionality has to be explicitly requested by
an endpoint. an endpoint.
This document is organized as follows. First, Section 2 provides a This document is organized as follows:
brief overview of the differences between the well-known SOCKS
protocol and the 0-RTT Convert protocol. Section 4 provides a brief Section 3 provides a brief overview of the differences between the
explanation of the operation of Transport Converters. Then, well-known SOCKS protocol and the 0-RTT TCP Convert Protocol.
Section 6 describes the Convert Protocol. Section 7 discusses how
Transport Converters can be used to support different TCP extensions. Section 4 provides a brief explanation of the operation of
Section 8 then discusses the interactions with middleboxes, while Transport Converters.
Section 9 focuses on the security considerations. Appendix A
describes how a TCP stack would need to support the protocol Section 5 includes a set of sample examples to illustrate the
described in this document. overall behavior.
Section 6 describes the Convert Protocol.
Section 7 discusses how Transport Converters can be used to
support different TCP extensions.
Section 8 then discusses the interactions with middleboxes.
Section 9 focuses on security considerations.
Appendix A describes how a TCP stack would need to support the
protocol described in this document.
1.3. Applicability Scope 1.3. Applicability Scope
0-RTT TCP Convert Protocol specified in this document MUST be used in The 0-RTT TCP Convert Protocol specified in this document MUST be
a single administrative domain deployment model. That is, the entity used in a single administrative domain deployment model. That is,
offering the connectivity service to a client is also be entity which the entity offering the connectivity service to a Client is also the
owns and operates the Transport Converter, with no transit over a entity that owns and operates the Transport Converter, with no
third-party network. transit over a third-party network.
Future deployment of Transport Converters by third parties MUST Future deployment of Transport Converters by third parties MUST
adhere to the mutual authentication requirements in Section 9.2 to adhere to the mutual authentication requirements in Section 9.2 to
prevent illegitimate traffic interception (Section 9.4), in prevent illegitimate traffic interception (Section 9.4) in
particular. particular.
2. Differences with SOCKSv5 2. Conventions and Definitions
Several IETF protocols provide proxy services; the closest to the The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
0-RTT Convert protocol being the SOCKSv5 protocol [RFC1928]. This "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
protocol is already used to deploy Multipath TCP in some cellular "OPTIONAL" in this document are to be interpreted as described in
networks (Section 2.2 of [RFC8041]). BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Differences with SOCKSv5
Several IETF protocols provide proxy services, the closest to the
0-RTT TCP Convert Protocol being the SOCKSv5 protocol [RFC1928].
This protocol is already used to deploy Multipath TCP in some
cellular networks (Section 2.2 of [RFC8041]).
A SOCKS Client creates a connection to a SOCKS Proxy, exchanges A SOCKS Client creates a connection to a SOCKS Proxy, exchanges
authentication information, and indicates the IP address and port authentication information, and indicates the IP address and port
number of the target Server. At this point, the SOCKS Proxy creates number of the target Server. At this point, the SOCKS Proxy creates
a connection towards the target Server and relays all data between a connection towards the target Server and relays all data between
the two proxied connections. The operation of an implementation the two proxied connections. The operation of an implementation
based on SOCKSv5 (without authentication) is illustrated in Figure 1. based on SOCKSv5 (without authentication) is illustrated in Figure 1.
Client SOCKS Proxy Server Client SOCKS Proxy Server
| | | | | |
skipping to change at page 7, line 42 skipping to change at line 348
| Data1 | | | Data1 | |
| | --------------------> | | | --------------------> |
| | Data1 | | | Data1 |
| | <-------------------- | | | <-------------------- |
| | Data2 | | | Data2 |
| <-------------------- | | | <-------------------- | |
| Data2 | | | Data2 | |
... ...
Figure 1: Establishment of a TCP Connection through a SOCKS Proxy Figure 1: Establishment of a TCP Connection through a SOCKS Proxy
Without Authentication without Authentication
When SOCKS is used, an "end-to-end" connection between a Client and a When SOCKS is used, an "end-to-end" connection between a Client and a
Server becomes a sequence of two TCP connections that are glued Server becomes a sequence of two TCP connections that are glued
together on the SOCKS Proxy. The SOCKS Client and Server exchange together on the SOCKS Proxy. The SOCKS Client and Server exchange
control information at the beginning of the bytestream on the Client- control information at the beginning of the bytestream on the Client-
Proxy connection. The SOCKS Proxy then creates the connection with Proxy connection. The SOCKS Proxy then creates the connection with
the target Server and then glues the two connections together so that the target Server and then glues the two connections together so that
all bytes sent by the application (Client) to the SOCKS Proxy are all bytes sent by the application (Client) to the SOCKS Proxy are
relayed to the Server and vice versa. relayed to the Server and vice versa.
The Convert Protocol is also used on TCP proxies that relay data The Convert Protocol is also used on TCP proxies that relay data
between an upstream and a downstream connection, but there are between an upstream and a downstream connection, but there are
important differences with SOCKSv5. A first difference is that the important differences with SOCKSv5. A first difference is that the
0-RTT Convert protocol exchanges all the control information during 0-RTT TCP Convert Protocol exchanges all the control information
the initial RTT. This reduces the connection establishment delay during the initial RTT. This reduces the connection establishment
compared to SOCKS which requires two or more round-trip-times before delay compared to SOCKS, which requires two or more round-trip times
the establishment of the downstream connection towards the final before the establishment of the downstream connection towards the
destination. In today's Internet, latency is an important metric and final destination. In today's Internet, latency is an important
various protocols have been tuned to reduce their latency metric, and various protocols have been tuned to reduce their latency
[I-D.arkko-arch-low-latency]. A recently proposed extension to SOCKS [LOW-LATENCY]. A recently proposed extension to SOCKS leverages the
leverages the TCP Fast Open (TFO) option TCP Fast Open (TFO) option [INTAREA-SOCKS] to reduce this delay.
[I-D.olteanu-intarea-socks-6] to reduce this delay.
A second difference is that the Convert Protocol explicitly takes the A second difference is that the Convert Protocol explicitly takes the
TCP extensions into account. By using the Convert Protocol, the TCP extensions into account. By using the Convert Protocol, the
Client can learn whether a given TCP extension is supported by the Client can learn whether a given TCP extension is supported by the
destination Server. This enables the Client to bypass the Transport destination Server. This enables the Client to bypass the Transport
Converter when the Server supports the required TCP extension(s). Converter when the Server supports the required TCP extension(s).
Neither SOCKSv5 [RFC1928] nor the proposed SOCKSv6 Neither SOCKSv5 [RFC1928] nor the proposed SOCKSv6 [INTAREA-SOCKS]
[I-D.olteanu-intarea-socks-6] provide such a feature. provide such a feature.
A third difference is that a Transport Converter will only confirm A third difference is that a Transport Converter will only confirm
the establishment of the connection initiated by the Client provided the establishment of the connection initiated by the Client provided
that the downstream connection has already been accepted by the that the downstream connection has already been accepted by the
Server. If the Server refuses the connection establishment attempt Server. If the Server refuses the connection establishment attempt
from the Transport Converter, then the upstream connection from the from the Transport Converter, then the upstream connection from the
Client is rejected as well. This feature is important for Client is rejected as well. This feature is important for
applications that check the availability of a Server or use the time applications that check the availability of a Server or use the time
to connect as a hint on the selection of a Server [RFC8305]. to connect as a hint on the selection of a Server [RFC8305].
A fourth difference is that the 0-RTT Convert protocol only allows A fourth difference is that the 0-RTT TCP Convert Protocol only
the Client to specify the IP address/port number of the destination allows the Client to specify the IP address/port number of the
server and not a DNS name. We evaluated an alternate design that destination Server and not a DNS name. We evaluated an alternate
included the DNS name of the remote peer instead of its IP address as design that included the DNS name of the remote peer instead of its
in SOCKS [RFC1928]. However, that design was not adopted because it IP address as in SOCKS [RFC1928]. However, that design was not
induces both an extra load and increased delays on the Transport adopted because it induces both an extra load and increased delays on
Converter to handle and manage DNS resolution requests. Note that the Transport Converter to handle and manage DNS resolution requests.
the name resolution at the Converter may fail (e.g., private names Note that the name resolution at the Converter may fail (e.g.,
discussed in Section 2.1 of [RFC6731]) or may not match the one that private names discussed in Section 2.1 of [RFC6731]) or may not match
would be returned by a Client's resolution library (e.g., Section 2.2 the one that would be returned by a Client's resolution library
of [RFC6731]). (e.g., Section 2.2 of [RFC6731]).
3. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
4. Architecture & Behaviors 4. Architecture and Behaviors
4.1. Functional Elements 4.1. Functional Elements
The Convert Protocol considers three functional elements: The Convert Protocol considers three functional elements:
o Clients; * Clients
o Transport Converters; * Transport Converters
o Servers. * Servers
A Transport Converter is a network function that proxies all data A Transport Converter is a network function that proxies all data
exchanged over one upstream connection to one downstream connection exchanged over one upstream connection to one downstream connection
and vice versa (Figure 2). The Transport Converter, thus, maintains and vice versa (Figure 2). Thus, the Transport Converter maintains
state that associates one upstream connection to a corresponding state that associates one upstream connection to a corresponding
downstream connection. downstream connection.
A connection can be initiated from both sides of the Transport A connection can be initiated from both sides of the Transport
Converter (External realm, Internal realm). Converter (External realm, Internal realm).
| |
: :
| |
+------------+ +------------+
skipping to change at page 9, line 50 skipping to change at line 443
Connections Connections
"Client" refers to a software instance embedded on a host that can "Client" refers to a software instance embedded on a host that can
reach a Transport Converter in the internal realm. The "Client" can reach a Transport Converter in the internal realm. The "Client" can
initiate connections via a Transport Converter (referred to as initiate connections via a Transport Converter (referred to as
outgoing connections). Also, the "Client" can accept incoming outgoing connections). Also, the "Client" can accept incoming
connections via a Transport Converter (referred to as incoming connections via a Transport Converter (referred to as incoming
connections). connections).
A Transport Converter can be embedded in a standalone device or be A Transport Converter can be embedded in a standalone device or be
activated as a service on a router. How such function is enabled is activated as a service on a router. How such a function is enabled
deployment-specific. is deployment specific.
The architecture assumes that new software will be installed on the The architecture assumes that new software will be installed on the
Client hosts to interact with one or more Transport Converters. Client hosts to interact with one or more Transport Converters.
Furthermore, the architecture allows for making use of new TCP Furthermore, the architecture allows for making use of new TCP
extensions even if those are not supported by a given server. extensions even if those are not supported by a given Server.
A Client is configured, through means that are outside the scope of A Client is configured, through means that are outside the scope of
this document, with the names and/or the addresses of one or more this document, with the names and/or addresses of one or more
Transport Converters and the TCP extensions that they support. The Transport Converters and the TCP extensions that they support. The
procedure for selecting a Transport Converter among a list of procedure for selecting a Transport Converter among a list of
configured Transport Converters is outside the scope of this configured Transport Converters is outside the scope of this
document. document.
One of the benefits of this design is that different transport One of the benefits of this design is that different transport
protocol extensions can be used on the upstream and the downstream protocol extensions can be used on the upstream and the downstream
connections. This encourages the deployment of new TCP extensions connections. This encourages the deployment of new TCP extensions
until they are widely supported by servers, in particular. until they are widely supported, in particular, by Servers.
The architecture does not mandate anything on the Server side. The architecture does not mandate anything on the Server side.
Similar to SOCKS, the architecture does not interfere with end-to-end Similar to SOCKS, the architecture does not interfere with end-to-end
TLS connections [RFC8446] between the Client and the Server TLS connections [RFC8446] between the Client and the Server
(Figure 3). In other words, end-to-end TLS is supported in the (Figure 3). In other words, end-to-end TLS is supported in the
presence of a Converter. presence of a Converter.
Client Transport Server Client Transport Server
| Converter | | Converter |
| | | | | |
/==========================================\ /==========================================\
| End-to-end TLS | | End-to-end TLS |
\==========================================/ \==========================================/
* TLS messages exchanged between the Client * TLS messages exchanged between the Client
and the Server are not shown. and the Server are not shown.
Figure 3: End-to-end TLS via a Transport Converter Figure 3: End-to-end TLS via a Transport Converter
It is out of scope of this document to elaborate on specific It is out of scope of this document to elaborate on specific
considerations related to the use of TLS in the Client-Converter considerations related to the use of TLS in the Client-Converter
connection leg to exchange Convert messages (in addition to the end- connection leg to exchange Convert messages (in addition to the end-
to-end TLS connection). In particular, (1) assessment whether 0-RTT to-end TLS connection). In particular, (1) assessment of whether
data mode discussed in Section 2.3 of [RFC8446] is safe under replay 0-RTT data mode discussed in Section 2.3 of [RFC8446] is safe under
and (2) specification of a profile for its use (Section E.5 of replay and (2) specification of a profile for its use (Appendix E.5
[RFC8446]) are out of scope. of [RFC8446]) are out of scope.
4.2. Theory of Operation 4.2. Theory of Operation
At a high level, the objective of the Transport Converter is to allow At a high level, the objective of the Transport Converter is to allow
the use a specific extension, e.g., Multipath TCP, on a subset of the the use a specific extension, e.g., Multipath TCP, on a subset of the
path even if the peer does not support this extension. This is path even if the peer does not support this extension. This is
illustrated in Figure 4 where the Client initiates a Multipath TCP illustrated in Figure 4 where the Client initiates a Multipath TCP
connection with the Transport Converter (packets belonging to the connection with the Transport Converter (packets belonging to the
Multipath TCP connection are shown with "===") while the Transport Multipath TCP connection are shown with "===") while the Transport
Converter uses a TCP connection with the Server. Converter uses a TCP connection with the Server.
skipping to change at page 11, line 25 skipping to change at line 510
Client Transport Server Client Transport Server
| Converter | | Converter |
| | | | | |
|==================>|--------------------->| |==================>|--------------------->|
| | | | | |
|<==================|<---------------------| |<==================|<---------------------|
| | | | | |
Multipath TCP packets TCP packets Multipath TCP packets TCP packets
Figure 4: An Example of 0-RTT Network-Assisted Outgoing MPTCP Figure 4: An Example of 0-RTT Network-Assisted Outgoing MPTCP
Connection Connection
The packets belonging to a connection established through a Transport The packets belonging to a connection established through a Transport
Converter may follow a different path than the packets directly Converter may follow a different path than the packets directly
exchanged between the Client and the Server. Deployments should exchanged between the Client and the Server. Deployments should
minimize the possible additional delay by carefully selecting the minimize the possible additional delay by carefully selecting the
location of the Transport Converter used to reach a given location of the Transport Converter used to reach a given
destination. destination.
When establishing a connection, the Client can, depending on local When establishing a connection, the Client can, depending on local
policies, either contact the Server directly (e.g., by sending a TCP policies, either contact the Server directly (e.g., by sending a TCP
SYN towards the Server) or create the connection via a Transport SYN towards the Server) or create the connection via a Transport
Converter. In the latter case (that is, the conversion service is Converter. In the latter case (that is, the conversion service is
used), the Client initiates a connection towards the Transport used), the Client initiates a connection towards the Transport
Converter and indicates the IP address and port number of the Server Converter and indicates the IP address and port number of the Server
within the connection establishment packet. Doing so enables the within the connection establishment packet. Doing so enables the
Transport Converter to immediately initiate a connection towards that Transport Converter to immediately initiate a connection towards that
Server, without experiencing an extra delay. The Transport Converter Server without experiencing an extra delay. The Transport Converter
waits until the receipt of the confirmation that the Server agrees to waits until the receipt of the confirmation that the Server agrees to
establish the connection before confirming it to the Client. establish the connection before confirming it to the Client.
The Client places the destination address and port number of the The Client places the destination address and port number of the
Server in the payload of the SYN sent to the Transport Converter to Server in the payload of the SYN sent to the Transport Converter to
minimize connection establishment delays. The Transport Converter minimize connection establishment delays. The Transport Converter
maintains two connections that are combined together: maintains two connections that are combined together:
o the upstream connection is the one between the Client and the * The upstream connection is the one between the Client and the
Transport Converter. Transport Converter.
o the downstream connection is the one between the Transport * The downstream connection is the one between the Transport
Converter and the Server. Converter and the Server.
Any user data received by the Transport Converter over the upstream Any user data received by the Transport Converter over the upstream
(or downstream) connection is proxied over the downstream (or (or downstream) connection is proxied over the downstream (or
upstream) connection. upstream) connection.
Figure 5 illustrates the establishment of an outgoing TCP connection Figure 5 illustrates the establishment of an outgoing TCP connection
by a Client through a Transport Converter. by a Client through a Transport Converter.
o Note: The information shown between brackets in Figure 5 (and | Note: The information shown between brackets in Figure 5 (and
other figures in the document) refers to Convert Protocol messages | other figures in the document) refers to Convert Protocol
described in Section 6. | messages described in Section 6.
