--- 1/draft-ietf-dtn-tcpclv4-05.txt 2018-01-28 20:13:09.058028061 -0800 +++ 2/draft-ietf-dtn-tcpclv4-06.txt 2018-01-28 20:13:09.138029964 -0800 @@ -1,22 +1,22 @@ Delay Tolerant Networking B. Sipos Internet-Draft RKF Engineering Obsoletes: 7242 (if approved) M. Demmer Intended status: Standards Track UC Berkeley -Expires: June 17, 2018 J. Ott +Expires: August 1, 2018 J. Ott Aalto University S. Perreault - December 14, 2017 + January 28, 2018 Delay-Tolerant Networking TCP Convergence Layer Protocol Version 4 - draft-ietf-dtn-tcpclv4-05 + draft-ietf-dtn-tcpclv4-06 Abstract This document describes a revised protocol for the TCP-based convergence layer (TCPCL) for Delay-Tolerant Networking (DTN). The protocol revision is based on implementation issues in the original TCPCL Version 3 and updates to the Bundle Protocol contents, encodings, and convergence layer requirements in Bundle Protocol Version 7. Specifically, the TCPCLv4 uses CBOR-encoded BPv7 bundles as its service data unit being transported and provides a reliable @@ -32,105 +32,109 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on June 17, 2018. + This Internet-Draft will expire on August 1, 2018. Copyright Notice - Copyright (c) 2017 IETF Trust and the persons identified as the + Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 - 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 - 2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 4 - 3. General Protocol Description . . . . . . . . . . . . . . . . 6 - 3.1. TCPCL Session Overview . . . . . . . . . . . . . . . . . 6 - 3.2. Example Message Exchange . . . . . . . . . . . . . . . . 7 + 1.1. Convergence Layer Services . . . . . . . . . . . . . . . 4 + 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 6 + 2.1. Definitions Specific to the TCPCL Protocol . . . . . . . 6 + 3. General Protocol Description . . . . . . . . . . . . . . . . 7 + 3.1. TCPCL Session Overview . . . . . . . . . . . . . . . . . 7 + 3.2. Example Message Exchange . . . . . . . . . . . . . . . . 8 4. Session Establishment . . . . . . . . . . . . . . . . . . . . 9 - 4.1. Contact Header . . . . . . . . . . . . . . . . . . . . . 10 - 4.1.1. Header Extension Items . . . . . . . . . . . . . . . 12 - 4.2. Validation and Parameter Negotiation . . . . . . . . . . 13 - 4.3. Session Security . . . . . . . . . . . . . . . . . . . . 15 - 4.3.1. TLS Handshake Result . . . . . . . . . . . . . . . . 15 - 4.3.2. Example TLS Initiation . . . . . . . . . . . . . . . 15 - 5. Established Session Operation . . . . . . . . . . . . . . . . 16 - 5.1. Message Type Codes . . . . . . . . . . . . . . . . . . . 16 - 5.2. Upkeep and Status Messages . . . . . . . . . . . . . . . 17 - 5.2.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 17 - 5.2.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 18 - 5.3. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 19 - 5.3.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 19 - 5.3.2. Transfer Initialization (XFER_INIT) . . . . . . . . . 20 - 5.3.3. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 21 - 5.3.4. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 22 - 5.3.5. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 23 - 6. Session Termination . . . . . . . . . . . . . . . . . . . . . 25 - 6.1. Shutdown Message (SHUTDOWN) . . . . . . . . . . . . . . . 25 - 6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 28 - 7. Security Considerations . . . . . . . . . . . . . . . . . . . 28 - 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 - 8.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 30 - 8.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 30 - 8.3. Header Extension Types . . . . . . . . . . . . . . . . . 31 - 8.4. Message Types . . . . . . . . . . . . . . . . . . . . . . 31 - 8.5. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 32 - 8.6. SHUTDOWN Reason Codes . . . . . . . . . . . . . . . . . . 33 - 8.7. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 34 - - 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 34 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 34 - 10.1. Normative References . . . . . . . . . . . . . . . . . . 34 - 10.2. Informative References . . . . . . . . . . . . . . . . . 35 - Appendix A. Significant changes from RFC7242 . . . . . . . . . . 36 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37 + 4.1. TCP Connection . . . . . . . . . . . . . . . . . . . . . 10 + 4.2. Contact Header . . . . . . . . . . . . . . . . . . . . . 10 + 4.2.1. Header Extension Items . . . . . . . . . . . . . . . 13 + 4.3. Validation and Parameter Negotiation . . . . . . . . . . 14 + 4.4. Session Security . . . . . . . . . . . . . . . . . . . . 15 + 4.4.1. TLS Handshake Result . . . . . . . . . . . . . . . . 16 + 4.4.2. Example TLS Initiation . . . . . . . . . . . . . . . 16 + 5. Established Session Operation . . . . . . . . . . . . . . . . 17 + 5.1. Message Type Codes . . . . . . . . . . . . . . . . . . . 17 + 5.2. Upkeep and Status Messages . . . . . . . . . . . . . . . 18 + 5.2.1. Session Upkeep (KEEPALIVE) . . . . . . . . . . . . . 18 + 5.2.2. Message Rejection (MSG_REJECT) . . . . . . . . . . . 19 + 5.3. Bundle Transfer . . . . . . . . . . . . . . . . . . . . . 20 + 5.3.1. Bundle Transfer ID . . . . . . . . . . . . . . . . . 21 + 5.3.2. Transfer Initialization (XFER_INIT) . . . . . . . . . 21 + 5.3.3. Data Transmission (XFER_SEGMENT) . . . . . . . . . . 22 + 5.3.4. Data Acknowledgments (XFER_ACK) . . . . . . . . . . . 24 + 5.3.5. Transfer Refusal (XFER_REFUSE) . . . . . . . . . . . 25 + 6. Session Termination . . . . . . . . . . . . . . . . . . . . . 27 + 6.1. Shutdown Message (SHUTDOWN) . . . . . . . . . . . . . . . 27 + 6.2. Idle Session Shutdown . . . . . . . . . . . . . . . . . . 29 + 7. Security Considerations . . . . . . . . . . . . . . . . . . . 29 + 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 + 8.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 31 + 8.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 31 + 8.3. Header Extension Types . . . . . . . . . . . . . . . . . 