Transport Transport
Client Converter Server Client Converter Server
| | | | | |
|SYN [->Server:port]| SYN | |SYN [->Server:port]| SYN |
|------------------>|--------------------->| |------------------>|--------------------->|
|<------------------|<---------------------| |<------------------|<---------------------|
| SYN+ACK [ ] | SYN+ACK | | SYN+ACK [ ] | SYN+ACK |
| ... | ... | | ... | ... |
Figure 5: Establishment of an Outgoing TCP Connection Through a Figure 5: Establishment of an Outgoing TCP Connection through a
Transport Converter Transport Converter
The Client sends a SYN destined to the Transport Converter. The The Client sends a SYN destined to the Transport Converter. The
payload of this SYN contains the address and port number of the payload of this SYN contains the address and port number of the
Server. The Transport Converter does not reply immediately to this Server. The Transport Converter does not reply immediately to this
SYN. It first tries to create a TCP connection towards the target SYN. It first tries to create a TCP connection towards the target
Server. If this upstream connection succeeds, the Transport Server. If this upstream connection succeeds, the Transport
Converter confirms the establishment of the connection to the Client Converter confirms the establishment of the connection to the Client
by returning a SYN+ACK and the first bytes of the bytestream contain by returning a SYN+ACK and the first bytes of the bytestream contain
information about the TCP options that were negotiated with the information about the TCP options that were negotiated with the
Server. Also, a state entry is instantiated for this connection. Server. Also, a state entry is instantiated for this connection.
This state entry is used by the Converter to handle subsequent This state entry is used by the Converter to handle subsequent
messages belonging to the connection. messages belonging to the connection.
The connection can also be established from the Internet towards a The connection can also be established from the Internet towards a
Client via a Transport Converter (Figure 6). This is typically the Client via a Transport Converter (Figure 6). This is typically the
case when the Client hosts an application server that listens to a case when the Client hosts an application Server that listens to a
specific port number. When the Converter receives an incoming SYN specific port number. When the Converter receives an incoming SYN
from a remote host, it checks if it can provide the conversion from a remote host, it checks if it can provide the conversion
service for the destination IP address and destination port number of service for the destination IP address and destination port number of
that SYN. The Transport Converter receives this SYN because it is, that SYN. The Transport Converter receives this SYN because it is,
for example, on the path between the remote host and the Client or it for example, on the path between the remote host and the Client or it
provides address sharing service for the Client (Section 2 of provides address-sharing service for the Client (Section 2 of
[RFC6269]). If the check fails, the packet is silently ignored by [RFC6269]). If the check fails, the packet is silently ignored by
the Converter. If the check is successful, the Converter tries to the Converter. If the check is successful, the Converter tries to
initiate a TCP connection towards the Client from its own address and initiate a TCP connection towards the Client from its own address and
using its configured TCP options. In the SYN that corresponds to using its configured TCP options. In the SYN that corresponds to
this connection attempt, the Transport Convert inserts a TLV message this connection attempt, the Transport Convert inserts a TLV message
that indicates the source address and port number of the remote host. that indicates the source address and port number of the remote host.
A transport session entry is created by the Converter for this A transport session entry is created by the Converter for this
connection. SYN+ACK and ACK will be then exchanged between the connection. SYN+ACK and ACK will then be exchanged between the
Client, the Converter, and remote host to confirm the establishment Client, the Converter, and remote host to confirm the establishment
of the connection. The Converter uses the transport session entry to of the connection. The Converter uses the transport session entry to
proxy packets belonging to the connection. proxy packets belonging to the connection.
Transport Remote Transport Remote
Client Converter Host (RH) Client Converter Host (RH)
| | | | | |
|SYN [<-RH IP@:port]| SYN | |SYN [<-RH IP@:port]| SYN |
|<------------------|<---------------------| |<------------------|<---------------------|
|------------------>|--------------------->| |------------------>|--------------------->|
| SYN+ACK [ ] | SYN+ACK | | SYN+ACK [ ] | SYN+ACK |
| ... | ... | | ... | ... |
Figure 6: Establishment of an Incoming TCP Connection Through a Figure 6: Establishment of an Incoming TCP Connection through a
Transport Converter Transport Converter
Standard TCP ([RFC0793], Section 3.4) allows a SYN packet to carry Standard TCP (Section 3.4 of [RFC0793]) allows a SYN packet to carry
data inside its payload but forbids the receiver from delivering it data inside its payload but forbids the receiver from delivering it
to the application until completion of the three-way-handshake. To to the application until completion of the three-way-handshake. To
enable applications to exchange data in a TCP handshake, this enable applications to exchange data in a TCP handshake, this
specification follows an approach similar to TCP Fast Open [RFC7413] specification follows an approach similar to TCP Fast Open [RFC7413]
and thus removes the constraint by allowing data in SYN packets to be and thus, removes the constraint by allowing data in SYN packets to
delivered to the Transport Converter application. be delivered to the Transport Converter application.
As discussed in [RFC7413], such change to TCP semantic raises two As discussed in [RFC7413], such change to TCP semantics raises two
issues. First, duplicate SYNs can cause problems for applications issues. First, duplicate SYNs can cause problems for applications
that rely on TCP; whether or not a given application is affected that rely on TCP; whether or not a given application is affected
dependes on the details of that application protocol. Second, TCP depends on the details of that application protocol. Second, TCP
suffers from SYN flooding attacks [RFC4987]. TFO solves these two suffers from SYN flooding attacks [RFC4987]. TFO solves these two
problems for applications that can tolerate replays by using the TCP problems for applications that can tolerate replays by using the TCP
Fast Open option that includes a cookie. However, the utilization of Fast Open option that includes a cookie. However, the utilization of
this option consumes space in the limited TCP header. Furthermore, this option consumes space in the limited TCP header. Furthermore,
there are situations, as noted in Section 7.3 of [RFC7413] where it there are situations, as noted in Section 7.3 of [RFC7413], where it
is possible to accept the payload of SYN packets without creating is possible to accept the payload of SYN packets without creating
additional security risks such as a network where addresses cannot be additional security risks such as a network where addresses cannot be
spoofed and the Transport Converter only serves a set of hosts that spoofed and the Transport Converter only serves a set of hosts that
are identified by these addresses. are identified by these addresses.
For these reasons, this specification does not mandate the use of the For these reasons, this specification does not mandate the use of the
TCP Fast Open option when the Client sends a connection establishment TCP Fast Open option when the Client sends a connection establishment
packet towards a Transport Converter. The Convert Protocol includes packet towards a Transport Converter. The Convert Protocol includes
an optional Cookie TLV that provides similar protection as the TCP an optional Cookie TLV that provides similar protection as the TCP
Fast Open option without consuming space in the TCP header. Fast Open option without consuming space in the TCP header.
Furthermore, this design allows for the use of longer cookies than Furthermore, this design allows for the use of longer cookies than
[RFC7413]. [RFC7413].
If the downstream (or upstream) connection fails for some reason If the downstream (or upstream) connection fails for some reason
(excessive retransmissions, reception of an RST segment, etc.), then (excessive retransmissions, reception of an RST segment, etc.), then
the Converter reacts by forcing the tear-down of the upstream (or the Converter reacts by forcing the teardown of the upstream (or
downstream) connection. In particular, if an ICMP error message that downstream) connection. In particular, if an ICMP error message that
indicates a hard error is received on the downstream connection, the indicates a hard error is received on the downstream connection, the
Converter echoes the Code field of that ICMP message in a Destination Converter echoes the Code field of that ICMP message in a Destination
Unreachable Error TLV (see Section 6.2.8) that it transmits to the Unreachable Error TLV (see Section 6.2.8) that it transmits to the
Client. Note that if an ICMP error message that indicates a soft Client. Note that if an ICMP error message that indicates a soft
error is received on the downstream connection, the Converter will error is received on the downstream connection, the Converter will
retransmit the corresponding data until it is acknowledged or the retransmit the corresponding data until it is acknowledged or the
connection times out. A classification of ICMP soft and hard errors connection times out. A classification of ICMP soft and hard errors
is provided in Table 1 of [RFC5461]. is provided in Table 1 of [RFC5461].
skipping to change at page 14, line 37 skipping to change at line 667
the Converter should initiate a graceful termination of the upstream the Converter should initiate a graceful termination of the upstream
connection. connection.
4.3. Data Processing at the Transport Converter 4.3. Data Processing at the Transport Converter
As mentioned in Section 4.2, the Transport Converter acts as a TCP As mentioned in Section 4.2, the Transport Converter acts as a TCP
proxy between the upstream connection (i.e., between the Client and proxy between the upstream connection (i.e., between the Client and
the Transport Converter) and the downstream connection (i.e., between the Transport Converter) and the downstream connection (i.e., between
the Transport Converter and the Server). the Transport Converter and the Server).
The control messages, discussed in Section 6, establish state The control messages (i.e., the Convert messages discussed in
(called, transport session entry) in the Transport Converter that Section 6) establish state (called transport session entry) in the
will enable it to proxy between the two TCP connections. Transport Converter that will enable it to proxy between the two TCP
connections.
The Transport Converter uses the transport session entry to proxy The Transport Converter uses the transport session entry to proxy
packets belonging to the connection. An implementation example of a packets belonging to the connection. An implementation example of a
transport session entry for TCP connections is shown in Figure 7. transport session entry for TCP connections is shown in Figure 7.
(C,c) <--> (T,t), (S,s), Lifetime (C,c) <--> (T,t), (S,s), Lifetime
Where:
* C and c are the source IP address and source port number
used by the Client for the upstream connection.
* S and s are the Server's IP address and port number.
* T and t are the source IP address and source port number
used by the Transport Converter to proxy the connection.
* Lifetime is a timer that tracks the remaining lifetime of
the entry as assigned by the Converter. When the timer
expires, the entry is deleted.
Figure 7: An Example of Transport Session Entry Figure 7: An Example of Transport Session Entry
Clients send packets bound to connections eligible to the conversion Where:
* C and c are the source IP address and source port number used by
the Client for the upstream connection.
* S and s are the Server's IP address and port number.
* T and t are the source IP address and source port number used by
the Transport Converter to proxy the connection.
* Lifetime is a timer that tracks the remaining lifetime of the
entry as assigned by the Converter. When the timer expires, the
entry is deleted.
Clients send packets bound to connections eligible for the conversion
service to the provisioned Transport Converter and destination port service to the provisioned Transport Converter and destination port
number. This applies for both control messages and data. Additional number. This applies for both control messages and data. Additional
information is supplied by Clients to the Transport Converter by information is supplied by Clients to the Transport Converter by
means of Convert messages as detailed in Section 6. User data can be means of Convert messages as detailed in Section 6. User data can be
included in SYN or non-SYN messages. User data is unambiguously included in SYN or non-SYN messages. User data is unambiguously
distinguished from Convert TLVs by a Transport Converter owing to the distinguished from Convert TLVs by a Transport Converter owing to the
Convert Fixed Header in the Convert messages (Section 6.1). These Convert Fixed Header in the Convert messages (Section 6.1). These
Convert TLVs are destined to the Transport Convert and are, thus, Convert TLVs are destined to the Transport Convert and are, thus,
removed by the Transport Converter when proxying between the two removed by the Transport Converter when proxying between the two
connections. connections.
Upon receipt of a packet that belongs to an existing connection Upon receipt of a packet that belongs to an existing connection
between a Client and the Transport Converter the Converter proxies between a Client and the Transport Converter, the Converter proxies
the user data to the Server using the information stored in the the user data to the Server using the information stored in the
corresponding transport session entry. For example, in reference to corresponding transport session entry. For example, in reference to
Figure 7, the Transport Converter proxies the data received from (C, Figure 7, the Transport Converter proxies the data received from
c) downstream using (T,t) as source transport address and (S,s) as (C,c) downstream using (T,t) as source transport address and (S,s) as
destination transport address. destination transport address.
A similar process happens for data sent from the Server. The A similar process happens for data sent from the Server. The
Converter acts as a TCP proxy and sends the data to the Client Converter acts as a TCP proxy and sends the data to the Client
relying upon the information stored in a transport session entry. relying upon the information stored in a transport session entry.
The Converter associates a lifetime with state entries used to bind The Converter associates a lifetime with state entries used to bind
an upstream connection with its downstream connection. an upstream connection with its downstream connection.
When Multipath TCP is used between the Client and the Transport When Multipath TCP is used between the Client and the Transport
Converter, the Converter maintains more state (e.g. information about Converter, the Converter maintains more state (e.g., information
the subflows) for each Multipath TCP connection. The procedure about the subflows) for each Multipath TCP connection. The procedure
described above continues to apply except that the Converter needs to described above continues to apply except that the Converter needs to
manage the establishment/termination of subflows and schedule packets manage the establishment/termination of subflows and schedule packets
among the established ones. These operations are part of the among the established ones. These operations are part of the
Multipath TCP implementation. They are independent of the Convert Multipath TCP implementation. They are independent of the Convert
protocol that only processes the Convert messages in the beginning of Protocol that only processes the Convert messages in the beginning of
the bytestream. the bytestream.
A Transport Converter may operate in address preservation mode (that A Transport Converter may operate in address preservation mode (that
is, the Converter does not rewrite the source IP address (i.e., is, the Converter does not rewrite the source IP address (i.e.,
C==T)) or address sharing mode (that is, an address pool is shared C==T)) or address-sharing mode (that is, an address pool is shared
among all Clients serviced by the Converter (i.e., C!=T)); refer to among all Clients serviced by the Converter (i.e., C!=T)); refer to
Section 4.4 for more details. Which behavior to use by a Transport Section 4.4 for more details. Which behavior to use by a Transport
Converter is deployment-specific. If address sharing mode is Converter is deployment specific. If address-sharing mode is
enabled, the Transport Converter MUST adhere to REQ-2 of [RFC6888] enabled, the Transport Converter MUST adhere to REQ-2 of [RFC6888],
which implies a default "IP address pooling" behavior of "Paired" (as which implies a default "IP address pooling" behavior of "Paired" (as
defined in Section 4.1 of [RFC4787]) MUST be supported. This defined in Section 4.1 of [RFC4787]) MUST be supported. This
behavior is meant to avoid breaking applications that depend on the behavior is meant to avoid breaking applications that depend on the
source address remaining constant. source address remaining constant.
4.4. Address Preservation vs. Address Sharing 4.4. Address Preservation vs. Address Sharing
The Transport Converter is provided with instructions about the The Transport Converter is provided with instructions about the
behavior to adopt with regards to the processing of source addresses behavior to adopt with regard to the processing of source addresses
of outgoing packets. The following sub-sections discusses two of outgoing packets. The following subsections discuss two
deployment models for illustration purposes. It is out of the scope deployment models for illustration purposes. It is out of the scope
of this document to make a recommendation. of this document to make a recommendation.
4.4.1. Address Preservation 4.4.1. Address Preservation
In this model, the visible source IP address of a packet proxied by a In this model, the visible source IP address of a packet proxied by a
Transport Converter to a Server is an IP address of the end host Transport Converter to a Server is an IP address of the end host
(Client). No dedicated IP address pool is provisioned to the (Client). No dedicated IP address pool is provisioned to the
Transport Converter, but the Transport Converter is located on the Transport Converter, but the Transport Converter is located on the
path between the Client and the Server. path between the Client and the Server.
For Multipath TCP, the Transport Converter preserves the source IP For Multipath TCP, the Transport Converter preserves the source IP
address used by the Client when establishing the initial subflow. address used by the Client when establishing the initial subflow.
Data conveyed in secondary subflows will be proxied by the Transport Data conveyed in secondary subflows will be proxied by the Transport
Converter using the source IP address of the initial subflow. An Converter using the source IP address of the initial subflow. An
example of a proxied Multipath TCP connection with address example of a proxied Multipath TCP connection with address
preservation is shown in Figure 8. preservation is shown in Figure 8.
Transport Transport
Client Converter Server Client Converter Server
@:C1,C2 @:Tc @:S @:C1,C2 @:Tc @:S
|| | | || | |
|src:C1 SYN dst:Tc|src:C1 dst:S| |src:C1 SYN dst:Tc|src:C1 dst:S|
|-------MPC [->S:port]------->|-------SYN------->| |-------MPC [->S:port]------->|-------SYN------->|
|| | | || | |
||dst:C1 src:Tc|dst:C1 src:S| ||dst:C1 src:Tc|dst:C1 src:S|
|<---------SYN/ACK------------|<-----SYN/ACK-----| |<---------SYN/ACK------------|<-----SYN/ACK-----|
|| | | || | |
|src:C1 dst:Tc|src:C1 dst:S| |src:C1 dst:Tc|src:C1 dst:S|
|------------ACK------------->|-------ACK------->| |------------ACK------------->|-------ACK------->|
| | | | | |
|src:C2 ... dst:Tc| ... | |src:C2 ... dst:Tc| ... |
||<-----Secondary Subflow---->|src:C1 dst:S| ||<-----Secondary Subflow---->|src:C1 dst:S|
|| |-------data------>| || |-------data------>|
| .. | ... | | .. | ... |
Legend: Legend:
Tc: IP address used by the Transport Converter on the internal Tc: IP address used by the Transport Converter on the internal
realm. realm.
Figure 8: Example of Address Preservation Figure 8: Example of Address Preservation
The Transport Converter must be on the forwarding path of incoming The Transport Converter must be on the forwarding path of incoming
traffic. Because the same (destination) IP address is used for both traffic. Because the same (destination) IP address is used for both
proxied and non-proxied connections, the Transport Converter should proxied and non-proxied connections, the Transport Converter should
not drop incoming packets it intercepts if no matching entry is found not drop incoming packets it intercepts if no matching entry is found
for the packets. Unless explicitly configured otherwise, such for the packets. Unless explicitly configured otherwise, such
packets are forwarded according to the instructions of a local packets are forwarded according to the instructions of a local
forwarding table. forwarding table.
4.4.2. Address/Prefix Sharing 4.4.2. Address/Prefix Sharing
A pool of global IPv4 addresses is provisioned to the Transport A pool of global IPv4 addresses is provisioned to the Transport
Converter along with possible instructions about the address sharing Converter along with possible instructions about the address-sharing
ratio to apply (see Appendix B of [RFC6269]). An address is thus ratio to apply (see Appendix B of [RFC6269]). An address is thus
shared among multiple clients. shared among multiple Clients.
Likewise, rewriting the source IPv6 prefix [RFC6296] may be used to Likewise, rewriting the source IPv6 prefix [RFC6296] may be used to
ease redirection of incoming IPv6 traffic towards the appropriate ease redirection of incoming IPv6 traffic towards the appropriate
Transport Converter. A pool of IPv6 prefixes is then provisioned to Transport Converter. A pool of IPv6 prefixes is then provisioned to
the Transport Converter for this purpose. the Transport Converter for this purpose.
Adequate forwarding policies are enforced so that traffic destined to Adequate forwarding policies are enforced so that traffic destined to
an address of such pool is intercepted by the appropriate Transport an address of such a pool is intercepted by the appropriate Transport
Converter. Unlike Section 4.4.1, the Transport Converter drops Converter. Unlike Section 4.4.1, the Transport Converter drops
incoming packets which do not match an active transport session incoming packets that do not match an active transport session entry.
entry.
An example is shown in Figure 9. An example is shown in Figure 9.
Transport Transport
Client Converter Server Client Converter Server
@:C @:Tc|Te @:S @:C @:Tc|Te @:S
| | | | | |
|src:C dst:Tc|src:Te dst:S| |src:C dst:Tc|src:Te dst:S|
|-------SYN [->S:port]------->|-------SYN------->| |-------SYN [->S:port]------->|-------SYN------->|
| | | | | |
|dst:C src:Tc|dst:Te src:S| |dst:C src:Tc|dst:Te src:S|
|<---------SYN/ACK------------|<-----SYN/ACK-----| |<---------SYN/ACK------------|<-----SYN/ACK-----|
| | | | | |
|src:C dst:Tc|src:Te dst:S| |src:C dst:Tc|src:Te dst:S|
|------------ACK------------->|-------ACK------->| |------------ACK------------->|-------ACK------->|
| | | | | |
| ... | ... | | ... | ... |
Legend: Legend:
Tc: IP address used by the Transport Converter on the internal Tc: IP address used by the Transport Converter on the internal
realm. realm.
Te: IP address used by the Transport Converter on the external Te: IP address used by the Transport Converter on the external
realm. realm.
Figure 9: Address Sharing Figure 9: Address Sharing
5. Sample Examples 5. Sample Examples
5.1. Outgoing Converter-Assisted Multipath TCP Connections 5.1. Outgoing Converter-Assisted Multipath TCP Connections
As an example, let us consider how the Convert Protocol can help the As an example, let us consider how the Convert Protocol can help the
deployment of Multipath TCP. We assume that both the Client and the deployment of Multipath TCP. We assume that both the Client and the
Transport Converter support Multipath TCP, but consider two different Transport Converter support Multipath TCP but consider two different
cases depending on whether the Server supports Multipath TCP or not. cases depending on whether or not the Server supports Multipath TCP.
As a reminder, a Multipath TCP connection is created by placing the As a reminder, a Multipath TCP connection is created by placing the
MP_CAPABLE (MPC) option in the SYN sent by the Client. MP_CAPABLE (MPC) option in the SYN sent by the Client.
Figure 10 describes the operation of the Transport Converter if the Figure 10 describes the operation of the Transport Converter if the
Server does not support Multipath TCP. Server does not support Multipath TCP.
Transport Transport
Client Converter Server Client Converter Server
|SYN, MPC | | |SYN, MPC | |
|[->Server:port] | SYN, MPC | |[->Server:port] | SYN, MPC |
|------------------>|--------------------->| |------------------>|--------------------->|
|<------------------|<---------------------| |<------------------|<---------------------|
| SYN+ACK,MPC [.] | SYN+ACK | | SYN+ACK,MPC [.] | SYN+ACK |
|------------------>|--------------------->| |------------------>|--------------------->|
| ACK, MPC | ACK | | ACK, MPC | ACK |
| ... | ... | | ... | ... |
Figure 10: Establishment of a Multipath TCP Connection through a Figure 10: Establishment of a Multipath TCP Connection through a
Transport Converter towards a Server that does not support Multipath Transport Converter towards a Server That Does Not support
TCP Multipath TCP
The Client tries to initiate a Multipath TCP connection by sending a The Client tries to initiate a Multipath TCP connection by sending a
SYN with the MP_CAPABLE option (MPC in Figure 10). The SYN includes SYN with the MP_CAPABLE option (MPC in Figure 10). The SYN includes
the address and port number of the target Server, that are extracted the address and port number of the target Server, that are extracted
and used by the Transport Converter to initiate a Multipath TCP and used by the Transport Converter to initiate a Multipath TCP
connection towards this Server. Since the Server does not support connection towards this Server. Since the Server does not support
Multipath TCP, it replies with a SYN+ACK that does not contain the Multipath TCP, it replies with a SYN+ACK that does not contain the
MP_CAPABLE option. The Transport Converter notes that the connection MP_CAPABLE option. The Transport Converter notes that the connection
with the Server does not support Multipath TCP and returns the with the Server does not support Multipath TCP and returns the
extended TCP header received from the Server to the Client. extended TCP header received from the Server to the Client.
Note that, if the TCP connection is reset for some reason, the Note that, if the TCP connection is reset for some reason, the
Converter tears down the Multipath TCP connection by transmitting a Converter tears down the Multipath TCP connection by transmitting an
MP_FASTCLOSE. Likewise, if the Multipath TCP connection ends with MP_FASTCLOSE. Likewise, if the Multipath TCP connection ends with
the transmission of DATA_FINs, the Converter terminates the TCP the transmission of DATA_FINs, the Converter terminates the TCP
connection by using FIN segments. As a side note, given that with connection by using FIN segments. As a side note, given that with
Multipath TCP, RST only has the scope of the subflow and will only Multipath TCP, RST only has the scope of the subflow and will only
close the concerned subflow but not affect the remaining subflows, close the concerned subflow but not affect the remaining subflows,
the Converter does not terminate the downstream TCP connection upon the Converter does not terminate the downstream TCP connection upon
receipt of an RST over a Multipath subflow. receipt of an RST over a Multipath subflow.
Figure 11 considers a Server that supports Multipath TCP. In this Figure 11 considers a Server that supports Multipath TCP. In this
case, it replies to the SYN sent by the Transport Converter with the case, it replies to the SYN sent by the Transport Converter with the
skipping to change at page 20, line 17 skipping to change at line 913
|SYN, MPC | | |SYN, MPC | |
|[->Server:port] | SYN, MPC | |[->Server:port] | SYN, MPC |
|------------------>|--------------------->| |------------------>|--------------------->|
|<------------------|<---------------------| |<------------------|<---------------------|
|SYN+ACK, MPC | SYN+ACK, MPC | |SYN+ACK, MPC | SYN+ACK, MPC |
|[MPC supported] | | |[MPC supported] | |
|------------------>|--------------------->| |------------------>|--------------------->|
| ACK, MPC | ACK, MPC | | ACK, MPC | ACK, MPC |
| ... | ... | | ... | ... |
Figure 11: Establishment of a Multipath TCP Connection through a Figure 11: Establishment of a Multipath TCP Connection through a
Converter towards an MPTCP-capable Server Converter towards an MPTCP-Capable Server
5.2. Incoming Converter-Assisted Multipath TCP Connection 5.2. Incoming Converter-Assisted Multipath TCP Connection
An example of an incoming Converter-assisted Multipath TCP connection An example of an incoming Converter-assisted Multipath TCP connection
is depicted in Figure 12. In order to support incoming connections is depicted in Figure 12. In order to support incoming connections
from remote hosts, the Client may use PCP [RFC6887] to instruct the from remote hosts, the Client may use the Port Control Protocol (PCP)
Transport Converter to create dynamic mappings. Those mappings will [RFC6887] to instruct the Transport Converter to create dynamic
be used by the Transport Converter to intercept an incoming TCP mappings. Those mappings will be used by the Transport Converter to
connection destined to the Client and convert it into a Multipath TCP intercept an incoming TCP connection destined to the Client and
connection. convert it into a Multipath TCP connection.
Typically, the Client sends a PCP request to the Converter asking to Typically, the Client sends a PCP request to the Converter asking to
create an explicit TCP mapping for (internal IP address, internal create an explicit TCP mapping for the internal IP address and
port number). The Converter accepts the request by creating a TCP internal port number. The Converter accepts the request by creating
mapping (internal IP address, internal port number, external IP a TCP mapping for the internal IP address, internal port number,
address, external port number). The external IP address, external external IP address, and external port number. The external IP
port number, and assigned lifetime are returned back the Client in address, external port number, and assigned lifetime are returned
the PCP response. The external IP address and external port number back to the Client in the PCP response. The external IP address and
will be then advertised by the Client (or the user) using an out-of- external port number will then be advertised by the Client (or the
band mechanism so that remote hosts can initiate TCP connections to user) using an out-of-band mechanism so that remote hosts can
the Client via the Converter. Note that the external and internal initiate TCP connections to the Client via the Converter. Note that
information may be the same. the external and internal information may be the same.
Then, when the Converter receives an incoming SYN, it checks its Then, when the Converter receives an incoming SYN, it checks its
mapping table to verify if there is an active mapping matching the mapping table to verify if there is an active mapping matching the
destination IP address and destination port of that SYN. If no entry destination IP address and destination port of that SYN. If no entry
is found, the Converter silently ignores the message. If an entry is is found, the Converter silently ignores the message. If an entry is
found, the Converter inserts an MP_CAPABLE option and Connect TLV in found, the Converter inserts an MP_CAPABLE option and Connect TLV in
the SYN packet, rewrites the source IP address to one of its IP the SYN packet, and rewrites the source IP address to one of its IP
addresses and, eventually, the destination IP address and port number addresses and, eventually, the destination IP address and port number
in accordance with the information stored in the mapping. SYN+ACK in accordance with the information stored in the mapping. SYN+ACK
and ACK will be then exchanged between the Client and the Converter and ACK will then be exchanged between the Client and the Converter
to confirm the establishment of the initial subflow. The Client can to confirm the establishment of the initial subflow. The Client can
add new subflows following normal Multipath TCP procedures. add new subflows following normal Multipath TCP procedures.
Transport Remote Transport Remote
Client Converter Host Client Converter Host
| | | | | |
|<--------------------|<-------------------| |<--------------------|<-------------------|
|SYN, MPC | SYN | |SYN, MPC | SYN |
|[Remote Host:port] | | |[Remote Host:port] | |
|-------------------->|------------------->| |-------------------->|------------------->|
| SYN+ACK, MPC | SYN+ACK | | SYN+ACK, MPC | SYN+ACK |
|<--------------------|<-------------------| |<--------------------|<-------------------|
| ACK, MPC | ACK | | ACK, MPC | ACK |
| ... | ... | | ... | ... |
Figure 12: Establishment of an Incoming Multipath TCP Connection Figure 12: Establishment of an Incoming Multipath TCP Connection
through a Transport Converter through a Transport Converter
It is out of scope of this document to define specific Convert TLVs It is out of scope of this document to define specific Convert TLVs
to manage incoming connections (that is, TLVs that mimic PCP to manage incoming connections (that is, TLVs that mimic PCP
messages). These TLVs can be defined in a separate document. messages). These TLVs can be defined in a separate document.
6. The Convert Protocol (Convert) 6. The Convert Protocol (Convert)
This section defines the Convert Protocol (Convert, for short) This section defines the Convert Protocol (Convert, for short)
messages that are exchanged between a Client and a Transport messages that are exchanged between a Client and a Transport
Converter. Converter.
The Transport Converter listens on a specific TCP port number for The Transport Converter listens on a specific TCP port number for
Convert messages from Clients. That port number is configured by an Convert messages from Clients. That port number is configured by an
administrator. Absent any policy, the Transport Converter SHOULD administrator. Absent any policy, the Transport Converter SHOULD
silently ignore SYNs with no Convert TLVs. silently ignore SYNs with no Convert TLVs.
Convert messages may appear only in SYN, SYN+ACK, or ACK. Convert messages may appear only in SYN, SYN+ACK, or ACK.
Convert messages MUST be included as the first bytes of the Convert messages MUST be included as the first bytes of the
bytestream. All Convert messages starts with a 32 bits long fixed bytestream. All Convert messages start with a fixed header that is
header (Section 6.1) followed by one or more Convert TLVs (Type, 32 bits long (Section 6.1) followed by one or more Convert TLVs
Length, Value) (Section 6.2). (Type, Length, Value) (Section 6.2).
If the initial SYN message contains user data in its payload (e.g., If the initial SYN message contains user data in its payload (e.g.,
[RFC7413]), that data MUST be placed right after the Convert TLVs see [RFC7413]), that data MUST be placed right after the Convert TLVs
when generating the SYN. when generating the SYN.
The protocol can be extended by defining new TLVs or bumping the The protocol can be extended by defining new TLVs or bumping the
version number if a different message format is needed. If a future version number if a different message format is needed. If a future
version is defined but with a different message format, the version version is defined but with a different message format, the version
negotiation procedure defined in Section 6.2.8 (see "Unsupported negotiation procedure defined in Section 6.2.8 (see "Unsupported
Version") is meant to agree on a version that is supported by both Version") is meant to agree on a version that is supported by both
peers. peers.
o Implementation note 1: Several implementers expressed concerns | Implementation note 1: Several implementers expressed concerns
about the use of TFO. As a reminder, the TFO Cookie protects from | about the use of TFO. As a reminder, the Fast Open Cookie
some attack scenarios that affect open servers like web servers. | protects from some attack scenarios that affect open servers
The Convert Protocol is different and, as discussed in RFC7413, | like web servers. The Convert Protocol is different and, as
there are different ways to protect from such attacks. Instead of | discussed in [RFC7413], there are different ways to protect
using a TFO cookie inside the TCP options, which consumes precious | from such attacks. Instead of using a Fast Open Cookie inside
space in the extended TCP header, the Convert Protocol supports | the TCP options, which consumes precious space in the extended
the utilization of a Cookie that is placed in the SYN payload. | TCP header, the Convert Protocol supports the utilization of a
This provides the same level of protection as a TFO Cookie in | Cookie that is placed in the SYN payload. This provides the
environments were such protection is required. | same level of protection as a Fast Open Cookie in environments
| were such protection is required.
o Implementation note 2: Error messages are not included in RST but |
sent in the bytestream. Implementers have indicated that | Implementation note 2: Error messages are not included in RST
processing RST on clients was difficult on some platforms. This | but sent in the bytestream. Implementers have indicated that
design simplifies client implementations. | processing RST on Clients was difficult on some platforms.
| This design simplifies Client implementations.
6.1. The Convert Fixed Header 6.1. The Convert Fixed Header
The Convert Protocol uses a 32 bits long fixed header that is sent by The Convert Protocol uses a fixed header that is 32 bits long sent by
both the Client and the Transport Converter over each established both the Client and the Transport Converter over each established
connection. This header indicates both the version of the protocol connection. This header indicates both the version of the protocol
used and the length of the Convert message. used and the length of the Convert message.
The Client and the Transport Converter MUST send the fixed-sized The Client and the Transport Converter MUST send the fixed-sized
header, shown in Figure 13, as the first four bytes of the header, shown in Figure 13, as the first four bytes of the
bytestream. bytestream.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Version | Total Length | Magic Number | | Version | Total Length | Magic Number |
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
Figure 13: The Convert Fixed Header Figure 13: The Convert Fixed Header
The Version is encoded as an 8 bits unsigned integer value. This The version is encoded as an 8-bit unsigned integer value. This
document specifies version 1. Version 0 is reserved by this document document specifies version 1. Version 0 is reserved by this document
and MUST NOT be used. and MUST NOT be used.
Note: Early versions of this specification don't use a dedicated | Note: Early versions of this specification don't use a
port number but only rely upon the IP address of the Converter. | dedicated port number but only rely upon the IP address of the
Having a bit set in the version field together with the length | Converter. Having a bit set in the Version field together with
field allows to avoid mis-interpreting a data in a SYN as Convert | the Total Length field avoids misinterpreting data in a SYN as
TLVs. Since the design was updated to use a specific service | Convert TLVs. Since the design was updated to use a specific
port, that constraint was relaxed. Version 0 would work but given | service port, that constraint was relaxed. Version 0 would
existing implementations already use Version 1, the use of Version | work, but given existing implementations already use Version 1,
0 is maintained as reserved. | the use of Version 0 is maintained as reserved.
The Total Length is the number of 32 bits word, including the header, The Total Length is the number of 32-bit words, including the header,
of the bytestream that are consumed by the Convert messages. Since of the bytestream that are consumed by the Convert messages. Since
Total Length is also an 8 bits unsigned integer, those messages Total Length is also an 8-bit unsigned integer, those messages cannot
cannot consume more than 1020 bytes of data. This limits the number consume more than 1020 bytes of data. This limits the number of
of bytes that a Transport Converter needs to process. A Total Length bytes that a Transport Converter needs to process. A Total Length of
of zero is invalid and the connection MUST be reset upon reception of zero is invalid and the connection MUST be reset upon reception of a
a header with such total length. header with such a total length.
The Magic Number field MUST be set to the RFC number to be assigned
to this document. This field is meant to further strengthen the
protocol to unambiguously distinguish any data supplied by an
application from Convert TLVs.
o Note to the RFC Editor: Please replace "the RFC number to be The Magic Number field MUST be set to 0x2263. This field is meant to
assigned to this document" with the hex representation of the RFC further strengthen the protocol to unambiguously distinguish any data
number assigned to this document. supplied by an application from Convert TLVs.
The Total Length field unambiguously marks the number of 32 bits The Total Length field unambiguously marks the number of 32-bit words
words that carry Convert TLVs in the beginning of the bytestream. that carry Convert TLVs in the beginning of the bytestream.
6.2. Convert TLVs 6.2. Convert TLVs
6.2.1. Generic Convert TLV Format 6.2.1. Generic Convert TLV Format
The Convert Protocol uses variable length messages that are encoded The Convert Protocol uses variable length messages that are encoded
using the generic TLV format depicted in Figure 14. using the generic TLV format depicted in Figure 14.
The length of all TLVs used by the Convert Protocol is always a The length of all TLVs used by the Convert Protocol is always a
multiple of four bytes. All TLVs are aligned on 32 bits boundaries. multiple of four bytes. All TLVs are aligned on 32-bit boundaries.
All TLV fields are encoded using the network byte order. All TLV fields are encoded using the network byte order.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Type | Length | Value ... | | Type | Length | Value ... |
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
// ... (optional) Value // // ... (optional) Value //
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 14: Convert Generic TLV Format Figure 14: Convert Generic TLV Format
The Length field covers Type, Length, and Value fields. It is The Length field covers Type, Length, and Value fields. It is
expressed in units of 32 bits words. If necessary, Value MUST be expressed in units of 32-bit words. If necessary, Value MUST be
padded with zeroes so that the length of the TLV is a multiple of 32 padded with zeroes so that the length of the TLV is a multiple of 32
bits. bits.
A given TLV MUST only appear once on a connection. If a Client A given TLV MUST only appear once on a connection. If a Client
receives two or more instances of the same TLV over a Convert receives two or more instances of the same TLV over a Convert
connection, it MUST reset the associated TCP connection. If a connection, it MUST reset the associated TCP connection. If a
Converter receives two or more instances of the same TLV over a Converter receives two or more instances of the same TLV over a
Convert connection, it MUST return a Malformed Message Error TLV and Convert connection, it MUST return a Malformed Message Error TLV and
close the associated TCP connection. close the associated TCP connection.
6.2.2. Summary of Supported Convert TLVs 6.2.2. Summary of Supported Convert TLVs
This document specifies the following Convert TLVs: This document specifies the following Convert TLVs:
+------+-----+----------+------------------------------------------+ +======+======+==========+==============================+
| Type | Hex | Length | Description | | Type | Hex | Length | Description |
+------+-----+----------+------------------------------------------+ +======+======+==========+==============================+
| 1 | 0x1 | 1 | Info TLV | | 1 | 0x1 | 1 | Info TLV |
| 10 | 0xA | Variable | Connect TLV | +------+------+----------+------------------------------+
| 20 | 0x14| Variable | Extended TCP Header TLV | | 10 | 0xA | Variable | Connect TLV |
| 21 | 0x15| Variable | Supported TCP Extensions TLV | +------+------+----------+------------------------------+
| 22 | 0x16| Variable | Cookie TLV | | 20 | 0x14 | Variable | Extended TCP Header TLV |
| 30 | 0x1E| Variable | Error TLV | +------+------+----------+------------------------------+
+------+-----+----------+------------------------------------------+ | 21 | 0x15 | Variable | Supported TCP Extensions TLV |
+------+------+----------+------------------------------+
| 22 | 0x16 | Variable | Cookie TLV |
+------+------+----------+------------------------------+
| 30 | 0x1E | Variable | Error TLV |
+------+------+----------+------------------------------+
Figure 15: The TLVs used by the Convert Protocol Table 1: The TLVs Used by the Convert Protocol
Type 0x0 is a reserved value. If a Client receives a TLV of type Type 0x0 is a reserved value. If a Client receives a TLV of type
0x0, it MUST reset the associated TCP connection. If a Converter 0x0, it MUST reset the associated TCP connection. If a Converter
receives a TLV of type 0x0, it MUST return an Unsupported Message receives a TLV of type 0x0, it MUST return an Unsupported Message
Error TLV and close the associated TCP connection. Error TLV and close the associated TCP connection.
The Client typically sends in the first connection it established The Client typically sends, in the first connection it established
with a Transport Converter the Info TLV (Section 6.2.3) to learn its with a Transport Converter, the Info TLV (Section 6.2.3) to learn its
capabilities. Assuming the Client is authorized to invoke the capabilities. Assuming the Client is authorized to invoke the
Transport Converter, the latter replies with the Supported TCP Transport Converter, the latter replies with the Supported TCP
Extensions TLV (Section 6.2.4). Extensions TLV (Section 6.2.4).
The Client can request the establishment of connections to servers by The Client can request the establishment of connections to Servers by
using the Connect TLV (Section 6.2.5). If the connection can be using the Connect TLV (Section 6.2.5). If the connection can be
established with the final server, the Transport Converter replies established with the final Server, the Transport Converter replies
with the Extended TCP Header TLV (Section 6.2.6). If not, the with the Extended TCP Header TLV (Section 6.2.6). If not, the
Transport Converter MUST return an Error TLV (Section 6.2.8) and then Transport Converter MUST return an Error TLV (Section 6.2.8) and then
closes the connection. The Transport Converter MUST NOT send an RST close the connection. The Transport Converter MUST NOT send an RST
immediately after the detection of an error to let the Error TLV immediately after the detection of an error to let the Error TLV
reach the Client. As explained later, the Client will anyway send an reach the Client. As explained later, the Client will send an RST
RST upon reception of the Error TLV. regardless upon reception of the Error TLV.
6.2.3. The Info TLV 6.2.3. The Info TLV
The Info TLV (Figure 16) is an optional TLV which can be sent by a The Info TLV (Figure 15) is an optional TLV that can be sent by a
Client to request the TCP extensions that are supported by a Client to request the TCP extensions that are supported by a
Transport Converter. It is typically sent on the first connection Transport Converter. It is typically sent on the first connection
that a Client establishes with a Transport Converter to learn its that a Client establishes with a Transport Converter to learn its
capabilities. Assuming a Client is entitled to invoke the Transport capabilities. Assuming a Client is entitled to invoke the Transport
Converter, the latter replies with the Supported TCP Extensions TLV Converter, the latter replies with the Supported TCP Extensions TLV
described in Section 6.2.4. described in Section 6.2.4.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Type=0x1 | Length | Zero | | Type=0x1 | Length | Zero |
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
Figure 16: The Info TLV Figure 15: The Info TLV
6.2.4. Supported TCP Extensions TLV 6.2.4. Supported TCP Extensions TLV
The Supported TCP Extensions TLV (Figure 17) is used by a Transport The Supported TCP Extensions TLV (Figure 16) is used by a Transport
Converter to announce the TCP options for which it provides a Converter to announce the TCP options for which it provides a
conversion service. A Transport Converter SHOULD include in this conversion service. A Transport Converter SHOULD include in this
list the TCP options that it supports in outgoing SYNs. list the TCP options that it supports in outgoing SYNs.
Each supported TCP option is encoded with its TCP option Kind listed Each supported TCP option is encoded with its TCP option Kind listed
in the "TCP Parameters" registry maintained by IANA. The Unassigned in the "Transmission Control Protocol (TCP) Parameters" registry
field MUST be set to zero by the Transport Converter and ignored by maintained by IANA [IANA-CONVERT]. The Unassigned field MUST be set
the Client. to zero by the Transport Converter and ignored by the Client.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Type=0x15 | Length | Unassigned | | Type=0x15 | Length | Unassigned |
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Kind #1 | Kind #2 | ... | | Kind #1 | Kind #2 | ... |
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
/ ... / / ... /
/ / / /
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 17: The Supported TCP Extensions TLV Figure 16: The Supported TCP Extensions TLV
TCP option Kinds 1 and 2 defined in [RFC0793] are supported by all TCP option Kinds 1 and 2 defined in [RFC0793] are supported by all
TCP implementations and thus MUST NOT appear in this list. TCP implementations and thus, MUST NOT appear in this list.
The list of Supported TCP Extensions is padded with 0 to end on a 32 The list of Supported TCP Extensions is padded with 0 to end on a
bits boundary. 32-bit boundary.
For example, if the Transport Converter supports Multipath TCP, For example, if the Transport Converter supports Multipath TCP,
Kind=30 will be present in the Supported TCP Extensions TLV that it Kind=30 will be present in the Supported TCP Extensions TLV that it
returns in response to Info TLV. returns in response to the Info TLV.
6.2.5. Connect TLV 6.2.5. Connect TLV
The Connect TLV (Figure 18) is used to request the establishment of a The Connect TLV (Figure 17) is used to request the establishment of a
connection via a Transport Converter. This connection can be from or connection via a Transport Converter. This connection can be from or
to a Client. to a Client.
The 'Remote Peer Port' and 'Remote Peer IP Address' fields contain The Remote Peer Port and Remote Peer IP Address fields contain the
the destination port number and IP address of the Server, for destination port number and IP address of the Server, for outgoing
outgoing connections. For incoming connections destined to a Client connections. For incoming connections destined to a Client serviced
serviced via a Transport Converter, these fields convey the source via a Transport Converter, these fields convey the source port number
port number and IP address of the SYN packet received by the and IP address of the SYN packet received by the Transport Converter
Transport Converter from the server. from the Server.
The Remote Peer IP Address MUST be encoded as an IPv6 address. IPv4 The Remote Peer IP Address MUST be encoded as an IPv6 address. IPv4
addresses MUST be encoded using the IPv4-Mapped IPv6 Address format addresses MUST be encoded using the IPv4-mapped IPv6 address format
defined in [RFC4291]. Further, Remote Peer IP address field MUST NOT defined in [RFC4291]. Further, the Remote Peer IP Address field MUST
include multicast, broadcast, and host loopback addresses [RFC6890]. NOT include multicast, broadcast, or host loopback addresses
If a Converter receives a Connect TLVs with such invalid addresses, [RFC6890]. If a Converter receives a Connect TLV with such invalid
it MUST reply with a Malformed Message Error TLV and close the addresses, it MUST reply with a Malformed Message Error TLV and close
associated TCP connection. the associated TCP connection.
We distinguish two types of Connect TLV based on their length: (1) We distinguish two types of Connect TLV based on their length: (1)
the Base Connect TLV has a length set to 5 (i.e., 20 bytes) and the Base Connect TLV has a length set to 5 (i.e., 20 bytes) and
contains a remote address and a remote port (Figure 18), (2) the contains a remote address and a remote port (Figure 17), and (2) the
Extended Connect TLV spans more than 20 bytes and also includes the Extended Connect TLV spans more than 20 bytes and also includes the
optional 'TCP Options' field (Figure 19). This field is used to optional TCP Options field (Figure 18). This field is used to
request the advertisement of specific TCP options to the server. request the advertisement of specific TCP options to the Server.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Type=0xA | Length | Remote Peer Port | | Type=0xA | Length | Remote Peer Port |
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| | | |
| Remote Peer IP Address (128 bits) | | Remote Peer IP Address (128 bits) |
| | | |
| | | |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 18: The Base Connect TLV Figure 17: The Base Connect TLV
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Type=0xA | Length | Remote Peer Port | | Type=0xA | Length | Remote Peer Port |
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| | | |
| Remote Peer IP Address (128 bits) | | Remote Peer IP Address (128 bits) |
| | | |
| | | |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
/ TCP Options (Variable) / / TCP Options (Variable) /
/ ... / / ... /
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 19: The Extended Connect TLV Figure 18: The Extended Connect TLV
The 'TCP Options' field is a variable length field that carries a The TCP Options field is a variable length field that carries a list
list of TCP option fields (Figure 20). Each TCP option field is of TCP option fields (Figure 19). Each TCP option field is encoded
encoded as a block of 2+n bytes where the first byte is the TCP as a block of 2+n bytes where the first byte is the TCP option Kind
option Kind and the second byte is the length of the TCP option as and the second byte is the length of the TCP option as specified in
specified in [RFC0793]. The minimum value for the TCP option Length [RFC0793]. The minimum value for the TCP option Length is 2. The
is 2. The TCP options that do not include a length sub-field, i.e., TCP options that do not include a length sub-field, i.e., option
option types 0 (EOL) and 1 (NOP) defined in [RFC0793] MUST NOT be types 0 (EOL) and 1 (NOP) defined in [RFC0793] MUST NOT be placed
placed inside the TCP options field of the Connect TLV. The optional inside the TCP options field of the Connect TLV. The optional Value
Value field contains the variable-length part of the TCP option. A field contains the variable-length part of the TCP option. A length
length of two indicates the absence of the Value field. The TCP of 2 indicates the absence of the Value field. The TCP options field
options field always ends on a 32 bits boundary after being padded always ends on a 32-bit boundary after being padded with zeros.
with zeros.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| TCPOpt kind | TCPOpt Length | Value (opt) | .... | | TCPOpt kind | TCPOpt Length | Value (opt) | .... |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| .... | | .... |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| ... | | ... |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 20: The TCP Options Field Figure 19: The TCP Options Field
Upon reception of a Base Connect TLV, and absent any policy (e.g., Upon reception of a Base Connect TLV, and absent any policy (e.g.,
rate-limit) or resource exhaustion conditions, a Transport Converter rate-limit) or resource exhaustion conditions, a Transport Converter
attempts to establish a connection to the address and port that it attempts to establish a connection to the address and port that it
contains. The Transport Converter MUST use by default the TCP contains. The Transport Converter MUST use by default the TCP
options that correspond to its local policy to establish this options that correspond to its local policy to establish this
connection. connection.
Upon reception of an Extended Connect TLV, a Transport Converter Upon reception of an Extended Connect TLV, a Transport Converter
first checks whether it supports the TCP Options listed in the 'TCP first checks whether or not it supports the TCP Options listed in the
Options' field. If not, it returns an error TLV set to "Unsupported TCP Options field. If not, it returns an error TLV set to
TCP Option" (Section 6.2.8). If the above check succeeded and absent "Unsupported TCP Option" (Section 6.2.8). If the above check
any rate limit policy or resource exhaustion conditions, a Transport succeeded, and absent any rate-limit policy or resource exhaustion
Converter MUST attempt to establish a connection to the address and conditions, a Transport Converter MUST attempt to establish a
port that it contains. It MUST include in the SYN that it sends to connection to the address and port that it contains. It MUST include
the Server the options listed in the 'TCP Options' sub-field and the in the SYN that it sends to the Server the options listed in the TCP
TCP options that it would have used according to its local policies. Options subfield and the TCP options that it would have used
For the TCP options that are included in the TCP Options field according to its local policies. For the TCP options that are
without an optional value, the Transport Converter MUST generate its included in the TCP Options field without an optional value, the
own value. For the TCP options that are included in the 'TCP Transport Converter MUST generate its own value. For the TCP options
Options' field with an optional value, it MUST copy the entire option that are included in the TCP Options field with an optional value, it
in the SYN sent to the remote server. This procedure is designed MUST copy the entire option in the SYN sent to the remote Server.
with TFO in mind. Particularly, this procedure allows to This procedure is designed with TFO in mind. Particularly, this
successfully exchange a TFO Cookie between the client and the server. procedure allows to successfully exchange a Fast Open Cookie between
See Section 7 for a detailed discussion of the different types of TCP the Client and the Server. See Section 7 for a detailed discussion
options. of the different types of TCP options.
The Transport Converter may refuse a Connect TLV request for various The Transport Converter may refuse a Connect TLV request for various
reasons (e.g., authorization failed, out of resources, invalid reasons (e.g., authorization failed, out of resources, invalid
address type, unsupported TCP option). An error message indicating address type, or unsupported TCP option). An error message
the encountered error is returned to the requesting Client indicating the encountered error is returned to the requesting Client
(Section 6.2.8). In order to prevent denial-of-service attacks, (Section 6.2.8). In order to prevent denial-of-service attacks,
error messages sent to a Client SHOULD be rate-limited. error messages sent to a Client SHOULD be rate-limited.
6.2.6. Extended TCP Header TLV 6.2.6. Extended TCP Header TLV
The Extended TCP Header TLV (Figure 21) is used by the Transport The Extended TCP Header TLV (Figure 20) is used by the Transport
Converter to return to the Client the TCP options that were returned Converter to return to the Client the TCP options that were returned
by the Server in the SYN+ACK packet. A Transport Converter MUST by the Server in the SYN+ACK packet. A Transport Converter MUST
return this TLV if the Client sent an Extended Connect TLV and the return this TLV if the Client sent an Extended Connect TLV and the
connection was accepted by the server. connection was accepted by the Server.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Type=0x14 | Length | Unassigned | | Type=0x14 | Length | Unassigned |
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
/ Returned Extended TCP header / / Returned Extended TCP header /
/ ... / / ... /
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 21: The Extended TCP Header TLV Figure 20: The Extended TCP Header TLV
The Returned Extended TCP header field is a copy of the TCP Options The Returned Extended TCP header field is a copy of the TCP Options
that were included in the SYN+ACK received by the Transport that were included in the SYN+ACK received by the Transport
Converter. Converter.
The Unassigned field MUST be set to zero by the sender and ignored by The Unassigned field MUST be set to zero by the sender and ignored by
the receiver. the receiver.
6.2.7. The Cookie TLV 6.2.7. The Cookie TLV
The Cookie TLV (Figure 22) is an optional TLV which is similar to the The Cookie TLV (Figure 21) is an optional TLV that is similar to the
TCP Fast Open Cookie [RFC7413]. A Transport Converter may want to TCP Fast Open Cookie [RFC7413]. A Transport Converter may want to
verify that a Client can receive the packets that it sends to prevent verify that a Client can receive the packets that it sends to prevent
attacks from spoofed addresses. This verification can be done by attacks from spoofed addresses. This verification can be done by
using a Cookie that is bound to, for example, the IP address(es) of using a Cookie that is bound to, for example, the IP address(es) of
the Client. This Cookie can be configured on the Client by means the Client. This Cookie can be configured on the Client by means
that are outside of this document or provided by the Transport that are outside of this document or provided by the Transport
Converter. Converter.
A Transport Converter that has been configured to use the optional A Transport Converter that has been configured to use the optional
Cookie TLV MUST verify the presence of this TLV in the payload of the Cookie TLV MUST verify the presence of this TLV in the payload of the
skipping to change at page 29, line 37 skipping to change at line 1360
If the received SYN did not contain a Cookie TLV, and cookie If the received SYN did not contain a Cookie TLV, and cookie
validation is required, the Transport Converter MAY compute a Cookie validation is required, the Transport Converter MAY compute a Cookie
bound to this Client address. In such case, the Transport Converter bound to this Client address. In such case, the Transport Converter
MUST return an Error TLV set to "Missing Cookie" and the computed MUST return an Error TLV set to "Missing Cookie" and the computed
Cookie and close the connection. The Client will react to this error Cookie and close the connection. The Client will react to this error
by first issuing a reset to terminate the connection. It also stores by first issuing a reset to terminate the connection. It also stores
the received Cookie in its cache and attempts to reestablish a new the received Cookie in its cache and attempts to reestablish a new
connection to the Transport Converter that includes the Cookie TLV. connection to the Transport Converter that includes the Cookie TLV.
The format of the Cookie TLV is shown in Figure 22. The format of the Cookie TLV is shown in Figure 21.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
| Type=0x16 | Length | Zero | | Type=0x16 | Length | Zero |
+---------------+---------------+-------------------------------+ +---------------+---------------+-------------------------------+
/ Opaque Cookie / / Opaque Cookie /
/ ... / / ... /
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 22: The Cookie TLV Figure 21: The Cookie TLV
6.2.8. Error TLV 6.2.8. Error TLV
The Error TLV (Figure 23) is meant to provide information about some The Error TLV (Figure 22) is meant to provide information about some
errors that occurred during the processing of a Convert message. errors that occurred during the processing of a Convert message.
This TLV has a variable length. Upon reception of an Error TLV, a This TLV has a variable length. Upon reception of an Error TLV, a
Client MUST reset the associated connection. Client MUST reset the associated connection.
An Error TLV can be included in the SYN+ACK or an ACK. An Error TLV can be included in the SYN+ACK or an ACK.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+----------------+--------------+ +---------------+---------------+----------------+--------------+
| Type=0x1E | Length | Error Code | Value | | Type=0x1E | Length | Error Code | Value |
+---------------+---------------+----------------+--------------+ +---------------+---------------+----------------+--------------+
// ... (optional) Value // // ... (optional) Value //
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 23: The Error TLV Figure 22: The Error TLV
Different types of errors can occur while processing Convert Different types of errors can occur while processing Convert
messages. Each error is identified by an Error Code represented as messages. Each error is identified by an Error Code represented as
an unsigned integer. Four classes of error codes are defined: an unsigned integer. Four classes of error codes are defined:
o Message validation and processing errors (0-31 range): returned Message validation and processing errors (0-31 range):
upon reception of an invalid message (including valid messages but Returned upon reception of an invalid message (including valid
with invalid or unknown TLVs). messages but with invalid or unknown TLVs).
o Client-side errors (32-63 range): the Client sent a request that Client-side errors (32-63 range):
could not be accepted by the Transport Converter (e.g., The Client sent a request that could not be accepted by the
unsupported operation). Transport Converter (e.g., unsupported operation).
o Converter-side errors (64-95 range): problems encountered on the Converter-side errors (64-95 range):
Transport Converter (e.g., lack of resources) which prevent it Problems encountered on the Transport Converter (e.g., lack of
from fulfilling the Client's request. resources) that prevent it from fulfilling the Client's request.
o Errors caused by the destination server (96-127 range): the final Errors caused by the destination Server (96-127 range):
destination could not be reached or it replied with a reset. The final destination could not be reached or it replied with a
reset.
The following error codes are defined in this document: The following error codes are defined in this document:
o Unsupported Version (0): The version number indicated in the fixed Unsupported Version (0):
header of a message received from a peer is not supported. The version number indicated in the fixed header of a message
received from a peer is not supported.
This error code MUST be generated by a peer (e.g. Transport This error code MUST be generated by a peer (e.g., Transport
Converter) when it receives a request having a version number that Converter) when it receives a request having a version number that
it does not support. it does not support.
The value field MUST be set to the version supported by the peer. The Value field MUST be set to the version supported by the peer.
When multiple versions are supported by the peer, it includes the When multiple versions are supported by the peer, it includes the
list of supported version in the value field; each version is list of supported versions in the Value field; each version is
encoded in 8 bits. The list of supported versions MUST be padded encoded in 8 bits. The list of supported versions MUST be padded
with zeros to end on a 32 bits boundary. with zeros to end on a 32-bit boundary.
Upon receipt of this error code, the remote peer (e.g., Client) Upon receipt of this error code, the remote peer (e.g., Client)
checks whether it supports one of the versions returned by the checks whether it supports one of the versions returned by the
peer. The highest common supported version MUST be used by the peer. The highest commonly supported version number MUST be used
remote peer in subsequent exchanges with the peer. by the remote peer in subsequent exchanges with the peer.
o Malformed Message (1): This error code is sent to indicate that a Malformed Message (1):
message received from a peer cannot be successfully parsed and This error code is sent to indicate that a message received from a
validated. peer cannot be successfully parsed and validated.
Typically, this error code is sent by the Transport Converter if Typically, this error code is sent by the Transport Converter if
it receives a Connect TLV enclosing a multicast, broadcast, or it receives a Connect TLV enclosing a multicast, broadcast, or
loopback IP address. loopback IP address.
To ease troubleshooting, the value field MUST echo the received To ease troubleshooting, the Value field MUST echo the received
message using the format depicted in Figure 24. This format message using the format depicted in Figure 23. This format
allows to keep the original alignment of the message that allows keeping the original alignment of the message that
triggered the error. triggered the error.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+----------------+--------------+ +---------------+---------------+----------------+--------------+
| Type=0x1E | Length | Error Code | Zeros | | Type=0x1E | Length | Error Code | Zeros |
+---------------+---------------+----------------+--------------+ +---------------+---------------+----------------+--------------+
// Echo the message which triggered the error // // Echo the message that triggered the error //
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Figure 24: Error TLV to ease Message Correlation Figure 23: Error TLV to Ease Message Correlation
o Unsupported Message (2): This error code is sent to indicate that Unsupported Message (2):
a message type received from a Client is not supported. This error code is sent to indicate that a message type received
from a Client is not supported.
To ease troubleshooting, the value field MUST echo the received To ease troubleshooting, the Value field MUST echo the received
message using the format shown in Figure 24. message using the format shown in Figure 23.
o Missing Cookie (3): If a Transport Converter requires the Missing Cookie (3):
utilization of Cookies to prevent spoofing attacks and a Cookie If a Transport Converter requires the utilization of Cookies to
TLV was not included in the Convert message, the Transport prevent spoofing attacks and a Cookie TLV was not included in the
Converter MUST return this error to the requesting client only if Convert message, the Transport Converter MUST return this error to
it computes a cookie for this client. The first byte of the value the requesting Client only if it computes a cookie for this
field MUST be set to zero and the remaining bytes of the Error TLV Client. The first byte of the Value field MUST be set to zero and
contain the Cookie computed by the Transport Converter for this the remaining bytes of the Error TLV contain the Cookie computed
Client. by the Transport Converter for this Client.
A Client which receives this error code SHOULD cache the received A Client that receives this error code SHOULD cache the received
Cookie and include it in subsequent Convert messages sent to that Cookie and include it in subsequent Convert messages sent to that
Transport Converter. Transport Converter.
o Not Authorized (32): This error code indicates that the Transport Not Authorized (32):
Converter refused to create a connection because of a lack of This error code indicates that the Transport Converter refused to
authorization (e.g., administratively prohibited, authorization create a connection because of a lack of authorization (e.g.,
failure, invalid Cookie TLV). The Value field MUST be set to administratively prohibited, authorization failure, or invalid
zero. Cookie TLV). The Value field MUST be set to zero.
This error code MUST be sent by the Transport Converter when a This error code MUST be sent by the Transport Converter when a
request cannot be successfully processed because the authorization request cannot be successfully processed because the authorization
failed. failed.
o Unsupported TCP Option (33): A TCP option that the Client Unsupported TCP Option (33):
requested to advertise to the final Server cannot be safely used. A TCP option that the Client requested to advertise to the final
Server cannot be safely used.
The Value field is set to the type of the unsupported TCP option. The Value field is set to the type of the unsupported TCP option.
If several unsupported TCP options were specified in the Connect If several unsupported TCP options were specified in the Connect
TLV, then the list of unsupported TCP options is returned. The TLV, then the list of unsupported TCP options is returned. The
list of unsupported TCP options MUST be padded with zeros to end list of unsupported TCP options MUST be padded with zeros to end
on a 32 bits boundary. on a 32-bit boundary.
o Resource Exceeded (64): This error indicates that the Transport Resource Exceeded (64):
Converter does not have enough resources to perform the request. This error indicates that the Transport Converter does not have
enough resources to perform the request.
This error MUST be sent by the Transport Converter when it does This error MUST be sent by the Transport Converter when it does
not have sufficient resources to handle a new connection. The not have sufficient resources to handle a new connection. The
Transport Converter may indicate in the Value field the suggested Transport Converter may indicate in the Value field the suggested
delay (in seconds) that the Client SHOULD wait before soliciting delay (in seconds) that the Client SHOULD wait before soliciting
the Transport Converter for a new proxied connection. A Value of the Transport Converter for a new proxied connection. A Value of
zero corresponds to a default delay of at least 30 seconds. zero corresponds to a default delay of at least 30 seconds.
o Network Failure (65): This error indicates that the Transport Network Failure (65):
Converter is experiencing a network failure to proxy the request. This error indicates that the Transport Converter is experiencing
a network failure to proxy the request.
The Transport Converter MUST send this error code when it The Transport Converter MUST send this error code when it
experiences forwarding issues to proxy a connection. The experiences forwarding issues to proxy a connection. The
Transport Converter may indicate in the Value field the suggested Transport Converter may indicate in the Value field the suggested
delay (in seconds) that the Client SHOULD wait before soliciting delay (in seconds) that the Client SHOULD wait before soliciting
the Transport Converter for a new proxied connection. A Value of the Transport Converter for a new proxied connection. A Value of
zero corresponds to a default delay of at least 30 seconds. zero corresponds to a default delay of at least 30 seconds.
o Connection Reset (96): This error indicates that the final Connection Reset (96):
destination responded with an RST segment. The Value field MUST This error indicates that the final destination responded with an
be set to zero. RST segment. The Value field MUST be set to zero.
o Destination Unreachable (97): This error indicates that an ICMP Destination Unreachable (97):
message indicating a hard error (e.g., destination unreachable, This error indicates that an ICMP message indicating a hard error
port unreachable, or network unreachable) was received by the (e.g., destination unreachable, port unreachable, or network
Transport Converter. The Value field MUST echo the Code field of unreachable) was received by the Transport Converter. The Value
the received ICMP message. field MUST echo the Code field of the received ICMP message.
As a reminder, TCP implementations are supposed to act on an ICMP As a reminder, TCP implementations are supposed to act on an ICMP
error message passed up from the IP layer, directing it to the error message passed up from the IP layer, directing it to the
connection that triggered the error using the demultiplexing connection that triggered the error using the demultiplexing
information included in the payload of that ICMP message. Such information included in the payload of that ICMP message. Such a
demultiplexing issue does not apply for handling the "Destination demultiplexing issue does not apply for handling the "Destination
Unreachable" Error TLV because the error is sent in-band. For Unreachable" Error TLV because the error is sent in-band. For
this reason, the payload of the ICMP message is not echoed in the this reason, the payload of the ICMP message is not echoed in the
Destination Unreachable Error TLV. Destination Unreachable Error TLV.
Figure 25 summarizes the different error codes. Table 2 summarizes the different error codes.
+-------+------+-----------------------------------------------+ +=======+======+=========================+
| Error | Hex | Description | | Error | Hex | Description |
+-------+------+-----------------------------------------------+ +=======+======+=========================+
| 0 | 0x00 | Unsupported Version | | 0 | 0x00 | Unsupported Version |
| 1 | 0x01 | Malformed Message | +-------+------+-------------------------+
| 2 | 0x02 | Unsupported Message | | 1 | 0x01 | Malformed Message |
| 3 | 0x03 | Missing Cookie | +-------+------+-------------------------+
| 32 | 0x20 | Not Authorized | | 2 | 0x02 | Unsupported Message |
| 33 | 0x21 | Unsupported TCP Option | +-------+------+-------------------------+
| 64 | 0x40 | Resource Exceeded | | 3 | 0x03 | Missing Cookie |
| 65 | 0x41 | Network Failure | +-------+------+-------------------------+
| 96 | 0x60 | Connection Reset | | 32 | 0x20 | Not Authorized |
| 97 | 0x61 | Destination Unreachable | +-------+------+-------------------------+
+-------+------+-----------------------------------------------+ | 33 | 0x21 | Unsupported TCP Option |
+-------+------+-------------------------+
| 64 | 0x40 | Resource Exceeded |
+-------+------+-------------------------+
| 65 | 0x41 | Network Failure |
+-------+------+-------------------------+
| 96 | 0x60 | Connection Reset |
+-------+------+-------------------------+
| 97 | 0x61 | Destination Unreachable |
+-------+------+-------------------------+
Figure 25: Convert Error Values Table 2: Convert Error Values
7. Compatibility of Specific TCP Options with the Conversion Service 7. Compatibility of Specific TCP Options with the Conversion Service
In this section, we discuss how several deployed standard track TCP In this section, we discuss how several deployed Standards Track TCP
options can be supported through the Convert Protocol. The other TCP options can be supported through the Convert Protocol. The other TCP
options will be discussed in other documents. options will be discussed in other documents.
7.1. Base TCP Options 7.1. Base TCP Options
Three TCP options were initially defined in [RFC0793]: End-of-Option Three TCP options were initially defined in [RFC0793]: End-of-Option
List (Kind=0), No-Operation (Kind=1) and Maximum Segment Size List (Kind=0), No-Operation (Kind=1), and Maximum Segment Size
(Kind=2). The first two options are mainly used to pad the TCP (Kind=2). The first two options are mainly used to pad the TCP
header. There is no reason for a client to request a Transport header. There is no reason for a Client to request a Transport
Converter to specifically send these options towards the final Converter to specifically send these options towards the final
destination. destination.
The Maximum Segment Size option (Kind=2) is used by a host to The Maximum Segment Size option (Kind=2) is used by a host to
indicate the largest segment that it can receive over each indicate the largest segment that it can receive over each
connection. This value is function of the stack that terminates the connection. This value is a function of the stack that terminates
TCP connection. There is no reason for a Client to request a the TCP connection. There is no reason for a Client to request a
Transport Converter to advertise a specific MSS value to a remote Transport Converter to advertise a specific Maximum Segment Size
server. (MSS) value to a remote Server.
A Transport Converter MUST ignore options with Kind=0, 1 or 2 if they A Transport Converter MUST ignore options with Kind=0, 1, or 2 if
appear in a Connect TLV. It MUST NOT announce them in a Supported they appear in a Connect TLV. It MUST NOT announce them in a
TCP Extensions TLV. Supported TCP Extensions TLV.
7.2. Window Scale (WS) 7.2. Window Scale (WS)
The Window Scale (WS) option (Kind=3) is defined in [RFC7323]. As The Window Scale (WS) option (Kind=3) is defined in [RFC7323]. As
for the MSS option, the window scale factor that is used for a for the MSS option, the window scale factor that is used for a
connection strongly depends on the TCP stack that handles the connection strongly depends on the TCP stack that handles the
connection. When a Transport Converter opens a TCP connection connection. When a Transport Converter opens a TCP connection
towards a remote server on behalf of a Client, it SHOULD use a WS towards a remote Server on behalf of a Client, it SHOULD use a WS
option with a scaling factor that corresponds to the configuration of option with a scaling factor that corresponds to the configuration of
its stack. A local configuration MAY allow for WS option in the its stack. A local configuration MAY allow for a WS option in the
proxied message to be function of the scaling factor of the incoming proxied message to be a function of the scaling factor of the
connection. incoming connection.
There is no benefit from a deployment viewpoint in enabling a Client From a deployment viewpoint, there is no benefit in enabling a Client
of a Transport Converter to specifically request the utilization of of a Transport Converter to specifically request the utilization of
the WS option (Kind=3) with a specific scaling factor towards a the WS option (Kind=3) with a specific scaling factor towards a
remote Server. For this reason, a Transport Converter MUST ignore remote Server. For this reason, a Transport Converter MUST ignore
option Kind=3 if it appears in a Connect TLV. It MUST NOT announce option Kind=3 if it appears in a Connect TLV. The Transport
it in a Supported TCP Extensions TLV. Converter MUST NOT announce a WS option (Kind=3) in a Supported TCP
Extensions TLV.
7.3. Selective Acknowledgments 7.3. Selective Acknowledgments
Two distinct TCP options were defined to support selective Two distinct TCP options were defined to support Selective
acknowledgments in [RFC2018]. This first one, SACK Permitted Acknowledgment (SACK) in [RFC2018]. This first one, SACK-Permitted
(Kind=4), is used to negotiate the utilization of selective (Kind=4), is used to negotiate the utilization of Selective
acknowledgments during the three-way handshake. The second one, SACK Acknowledgments during the three-way handshake. The second one, SACK
(Kind=5), carries the selective acknowledgments inside regular (Kind=5), carries the Selective Acknowledgments inside regular
segments. segments.
The SACK Permitted option (Kind=4) MAY be advertised by a Transport The SACK-Permitted option (Kind=4) MAY be advertised by a Transport
Converter in the Supported TCP Extensions TLV. Clients connected to Converter in the Supported TCP Extensions TLV. Clients connected to
this Transport Converter MAY include the SACK Permitted option in the this Transport Converter MAY include the SACK-Permitted option in the
Connect TLV. Connect TLV.
The SACK option (Kind=5) cannot be used during the three-way The SACK option (Kind=5) cannot be used during the three-way
handshake. For this reason, a Transport Converter MUST ignore option handshake. For this reason, a Transport Converter MUST ignore option
Kind=5 if it appears in a Connect TLV. It MUST NOT announce it in a Kind=5 if it appears in a Connect TLV. It MUST NOT announce it in a
TCP Supported Extensions TLV. TCP Supported Extensions TLV.
7.4. Timestamp 7.4. Timestamp
The Timestamp option [RFC7323] can be used during the three-way The Timestamp option [RFC7323] can be used during the three-way
handshake to negotiate the utilization of timestamps during the TCP handshake to negotiate the utilization of timestamps during the TCP
connection. It is notably used to improve round-trip-time connection. It is notably used to improve round-trip-time
estimations and to provide protection against wrapped sequence estimations and to provide Protection Against Wrapped Sequences
numbers (PAWS). As for the WS option, the timestamps are a property (PAWS). As for the WS option, the timestamps are a property of a
of a connection and there is limited benefit in enabling a client to connection and there is limited benefit in enabling a Client to
request a Transport Converter to use the timestamp option when request a Transport Converter to use the timestamp option when
establishing a connection to a remote server. Furthermore, the establishing a connection to a remote Server. Furthermore, the
timestamps that are used by TCP stacks are specific to each stack and timestamps that are used by TCP stacks are specific to each stack and
there is no benefit in enabling a client to specify the timestamp there is no benefit in enabling a Client to specify the timestamp
value that a Transport Converter could use to establish a connection value that a Transport Converter could use to establish a connection
to a remote server. to a remote Server.
A Transport Converter MAY advertise the Timestamp option (Kind=8) in A Transport Converter MAY advertise the Timestamp option (Kind=8) in
the TCP Supported Extensions TLV. The clients connected to this the TCP Supported Extensions TLV. The Clients connected to this
Transport Converter MAY include the Timestamp option in the Connect Transport Converter MAY include the Timestamp option in the Connect
TLV but without any timestamp. TLV but without any timestamp.
7.5. Multipath TCP 7.5. Multipath TCP
The Multipath TCP options are defined in [RFC6824]. [RFC6824] The Multipath TCP options are defined in [RFC8684], which defines one
defines one variable length TCP option (Kind=30) that includes a sub- variable length TCP option (Kind=30) that includes a sub-type field
type field to support several Multipath TCP options. There are to support several Multipath TCP options. There are several
several operational use cases where clients would like to use operational use cases where Clients would like to use Multipath TCP
Multipath TCP through a Transport Converter [IETFJ16]. However, none through a Transport Converter [IETFJ16]. However, none of these use
of these use cases require the Client to specify the content of the cases require the Client to specify the content of the Multipath TCP
Multipath TCP option that the Transport Converter should send to a option that the Transport Converter should send to a remote Server.
remote server.
A Transport Converter which supports Multipath TCP conversion service A Transport Converter that supports Multipath TCP conversion service
MUST advertise the Multipath TCP option (Kind=30) in the Supported MUST advertise the Multipath TCP option (Kind=30) in the Supported
TCP Extensions TLV. Clients serviced by this Transport Converter may TCP Extensions TLV. Clients serviced by this Transport Converter may
include the Multipath TCP option in the Connect TLV but without any include the Multipath TCP option in the Connect TLV but without any
content. content.
7.6. TCP Fast Open 7.6. TCP Fast Open
The TCP Fast Open cookie option (Kind=34) is defined in [RFC7413]. The TCP Fast Open Cookie option (Kind=34) is defined in [RFC7413].
There are two different usages of this option that need to be There are two different usages of this option that need to be
supported by Transport Converters. The first utilization of the TCP supported by Transport Converters. The first utilization of the TCP
Fast Open cookie option is to request a cookie from the server. In Fast Open Cookie option is to request a cookie from the Server. In
this case, the option is sent with an empty cookie by the client and this case, the option is sent with an empty cookie by the Client, and
the server returns the cookie. The second utilization of the TCP the Server returns the cookie. The second utilization of the TCP
Fast Open cookie option is to send a cookie to the server. In this Fast Open Cookie option is to send a cookie to the Server. In this
case, the option contains a cookie. case, the option contains a cookie.
A Transport Converter MAY advertise the TCP Fast Open cookie option A Transport Converter MAY advertise the TCP Fast Open Cookie option
(Kind=34) in the Supported TCP Extensions TLV. If a Transport (Kind=34) in the Supported TCP Extensions TLV. If a Transport
Converter has advertised the support for TCP Fast Open in its Converter has advertised the support for TCP Fast Open in its
Supported TCP Extensions TLV, it needs to be able to process two Supported TCP Extensions TLV, it needs to be able to process two
types of Connect TLV. types of Connect TLV.
If such a Transport Converter receives a Connect TLV with the TCP If such a Transport Converter receives a Connect TLV with the TCP
Fast Open cookie option that does not contain a cookie, it MUST add Fast Open Cookie option that does not contain a cookie, it MUST add
an empty TCP Fast Open cookie option in the SYN sent to the remote an empty TCP Fast Open Cookie option in the SYN sent to the remote
server. If the remote server supports TFO, it responds with a SYN- Server. If the remote Server supports TFO, it responds with a SYN-
ACK according to the procedure in Section 4.1.2 of [RFC7413]. This ACK according to the procedure in Section 4.1.2 of [RFC7413]. This
SYN-ACK may contain a Fast Open option with a cookie. Upon receipt SYN-ACK may contain a Fast Open option with a cookie. Upon receipt
of the SYN-ACK by the Converter, it relays Fast Open option with the of the SYN-ACK by the Converter, it relays the Fast Open option with
cookie to the Client. the cookie to the Client.
If such a Transport Converter receives a Connect TLV with the TCP If such a Transport Converter receives a Connect TLV with the TCP
Fast Open cookie option that contains a cookie, it MUST copy the TCP Fast Open Cookie option that contains a cookie, it MUST copy the TCP
Fast Open cookie option in the SYN sent to the remote server. Fast Open Cookie option in the SYN sent to the remote Server.
7.7. TCP-AO 7.7. TCP-AO
TCP-AO [RFC5925] provides a technique to authenticate all the packets The TCP Authentication Option (TCP-AO) [RFC5925] provides a technique
exchanged over a TCP connection. Given the nature of this extension, to authenticate all the packets exchanged over a TCP connection.
it is unlikely that the applications that require their packets to be Given the nature of this extension, it is unlikely that the
authenticated end-to-end would want their connections to pass through applications that require their packets to be authenticated end to
a converter. For this reason, we do not recommend the support of the end would want their connections to pass through a converter. For
TCP-AO option by Transport Converters. The only use cases where it this reason, we do not recommend the support of the TCP-AO by
could make sense to combine TCP-AO and the solution in this document Transport Converters. The only use cases where it could make sense
are those where the TCP-AO-NAT extension [RFC6978] is in use. to combine TCP-AO and the solution in this document are those where
the TCP-AO-NAT extension [RFC6978] is in use.
A Transport Converter MUST NOT advertise the TCP-AO option (Kind=29) A Transport Converter MUST NOT advertise the TCP-AO (Kind=29) in the
in the Supported TCP Extensions TLV. If a Transport Converter Supported TCP Extensions TLV. If a Transport Converter receives a
receives a Connect TLV that contains the TCP-AO option, it MUST Connect TLV that contains the TCP-AO, it MUST reject the
reject the establishment of the connection with error code set to establishment of the connection with error code set to "Unsupported
"Unsupported TCP Option", except if the TCP-AO-NAT option is used. TCP Option", except if the TCP-AO-NAT option is used. Nevertheless,
Nevertheless, given that TCP-AO-NAT is Experimental, its usage is not given that TCP-AO-NAT is Experimental, its usage is not currently
currently defined and must be specified by some other document before defined and must be specified by some other document before it can be
it can be used. used.
8. Interactions with Middleboxes 8. Interactions with Middleboxes
The Convert Protocol is designed to be used in networks that do not The Convert Protocol is designed to be used in networks that do not
contain middleboxes that interfere with TCP. Under such conditions, contain middleboxes that interfere with TCP. Under such conditions,
it is assumed that the network provider ensures that all involved on- it is assumed that the network provider ensures that all involved on-
path nodes are not breaking TCP signals (e.g., strip TCP options, path nodes are not breaking TCP signals (e.g., strip TCP options,
discard some SYNs, etc.). discard some SYNs, etc.).
Nevertheless, and in order to allow for a robust service, this Nevertheless, and in order to allow for a robust service, this
skipping to change at page 37, line 27 skipping to change at line 1747
stop to use this Transport Converter given the middlebox stop to use this Transport Converter given the middlebox
interference. interference.
Consider now a middlebox that drops SYN/ACKs with a payload. The Consider now a middlebox that drops SYN/ACKs with a payload. The
Client won't be able to establish a connection via the Transport Client won't be able to establish a connection via the Transport
Converter. The case of a middlebox that removes the payload of Converter. The case of a middlebox that removes the payload of
SYN+ACKs or from the packet that follows the SYN+ACK (but not the SYN+ACKs or from the packet that follows the SYN+ACK (but not the
payload of SYN) can be detected by a Client. This is hinted by the payload of SYN) can be detected by a Client. This is hinted by the
absence of a valid Convert message in the response. absence of a valid Convert message in the response.
As explained in [RFC7413], some CGNs (Carrier Grade NATs) can affect As explained in [RFC7413], some Carrier Grade NATs (CGNs) can affect
the operation of TFO if they assign different IP addresses to the the operation of TFO if they assign different IP addresses to the
same end host. Such CGNs could affect the operation of the cookie same end host. Such CGNs could affect the operation of the cookie
validation used by the Convert Protocol. As a reminder CGNs, enabled validation used by the Convert Protocol. As a reminder, CGNs that
on the path between a Client and a Transport Converter, must adhere are enabled on the path between a Client and a Transport Converter
to the address preservation defined in [RFC6888]. See also the must adhere to the address preservation defined in [RFC6888]. See
discussion in Section 7.1 of [RFC7413]. also the discussion in Section 7.1 of [RFC7413].
9. Security Considerations 9. Security Considerations
An implementation MUST check that the Convert TLVs are properly An implementation MUST check that the Convert TLVs are properly
framed within the boundary indicated by the Total Length in the fixed framed within the boundary indicated by the Total Length in the fixed
header (Section 6.1). header (Section 6.1).
Additional security considerations are discussed in the following Additional security considerations are discussed in the following
sub-sections. subsections.
9.1. Privacy & Ingress Filtering 9.1. Privacy & Ingress Filtering
The Transport Converter may have access to privacy-related The Transport Converter may have access to privacy-related
information (e.g., subscriber credentials). The Transport Converter information (e.g., subscriber credentials). The Transport Converter
is designed to not leak such sensitive information outside a local is designed to not leak such sensitive information outside a local
domain. domain.
Given its function and location in the network, a Transport Converter Given its function and location in the network, a Transport Converter
is in a position to observe all packets that it processes, to include is in a position to observe all packets that it processes, to include
payloads and meta-data; and has the ability to profile and conduct payloads and metadata, and has the ability to profile and conduct
some traffic analysis of user behavior. The Transport Converter MUST some traffic analysis of user behavior. The Transport Converter MUST
be as protected as a core IP router (e.g., Section 10 of [RFC1812]). be as protected as a core IP router (e.g., Section 10 of [RFC1812]).
Furthermore, ingress filtering policies MUST be enforced at the Furthermore, ingress filtering policies MUST be enforced at the
network boundaries [RFC2827]. network boundaries [RFC2827].
This document assumes that all network attachments are managed by the This document assumes that all network attachments are managed by the
same administrative entity. Therefore, enforcing anti-spoofing same administrative entity. Therefore, enforcing anti-spoofing
filters at these network is a guard that hosts are not sending filters at these networks is a guard that hosts are not sending
traffic with spoofed source IP addresses. traffic with spoofed source IP addresses.
9.2. Authentication and Authorization Considerations 9.2. Authentication and Authorization Considerations
The Convert Protocol is RECOMMENDED to be used in a managed network The Convert Protocol is RECOMMENDED for use in a managed network
where end hosts can be securely identified by their IP address. If where end hosts can be securely identified by their IP address. If
such control is not exerted and there is a more open network such control is not exerted and there is a more open network
environment, a strong mutual authentication scheme MUST be defined to environment, a strong mutual authentication scheme MUST be defined to
use the Convert Protocol. use the Convert Protocol.
One possibility for mutual authentication is to use TLS to perform One possibility for mutual authentication is to use TLS to perform
mutual authentication between the client and the Converter. That is, mutual authentication between the Client and the Converter. That is,
use TLS when a Client retrieves a Cookie from the Converter and rely use TLS when a Client retrieves a Cookie from the Converter and rely
on certificate-based client authentication, pre-shared key based on certificate-based, pre-shared key-based [RFC4279], or raw public
[RFC4279] or raw public key based client authentication [RFC7250] to key-based Client authentication [RFC7250] to secure this connection.
secure this connection. If the authentication succeeds, the If the authentication succeeds, the Converter returns a cookie to the
Converter returns a cookie to the Client. Subsequent Connect Client. Subsequent Connect messages will be authorized as a function
messages will be authorized as a function of the content of the of the content of the Cookie TLV. An attacker from within the
Cookie TLV. An attacker from within the network between a Client and network between a Client and a Transport Converter may intercept the
a Transport Converter may intercept the Cookie and use it to be Cookie and use it to be granted access to the conversion service.
granted access to the conversion service. Such attack is only Such an attack is only possible if the attacker spoofs the IP address
possible if the attacker spoofs the IP address of the Client and the of the Client and the network does not filter packets with source-
network does not filter packets with source spoofed IP addresses. spoofed IP addresses.
The operator that manages the various network attachments (including The operator that manages the various network attachments (including
the Transport Converters) has various options for enforcing the Transport Converters) has various options for enforcing
authentication and authorization policies. For example, a non- authentication and authorization policies. For example, a non-
exhaustive list of methods to achieve authorization is provided exhaustive list of methods to achieve authorization is provided
hereafter: hereafter:
o The network provider may enforce a policy based on the * The network provider may enforce a policy based on the
International Mobile Subscriber Identity (IMSI) to verify that a International Mobile Subscriber Identity (IMSI) to verify that a
user is allowed to benefit from the TCP converter service. If user is allowed to benefit from the TCP converter service. If
that authorization fails, the Packet Data Protocol (PDP) context/ that authorization fails, the Packet Data Protocol (PDP) context/
bearer will not be mounted. This method does not require any bearer will not be mounted. This method does not require any
interaction with the Transport Converter for authorization interaction with the Transport Converter for authorization
matters. matters.
o The network provider may enforce a policy based upon Access * The network provider may enforce a policy based upon Access
Control Lists (ACLs), e.g., at a Broadband Network Gateway (BNG) Control Lists (ACLs), e.g., at a Broadband Network Gateway (BNG)
to control the hosts that are authorized to communicate with a to control the hosts that are authorized to communicate with a
Transport Converter. These ACLs may be installed as a result of Transport Converter. These ACLs may be installed as a result of
RADIUS exchanges, e.g., [I-D.boucadair-radext-tcpm-converter]. RADIUS exchanges, e.g., [TCPM-CONVERTER]. This method does not
This method does not require any interaction with the Transport require any interaction with the Transport Converter for
Converter for authorization matters. authorization matters.
o A device that embeds a Transport Converter may also host a RADIUS * A device that embeds a Transport Converter may also host a RADIUS
client that will solicit an AAA server to check whether Client that will solicit a AAA Server to check whether or not
connections received from a given source IP address are authorized connections received from a given source IP address are authorized
or not [I-D.boucadair-radext-tcpm-converter]. [TCPM-CONVERTER].
A first safeguard against the misuse of Transport Converter resources A first safeguard against the misuse of Transport Converter resources
by illegitimate users (e.g., users with access networks that are not by illegitimate users (e.g., users with access networks that are not
managed by the same provider that operates the Transport Converter) managed by the same provider that operates the Transport Converter)
is the Transport Converter to reject Convert connections received in is the Transport Converter to reject Convert connections received in
the external realm. Only Convert connections received in the the external realm. Only Convert connections received in the
internal realm of a Transport Converter will be accepted. internal realm of a Transport Converter will be accepted.
In deployments where network-assisted connections are not allowed In deployments where network-assisted connections are not allowed
between hosts of a domain (i.e., hairpinning), the Converter may be between hosts of a domain (i.e., hairpinning), the Converter may be
instructed to discard such connections. Hairpinned connections are instructed to discard such connections. Hairpinned connections are
thus rejected by the Transport Converter by returning an Error TLV thus rejected by the Transport Converter by returning an Error TLV
set to "Not Authorized". Absent explicit configuration otherwise, set to "Not Authorized". Otherwise, absent explicit configuration,
hairpinning is enabled by the Converter (see Figure 26. hairpinning is enabled by the Converter (see Figure 24).
<===Network Provider===> <===Network Provider===>
+----+ from X1:x1 to X2':x2' +-----+ X1':x1' +----+ from X1:x1 to X2':x2' +-----+ X1':x1'
| C1 |>>>>>>>>>>>>>>>>>>>>>>>>>>>>>--+--- | C1 |>>>>>>>>>>>>>>>>>>>>>>>>>>>>>--+---
+----+ | v | +----+ | v |
| v | | v |
| v | | v |
| v | | v |
+----+ from X1':x1' to X2:x2 | v | X2':x2' +----+ from X1':x1' to X2:x2 | v | X2':x2'
| C2 |<<<<<<<<<<<<<<<<<<<<<<<<<<<<<--+--- | C2 |<<<<<<<<<<<<<<<<<<<<<<<<<<<<<--+---
+----+ +-----+ +----+ +-----+
Converter Converter
Note: X2':x2' may be equal to Note: X2':x2' may be equal to
X2:x2 X2:x2
Figure 26: Hairpinning Example Figure 24: Hairpinning Example
9.3. Denial of Service 9.3. Denial of Service
Another possible risk is the amplification attacks since a Transport Another possible risk is amplification attacks, since a Transport
Converter sends a SYN towards a remote Server upon reception of a SYN Converter sends a SYN towards a remote Server upon reception of a SYN
from a Client. This could lead to amplification attacks if the SYN from a Client. This could lead to amplification attacks if the SYN
sent by the Transport Converter were larger than the SYN received sent by the Transport Converter were larger than the SYN received
from the Client or if the Transport Converter retransmits the SYN. from the Client, or if the Transport Converter retransmits the SYN.
To mitigate such attacks, the Transport Converter SHOULD rate limit To mitigate such attacks, the Transport Converter SHOULD rate-limit
the number of pending requests for a given Client. It SHOULD also the number of pending requests for a given Client. It SHOULD also
avoid sending to remote Servers SYNs that are significantly longer avoid sending SYNs that are significantly longer than the SYN
than the SYN received from the Client. Finally, the Transport received from the Client, to remote Servers. Finally, the Transport
Converter SHOULD only retransmit a SYN to a Server after having Converter SHOULD only retransmit a SYN to a Server after having
received a retransmitted SYN from the corresponding Client. Means to received a retransmitted SYN from the corresponding Client. Means to
protect against SYN flooding attacks should also be enabled (e.g., protect against SYN flooding attacks should also be enabled (e.g.,
Section 3 of [RFC4987]). Section 3 of [RFC4987]).
Attacks from within the network between a Client and a Transport Attacks from within the network between a Client and a Transport
Converter (including attacks that change the protocol version) are Converter (including attacks that change the protocol version) are
yet another threat. Means to ensure that illegitimate nodes cannot yet another threat. Means to ensure that illegitimate nodes cannot
connect to a network should be implemented. connect to a network should be implemented.
9.4. Traffic Theft 9.4. Traffic Theft
Traffic theft is a risk if an illegitimate Converter is inserted in Traffic theft is a risk if an illegitimate Converter is inserted in
the path. Indeed, inserting an illegitimate Converter in the the path. Indeed, inserting an illegitimate Converter in the
forwarding path allows traffic interception and can therefore provide forwarding path allows traffic interception and can therefore provide
access to sensitive data issued by or destined to a host. Converter access to sensitive data issued by or destined to a host. Converter
discovery and configuration are out of scope of this document. discovery and configuration are out of scope of this document.
9.5. Logging 9.5. Logging
If the Converter is configured to behave in the address sharing mode If the Converter is configured to behave in the address-sharing mode
(Section 4.4.2), the logging recommendations discussed in Section 4 (Section 4.4.2), the logging recommendations discussed in Section 4
of [RFC6888] need to be considered. Security-related issues of [RFC6888] need to be considered. Security-related issues
encountered in address sharing environments are documented in encountered in address-sharing environments are documented in
Section 13 of [RFC6269]. Section 13 of [RFC6269].
10. IANA Considerations 10. IANA Considerations
Note to the RFC Editor: Please replace "THISRFC" in the following
sub-sections with the RFC number to be assigned to this document.
10.1. Convert Service Name 10.1. Convert Service Name
IANA is requested to assign a service name for the Convert Protocol IANA has assigned a service name for the Convert Protocol from the
from the "Service Name and Transport Protocol Port Number Registry" "Service Name and Transport Protocol Port Number Registry" available
available at https://www.iana.org/assignments/service-names-port- at <https://www.iana.org/assignments/service-names-port-numbers>.
numbers/service-names-port-numbers.xhtml.
Service Name: convert Service Name: convert
Port Number: N/A Port Number: N/A
Transport Protocol(s): TCP Transport Protocol(s): TCP
Description: 0-RTT TCP Convert Protocol Description: 0-RTT TCP Convert Protocol
Assignee: IESG <iesg@ietf.org> Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org> Contact: IETF Chair <chair@ietf.org>
Reference: THISRFC Reference: RFC 8803
Clients may use this service name to fed the procedure defined in Clients may use this service name to feed the procedure defined in
[RFC2782] to discover the IP address(es) and the port number used by [RFC2782] to discover the IP address(es) and the port number used by
the Transport Converters of a domain. the Transport Converters of a domain.
10.2. The Convert Protocol (Convert) Parameters 10.2. The Convert Protocol (Convert) Parameters
IANA is requested to create a new "The TCP Convert Protocol (Convert) IANA has created a new "TCP Convert Protocol (Convert) Parameters"
Parameters" registry. registry.
The following subsections detail new registries within "The Convert The following subsections detail new registries within the "Convert
Protocol (Convert) Parameters" registry. Protocol (Convert) Parameters" registry.
The Designated Expert is expected to ascertain the existence of The designated expert is expected to ascertain the existence of
suitable documentation as described in Section 4.6 of [RFC8126] and suitable documentation as described in Section 4.6 of [RFC8126] and
to verify that the document is permanently and publicly available. to verify that the document is permanently and publicly available.
The Designated Expert is also expected to check the clarity of The designated expert is also expected to check the clarity of
purpose and use of the requested code points. purpose and use of the requested code points.
Also, criteria that should be applied by the Designated Experts Also, criteria that should be applied by the designated experts
includes determining whether the proposed registration duplicates includes determining whether the proposed registration duplicates
existing functionality, whether it is likely to be of general existing functionality, whether it is likely to be of general
applicability or whether it is useful only for a private use, and applicability or useful only for private use, and whether the
whether the registration description is clear. IANA must only accept registration description is clear. All requests should be directed
registry updates to the 128-191 range (for both "Convert TLVs" and to the review mailing list. For both the "Convert TLVs" and "Convert
"Convert Error Messages" sub-registries) from the Designated Experts Errors" subregistries, IANA must only accept registry updates in the
and should direct all requests for registration to the review mailing 128-191 range from the designated experts. It is suggested that
list. It is suggested that multiple Designated Experts be appointed. multiple designated experts be appointed. In cases where a
In cases where a registration decision could be perceived as creating registration decision could be perceived as creating a conflict of
a conflict of interest for a particular Expert, that Expert should interest for a particular expert, that expert should defer to the
defer to the judgment of the other Experts. judgment of the other experts.
10.2.1. Convert Versions 10.2.1. Convert Versions
IANA is requested to create the "Convert versions" sub-registry. New IANA has created the "Convert Versions" subregistry. New values are
values are assigned via IETF Review (Section 4.8 of [RFC8126]). assigned via IETF Review (Section 4.8 of [RFC8126]).
The initial values to be assigned at the creation of the registry are The initial values of the registry are as follows:
as follows:
+---------+--------------------------------------+-------------+ +=========+=============+===========+
| Version | Description | Reference | | Version | Description | Reference |
+---------+--------------------------------------+-------------+ +=========+=============+===========+
| 0 | Reserved | THISRFC | | 0 | Reserved | RFC 8803 |
| 1 | Assigned | THISRFC | +---------+-------------+-----------+
+---------+--------------------------------------+-------------+ | 1 | Assigned | RFC 8803 |
+---------+-------------+-----------+
Figure 27: Current Convert Versions Table 3: Current Convert Versions
10.2.2. Convert TLVs 10.2.2. Convert TLVs
IANA is requested to create the "Convert TLVs" sub-registry. The IANA has created the "Convert TLVs" subregistry. The procedures for
procedure for assigning values from this registry is as follows: assigning values from this registry are as follows:
o The values in the range 1-127 can be assigned via IETF Review. 1-127: IETF Review
o The values in the range 128-191 can be assigned via Specification 128-191: Specification Required
Required.
o The values in the range 192-255 are reserved for Private Use. 192-255: Private Use
The initial values to be assigned at the creation of the registry are The initial values of the registry are as follows:
as follows:
+---------+--------------------------------------+-------------+ +======+=============================+===========+
| Code | Name | Reference | | Code | Name | Reference |
+---------+--------------------------------------+-------------+ +======+=============================+===========+
| 0 | Reserved | THISRFC | | 0 | Reserved | RFC 8803 |
| 1 | Info TLV | THISRFC | +------+-----------------------------+-----------+
| 10 | Connect TLV | THISRFC | | 1 | Info TLV | RFC 8803 |
| 20 | Extended TCP Header TLV | THISRFC | +------+-----------------------------+-----------+
| 21 | Supported TCP Extension TLV | THISRFC | | 10 | Connect TLV | RFC 8803 |
| 22 | Cookie TLV | THISRFC | +------+-----------------------------+-----------+
| 30 | Error TLV | THISRFC | | 20 | Extended TCP Header TLV | RFC 8803 |
+---------+--------------------------------------+-------------+ +------+-----------------------------+-----------+
| 21 | Supported TCP Extension TLV | RFC 8803 |
+------+-----------------------------+-----------+
| 22 | Cookie TLV | RFC 8803 |
+------+-----------------------------+-----------+
| 30 | Error TLV | RFC 8803 |
+------+-----------------------------+-----------+
Figure 28: Initial Convert TLVs Table 4: Initial Convert TLVs
10.2.3. Convert Error Messages 10.2.3. Convert Error Messages
IANA is requested to create the "Convert Errors" sub-registry. Codes IANA has created the "Convert Errors" subregistry. Codes in this
in this registry are assigned as a function of the error type. Four registry are assigned as a function of the error type. Four types
types are defined; the following ranges are reserved for each of are defined; the following ranges are reserved for each of these
these types: types:
o Message validation and processing errors: 0-31 0-31: Message validation and processing errors
o Client-side errors: 32-63 32-63: Client-side errors
o Transport Converter-side errors: 64-95
o Errors caused by destination server: 96-127 64-95: Transport Converter-side errors
The procedure for assigning values from this sub-registry is as 96-127: Errors caused by destination Server
The procedures for assigning values from this subregistry are as
follows: follows:
o 0-127: Values in this range are assigned via IETF Review. 0-127: IETF Review
o 128-191: Values in this range are assigned via Specification 128-191: Specification Required
Required.
o 192-255: Values in this range are reserved for Private Use. 192-255: Private Use
The initial values to be assigned at the creation of the registry are The initial values of the registry are as follows:
as follows:
+-------+-----------------------------------+-----------+ +=======+=========================+===========+
| Error | Description | Reference | | Error | Description | Reference |
+-------+-----------------------------------+-----------+ +=======+=========================+===========+
| 0 | Unsupported Version | THISRFC | | 0 | Unsupported Version | RFC 8803 |
| 1 | Malformed Message | THISRFC | +-------+-------------------------+-----------+
| 2 | Unsupported Message | THISRFC | | 1 | Malformed Message | RFC 8803 |
| 3 | Missing Cookie | THISRFC | +-------+-------------------------+-----------+
| 32 | Not Authorized | THISRFC | | 2 | Unsupported Message | RFC 8803 |
| 33 | Unsupported TCP Option | THISRFC | +-------+-------------------------+-----------+
| 64 | Resource Exceeded | THISRFC | | 3 | Missing Cookie | RFC 8803 |
| 65 | Network Failure | THISRFC | +-------+-------------------------+-----------+
| 96 | Connection Reset | THISRFC | | 32 | Not Authorized | RFC 8803 |
| 97 | Destination Unreachable | THISRFC | +-------+-------------------------+-----------+
+-------+-----------------------------------+-----------+ | 33 | Unsupported TCP Option | RFC 8803 |
+-------+-------------------------+-----------+
| 64 | Resource Exceeded | RFC 8803 |
+-------+-------------------------+-----------+
| 65 | Network Failure | RFC 8803 |
+-------+-------------------------+-----------+
| 96 | Connection Reset | RFC 8803 |
+-------+-------------------------+-----------+
| 97 | Destination Unreachable | RFC 8803 |
+-------+-------------------------+-----------+
Figure 29: Initial Convert Error Codes Table 5: Initial Convert Error Codes
11. References 11. References
11.1. Normative References 11.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981, RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>. <https://www.rfc-editor.org/info/rfc793>.
[RFC2018] Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP [RFC2018] Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP
skipping to change at page 44, line 32 skipping to change at line 2092
2007, <https://www.rfc-editor.org/info/rfc4787>. 2007, <https://www.rfc-editor.org/info/rfc4787>.
[RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common [RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common
Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007, Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007,
<https://www.rfc-editor.org/info/rfc4987>. <https://www.rfc-editor.org/info/rfc4987>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925, Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>. June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<https://www.rfc-editor.org/info/rfc6824>.
[RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa, [RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
A., and H. Ashida, "Common Requirements for Carrier-Grade A., and H. Ashida, "Common Requirements for Carrier-Grade
NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888, NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
April 2013, <https://www.rfc-editor.org/info/rfc6888>. April 2013, <https://www.rfc-editor.org/info/rfc6888>.
[RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
"Special-Purpose IP Address Registries", BCP 153, "Special-Purpose IP Address Registries", BCP 153,
RFC 6890, DOI 10.17487/RFC6890, April 2013, RFC 6890, DOI 10.17487/RFC6890, April 2013,
<https://www.rfc-editor.org/info/rfc6890>. <https://www.rfc-editor.org/info/rfc6890>.
skipping to change at page 45, line 18 skipping to change at line 2120
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8684] Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
Paasch, "TCP Extensions for Multipath Operation with
Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
2020, <https://www.rfc-editor.org/info/rfc8684>.
11.2. Informative References 11.2. Informative References
[ANRW17] Trammell, B., Kuehlewind, M., De Vaere, P., Learmonth, I., [ANRW17] Trammell, B., Kuehlewind, M., De Vaere, P., Learmonth, I.,
and G. Fairhurst, "Tracking transport-layer evolution with and G. Fairhurst, "Tracking transport-layer evolution with
PATHspider", Applied Networking Research Workshop 2017 PATHspider", Applied Networking Research Workshop 2017
(ANRW17) , July 2017. (ANRW17), July 2017.
[DHC-CONVERTER]
Boucadair, M., Jacquenet, C., and T. Reddy.K, "DHCP
Options for 0-RTT TCP Converters", Work in Progress,
Internet-Draft, draft-boucadair-tcpm-dhc-converter-03, 7
October 2019, <https://tools.ietf.org/html/draft-
boucadair-tcpm-dhc-converter-03>.
[Fukuda2011] [Fukuda2011]
Fukuda, K., "An Analysis of Longitudinal TCP Passive Fukuda, K., "An Analysis of Longitudinal TCP Passive
Measurements (Short Paper)", Traffic Monitoring and Measurements (Short Paper)", Traffic Monitoring and
Analysis. TMA 2011. Lecture Notes in Computer Science, vol Analysis, TMA 2011, Lecture Notes in Computer Science,
6613. , 2011. vol. 6613, 2011.
[HotMiddlebox13b] [HOT-MIDDLEBOX13]
Detal, G., Paasch, C., and O. Bonaventure, "Multipath in Detal, G., Paasch, C., and O. Bonaventure, "Multipath in
the Middle(Box)", HotMiddlebox'13 , December 2013, the Middle(Box)", HotMiddlebox'13,
<http://inl.info.ucl.ac.be/publications/multipath- DOI 10.1145/2535828.2535829, December 2013,
<https://inl.info.ucl.ac.be/publications/multipath-
middlebox>. middlebox>.
[I-D.arkko-arch-low-latency] [IANA-CONVERT]
Arkko, J. and J. Tantsura, "Low Latency Applications and IANA, "TCP Convert Protocol (Convert) Parameters",
the Internet Architecture", draft-arkko-arch-low- <https://www.iana.org/assignments/tcp-convert-protocol-
latency-02 (work in progress), October 2017. parameters>.
[I-D.boucadair-mptcp-plain-mode]
Boucadair, M., Jacquenet, C., Bonaventure, O., Behaghel,
D., stefano.secci@lip6.fr, s., Henderickx, W., Skog, R.,
Vinapamula, S., Seo, S., Cloetens, W., Meyer, U.,
Contreras, L., and B. Peirens, "Extensions for Network-
Assisted MPTCP Deployment Models", draft-boucadair-mptcp-
plain-mode-10 (work in progress), March 2017.
[I-D.boucadair-radext-tcpm-converter] [IETFJ16] Bonaventure, O. and S. Seo, "Multipath TCP Deployments",
Boucadair, M. and C. Jacquenet, "RADIUS Extensions for IETF Journal, Vol. 12, Issue 2, November 2016.
0-RTT TCP Converters", draft-boucadair-radext-tcpm-
converter-02 (work in progress), April 2019.
[I-D.boucadair-tcpm-dhc-converter] [IMC11] Honda, K., Nishida, Y., Raiciu, C., Greenhalgh, A.,
Boucadair, M., Jacquenet, C., and T. Reddy.K, "DHCP Handley, M., and T. Hideyuki, "Is it still possible to
Options for 0-RTT TCP Converters", draft-boucadair-tcpm- extend TCP?", Proceedings of the 2011 ACM SIGCOMM
dhc-converter-03 (work in progress), October 2019. conference on Internet measurement conference,
DOI 10.1145/2068816.2068834, November 2011,
<https://doi.org/10.1145/2068816.2068834>.
[I-D.olteanu-intarea-socks-6] [INTAREA-SOCKS]
Olteanu, V. and D. Niculescu, "SOCKS Protocol Version 6", Olteanu, V. and D. Niculescu, "SOCKS Protocol Version 6",
draft-olteanu-intarea-socks-6-08 (work in progress), Work in Progress, Internet-Draft, draft-olteanu-intarea-
November 2019. socks-6-10, 13 July 2020, <https://tools.ietf.org/html/
draft-olteanu-intarea-socks-6-10>.
[I-D.peirens-mptcp-transparent] [LOW-LATENCY]
Peirens, B., Detal, G., Barre, S., and O. Bonaventure, Arkko, J. and J. Tantsura, "Low Latency Applications and
"Link bonding with transparent Multipath TCP", draft- the Internet Architecture", Work in Progress, Internet-
peirens-mptcp-transparent-00 (work in progress), July Draft, draft-arkko-arch-low-latency-02, 30 October 2017,
2016. <https://tools.ietf.org/html/draft-arkko-arch-low-latency-
02>.
[IETFJ16] Bonaventure, O. and S. Seo, "Multipath TCP Deployment", [MPTCP-PLAIN]
IETF Journal, Fall 2016 , n.d.. Boucadair, M., Jacquenet, C., Bonaventure, O., Behaghel,
D., Secci, S., Henderickx, W., Skog, R., Vinapamula, S.,
Seo, S., Cloetens, W., Meyer, U., Contreras, L., and B.
Peirens, "Extensions for Network-Assisted MPTCP Deployment
Models", Work in Progress, Internet-Draft, draft-
boucadair-mptcp-plain-mode-10, March 2017,
<https://tools.ietf.org/html/draft-boucadair-mptcp-plain-
mode-10>.
[IMC11] Honda, K., Nishida, Y., Raiciu, C., Greenhalgh, A., [MPTCP-TRANSPARENT]
Handley, M., and T. Hideyuki, "Is it still possible to Peirens, B., Detal, G., Barre, S., and O. Bonaventure,
extend TCP?", Proceedings of the 2011 ACM SIGCOMM "Link bonding with transparent Multipath TCP", Work in
conference on Internet measurement conference , 2011. Progress, Internet-Draft, draft-peirens-mptcp-transparent-
00, 8 July 2016, <https://tools.ietf.org/html/draft-
peirens-mptcp-transparent-00>.
[RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers",
RFC 1812, DOI 10.17487/RFC1812, June 1995, RFC 1812, DOI 10.17487/RFC1812, June 1995,
<https://www.rfc-editor.org/info/rfc1812>. <https://www.rfc-editor.org/info/rfc1812>.
[RFC1919] Chatel, M., "Classical versus Transparent IP Proxies", [RFC1919] Chatel, M., "Classical versus Transparent IP Proxies",
RFC 1919, DOI 10.17487/RFC1919, March 1996, RFC 1919, DOI 10.17487/RFC1919, March 1996,
<https://www.rfc-editor.org/info/rfc1919>. <https://www.rfc-editor.org/info/rfc1919>.
[RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and [RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
skipping to change at page 48, line 30 skipping to change at line 2289
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[RFC8548] Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack, [RFC8548] Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack,
Q., and E. Smith, "Cryptographic Protection of TCP Streams Q., and E. Smith, "Cryptographic Protection of TCP Streams
(tcpcrypt)", RFC 8548, DOI 10.17487/RFC8548, May 2019, (tcpcrypt)", RFC 8548, DOI 10.17487/RFC8548, May 2019,
<https://www.rfc-editor.org/info/rfc8548>. <https://www.rfc-editor.org/info/rfc8548>.
[TS23501] 3GPP (3rd Generation Partnership Project), ., "Technical [TCPM-CONVERTER]
Boucadair, M. and C. Jacquenet, "RADIUS Extensions for
0-RTT TCP Converters", Work in Progress, Internet-Draft,
draft-boucadair-opsawg-tcpm-converter-01, 28 February
2020, <https://tools.ietf.org/html/draft-boucadair-opsawg-
tcpm-converter-01>.
[TS23501] 3GPP (3rd Generation Partnership Project), "Technical
Specification Group Services and System Aspects; System Specification Group Services and System Aspects; System
Architecture for the 5G System; Stage 2 (Release 16)", architecture for the 5G System; Stage 2 (Release 16)",
2019, <https://www.3gpp.org/ftp/Specs/ 2019, <https://www.3gpp.org/ftp/Specs/
archive/23_series/23.501/>. archive/23_series/23.501/>.
Appendix A. Example Socket API Changes to Support the 0-RTT Convert Appendix A. Example Socket API Changes to Support the 0-RTT TCP Convert
Protocol Protocol
A.1. Active Open (Client Side) A.1. Active Open (Client Side)
On the client side, the support of the 0-RTT Converter protocol does On the Client side, the support of the 0-RTT Converter protocol does
not require any other changes than those identified in Appendix A of not require any other changes than those identified in Appendix A of
[RFC7413]. Those modifications are already supported by multiple TCP [RFC7413]. Those modifications are already supported by multiple TCP
stacks. stacks.
As an example, on Linux, a client can send the 0-RTT Convert message As an example, on Linux, a Client can send the 0-RTT Convert message
inside a SYN by using sendto with the MSG_FASTOPEN flag as shown in inside a SYN by using sendto with the MSG_FASTOPEN flag as shown in
the example below: the example below:
s = socket(AF_INET, SOCK_STREAM, 0); s = socket(AF_INET, SOCK_STREAM, 0);
sendto(s, buffer, buffer_len, MSG_FASTOPEN, sendto(s, buffer, buffer_len, MSG_FASTOPEN,
(struct sockaddr *) &server_addr, addr_len); (struct sockaddr *) &server_addr, addr_len);
The client side of the Linux TCP TFO can be used in two different The Client side of the Linux TFO can be used in two different modes
modes depending on the host configuration (sysctl tcp_fastopen depending on the host configuration (sysctl tcp_fastopen variable):
variable):
o 0x1: (client) enables sending data in the opening SYN on the 0x1: (client) enables sending data in the opening SYN on the Client.
client.
o 0x4: (client) send data in the opening SYN regardless of cookie 0x4: (client) enables sending data in the opening SYN regardless of
availability and without a cookie option. cookie availability and without a cookie option.
By setting this configuration variable to 0x5, a Linux client using By setting this configuration variable to 0x5, a Linux Client using
the above code would send data inside the SYN without using a TFO the above code would send data inside the SYN without using a TFO
option. option.
A.2. Passive Open (Converter Side) A.2. Passive Open (Converter Side)
The Converter needs to enable the reception of data inside the SYN The Converter needs to enable the reception of data inside the SYN
independently of the utilization of the TFO option. This implies independently of the utilization of the TFO option. This implies
that the Transport Converter application cannot rely on the TFO that the Transport Converter application cannot rely on the Fast Open
cookies to validate the reachability of the IP address that sent the Cookies to validate the reachability of the IP address that sent the
SYN. It must rely on other techniques, such as the Cookie TLV SYN. It must rely on other techniques, such as the Cookie TLV
described in this document, to verify this reachability. described in this document, to verify this reachability.
[RFC7413] suggested the utilization of a TCP_FASTOPEN socket option [RFC7413] suggested the utilization of a TCP_FASTOPEN socket option
the enable the reception of SYNs containing data. Later, Appendix A to enable the reception of SYNs containing data. Later, Appendix A
of [RFC7413], mentioned: of [RFC7413] mentioned:
Traditionally, accept() returns only after a socket is connected. | Traditionally, accept() returns only after a socket is connected.
But, for a Fast Open connection, accept() returns upon receiving | But, for a Fast Open connection, accept() returns upon receiving a
SYN with a valid Fast Open cookie and data, and the data is available | SYN with a valid Fast Open cookie and data, and the data is
to be read through, e.g., recvmsg(), read(). | available to be read through, e.g., recvmsg(), read().
To support the 0-RTT Convert Protocol, this behavior should be To support the 0-RTT TCP Convert Protocol, this behavior should be
modified as follows: modified as follows:
Traditionally, accept() returns only after a socket is connected. | Traditionally, accept() returns only after a socket is connected.
But, for a Fast Open connection, accept() returns upon receiving a | But, for a Fast Open connection, accept() returns upon receiving a
SYN with data, and the data is available to be read through, e.g., | SYN with data, and the data is available to be read through, e.g.,
recvmsg(), read(). The application that receives such SYNs with data | recvmsg(), read(). The application that receives such SYNs with
must be able to validate the reachability of the source of the SYN | data must be able to validate the reachability of the source of
and also deal with replayed SYNs. | the SYN and also deal with replayed SYNs.
The Linux server side can be configured with the following sysctls: The Linux Server side can be configured with the following sysctls:
o 0x2: (server) enables the server support, i.e., allowing data in a 0x2: (server) enables the Server support, i.e., allowing data in a
SYN packet to be accepted and passed to the application before SYN packet to be accepted and passed to the application before a
3-way handshake finishes. 3-way handshake finishes.
o 0x200: (server) accept data-in-SYN w/o any cookie option present. 0x200: (server) accepts data-in-SYN w/o any cookie option present.
However, this configuration is system-wide. This is convenient for However, this configuration is system wide. This is convenient for
typical Transport Converter deployments where no other applications typical Transport Converter deployments where no other applications
relying on TFO are collocated on the same device. relying on TFO are collocated on the same device.
Recently, the TCP_FASTOPEN_NO_COOKIE socket option has been added to Recently, the TCP_FASTOPEN_NO_COOKIE socket option has been added to
provide the same behavior on a per socket basis. This enables a provide the same behavior on a per-socket basis. This enables a
single host to support both servers that require the TFO cookie and single host to support both Servers that require the Fast Open Cookie
servers that do not use it. and Servers that do not use it.
Acknowledgments Acknowledgments
Although they could disagree with the contents of the document, we Although they could disagree with the contents of the document, we
would like to thank Joe Touch and Juliusz Chroboczek whose comments would like to thank Joe Touch and Juliusz Chroboczek, whose comments
on the MPTCP mailing list have forced us to reconsider the design of on the MPTCP mailing list have forced us to reconsider the design of
the solution several times. the solution several times.
We would like to thank Raphael Bauduin, Stefano Secci, Anandatirtha We would like to thank Raphael Bauduin, Stefano Secci, Anandatirtha
Nandugudi and Gregory Vander Schueren for their help in preparing Nandugudi, and Gregory Vander Schueren for their help in preparing
this document. Nandini Ganesh provided valuable feedback about the this document. Nandini Ganesh provided valuable feedback about the
handling of TFO and the error codes. Yuchung Cheng and Praveen handling of TFO and the error codes. Yuchung Cheng and Praveen
Balasubramanian helped to clarify the discussion on supplying data in Balasubramanian helped to clarify the discussion on supplying data in
SYNs. Phil Eardley and Michael Scharf's helped to clarify different SYNs. Phil Eardley and Michael Scharf helped to clarify different
parts of the text. Thanks to Eric Vyncke, Roman Danyliw, Benjamin parts of the text. Thanks to Éric Vyncke, Roman Danyliw, Benjamin
Kaduk, and Alexey Melnikov for the IESG review, and Christian Huitema Kaduk, and Alexey Melnikov for the IESG review, and Christian Huitema
for the security directorate review. for the Security Directorate review.
Many thanks to Mirja Kuehlewind for the detailed AD review. Many thanks to Mirja Kühlewind for the detailed AD review.
This document builds upon earlier documents that proposed various This document builds upon earlier documents that proposed various
forms of Multipath TCP proxies [I-D.boucadair-mptcp-plain-mode], forms of Multipath TCP proxies: [MPTCP-PLAIN], [MPTCP-TRANSPARENT],
[I-D.peirens-mptcp-transparent] and [HotMiddlebox13b]. and [HOT-MIDDLEBOX13].
From [I-D.boucadair-mptcp-plain-mode]: From [MPTCP-PLAIN]:
Many thanks to Chi Dung Phung, Mingui Zhang, Rao Shoaib, Yoshifumi Many thanks to Chi Dung Phung, Mingui Zhang, Rao Shoaib, Yoshifumi
Nishida, and Christoph Paasch for their valuable comments. Nishida, and Christoph Paasch for their valuable comments.
Thanks to Ian Farrer, Mikael Abrahamsson, Alan Ford, Dan Wing, and Thanks to Ian Farrer, Mikael Abrahamsson, Alan Ford, Dan Wing, and
Sri Gundavelli for the fruitful discussions in IETF#95 (Buenos Sri Gundavelli for the fruitful discussions at IETF 95 (Buenos
Aires). Aires).
Special thanks to Pierrick Seite, Yannick Le Goff, Fred Klamm, and Special thanks to Pierrick Seite, Yannick Le Goff, Fred Klamm, and
Xavier Grall for their inputs. Xavier Grall for their input.
Thanks also to Olaf Schleusing, Martin Gysi, Thomas Zasowski, Andreas Thanks also to Olaf Schleusing, Martin Gysi, Thomas Zasowski, Andreas
Burkhard, Silka Simmen, Sandro Berger, Michael Melloul, Jean-Yves Burkhard, Silka Simmen, Sandro Berger, Michael Melloul, Jean-Yves
Flahaut, Adrien Desportes, Gregory Detal, Benjamin David, Arun Flahaut, Adrien Desportes, Gregory Detal, Benjamin David, Arun
Srinivasan, and Raghavendra Mallya for the discussion. Srinivasan, and Raghavendra Mallya for their input.
Contributors Contributors
Bart Peirens contributed to an early version of the document. Bart Peirens contributed to an early draft version of this document.
As noted above, this document builds on two previous documents. As noted above, this document builds on two previous documents.
The authors of [I-D.boucadair-mptcp-plain-mode] were: The authors of [MPTCP-PLAIN] were:
o Mohamed Boucadair * Mohamed Boucadair
o Christian Jacquenet * Christian Jacquenet
o Olivier Bonaventure * Olivier Bonaventure
o Denis Behaghel * Denis Behaghel
o Stefano Secci * Stefano Secci
o Wim Henderickx * Wim Henderickx
o Robert Skog * Robert Skog
o Suresh Vinapamula * Suresh Vinapamula
o SungHoon Seo * SungHoon Seo
o Wouter Cloetens * Wouter Cloetens
o Ullrich Meyer * Ullrich Meyer
o Luis M. Contreras * Luis M. Contreras
o Bart Peirens * Bart Peirens
The authors of [I-D.peirens-mptcp-transparent] were: The authors of [MPTCP-TRANSPARENT] were:
o Bart Peirens * Bart Peirens
o Gregory Detal * Gregory Detal
o Sebastien Barre
o Olivier Bonaventure * Sebastien Barre
* Olivier Bonaventure
Authors' Addresses Authors' Addresses
Olivier Bonaventure (editor) Olivier Bonaventure (editor)
Tessares Tessares
Avenue Jean Monnet 1
B-1348 Louvain-la-Neuve
Belgium
Email: Olivier.Bonaventure@tessares.net Email: Olivier.Bonaventure@tessares.net
Mohamed Boucadair (editor) Mohamed Boucadair (editor)
Orange Orange
Clos Courtel Clos Courtel
Rennes 35000 35000 Rennes
France France
Email: mohamed.boucadair@orange.com Email: mohamed.boucadair@orange.com
Sri Gundavelli Sri Gundavelli
Cisco Cisco
170 West Tasman Drive
San Jose, CA 95134
United States of America
Email: sgundave@cisco.com Email: sgundave@cisco.com
SungHoon Seo SungHoon Seo
Korea Telecom Korea Telecom
151 Taebong-ro
Seocho-gu, Seoul, 06763
Republic of Korea
Email: sh.seo@kt.com Email: sh.seo@kt.com
Benjamin Hesmans Benjamin Hesmans
Tessares Tessares
Avenue Jean Monnet 1
B-1348 Louvain-la-Neuve
Belgium
Email: Benjamin.Hesmans@tessares.net Email: Benjamin.Hesmans@tessares.net
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