32 + 8.4. Message Types . . . . . . . . . . . . . . . . . . . . . . 33 + 8.5. XFER_REFUSE Reason Codes . . . . . . . . . . . . . . . . 33 + 8.6. SHUTDOWN Reason Codes . . . . . . . . . . . . . . . . . . 34 + 8.7. MSG_REJECT Reason Codes . . . . . . . . . . . . . . . . . 35 + 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 35 + 10.1. Normative References . . . . . . . . . . . . . . . . . . 35 + 10.2. Informative References . . . . . . . . . . . . . . . . . 36 + Appendix A. Significant changes from RFC7242 . . . . . . . . . . 37 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38 1. Introduction This document describes the TCP-based convergence-layer protocol for Delay-Tolerant Networking. Delay-Tolerant Networking is an end-to- end architecture providing communications in and/or through highly stressed environments, including those with intermittent connectivity, long and/or variable delays, and high bit error rates. More detailed descriptions of the rationale and capabilities of these networks can be found in "Delay-Tolerant Network Architecture" [RFC4838]. An important goal of the DTN architecture is to accommodate a wide range of networking technologies and environments. The protocol used - for DTN communications is the revised Bundle Protocol (BP) + for DTN communications is the Bundle Protocol Version 7 (BPv7) [I-D.ietf-dtn-bpbis], an application-layer protocol that is used to - construct a store-and- forward overlay network. As described in the - Bundle Protocol specification [I-D.ietf-dtn-bpbis], it requires the + construct a store-and-forward overlay network. BPv7 requires the services of a "convergence- layer adapter" (CLA) to send and receive bundles using the service of some "native" link, network, or Internet protocol. This document describes one such convergence-layer adapter that uses the well-known Transmission Control Protocol (TCP). This - convergence layer is referred to as TCPCL. + convergence layer is referred to as TCP Convergence Layer Version 4 + (TCPCLv4). For the remainder of this document, the abbreviation "BP" + without the version suffix refers to BPv7. For the remainder of this + document, the abbreviation "TCPCL" without the version suffix refers + to TCPCLv4. The locations of the TCPCL and the BP in the Internet model protocol stack (described in [RFC1122]) are shown in Figure 1. In particular, when BP is using TCP as its bearer with TCPCL as its convergence layer, both BP and TCPCL reside at the application layer of the Internet model. +-------------------------+ | DTN Application | -\ +-------------------------| | @@ -155,80 +159,137 @@ document does not address: o The format of protocol data units of the Bundle Protocol, as those are defined elsewhere in [RFC5050] and [I-D.ietf-dtn-bpbis]. This includes the concept of bundle fragmentation or bundle encapsulation. The TCPCL transfers bundles as opaque data blocks. o Mechanisms for locating or identifying other bundle nodes within an internet. +1.1. Convergence Layer Services + + This version of the TCPCL provides the following services to support + the overlaying Bundle Protocol agent: + + Attempt Session The TCPCL allows a BP agent to pre-emptively attempt + to establish a TCPCL session with a peer node. Each session + attempt can send a different set of contact header parameters as + directed by the BP agent. + + Session Started The TCPCL supports indication when a new TCP + connection has been started (as either client or server) before + the TCPCL handshake has begun. + + Session Established The TCPCL supports indication when a new session + has been fully established and is ready for its first transfer. + + Session Shutdown The TCPCL supports indication when an established + session has been ended by normal exchange of SHUTDOWN messages + with all transfers completed. + + Session Failed The TCPCL supports indication when a session fails, + either during contact negotiation, TLS negotiation, or after + establishement for any reason other than normal shutdown. + + Transmission Availability Because TCPCL transmits serially over a + TCP connection, it suffers from "head of queue blocking" and + supports indication of when an established session is live-but- + idle (i.e. available for immediate transfer start) or live-and- + not-idle. + + Transmission Success The TCPCL supports positive indication when a + bundle has been fully transferred to a peer node. + + Transmission Intermediate Progress The TCPCL supports positive + indication of intermediate progress of transferr to a peer node. + This intermediate progress is at the granularity of each + transferred segment. + + Transmission Failure The TCPCL supports positive indication of + certain reasons for bundle transmission failure, notably when the + peer node rejects the bundle or when a TCPCL session ends before + transferr success. The TCPCL itself does not have a notion of + transfer timeout. + + Reception Interruption The TCPCL allows a BP agent to interrupt an + individual transfer before it has fully completed (successfully or + not). + + Reception Success The TCPCL supports positive indication when a + bundle has been fully transferred from a peer node. + + Reception Intermediate Progress The TCPCL supports positive + indication of intermediate progress of transfer from the peer + node. This intermediate progress is at the granularity of each + transferred segment. Intermediate reception indication allows a + BP agent the chance to inspect bundle header contents before the + entire bundle is available, and thus supports the "Reception + Interruption" capability. + + Reception Failure The TCPCL supports positive indication of certain + reasons for reception failure, notably when the local node rejects + an attempted transfer for some local policy reason or when a TCPCL + session ends before transfer success. The TCPCL itself does not + have a notion of transfer timeout. + 2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2.1. Definitions Specific to the TCPCL Protocol - This section contains definitions that are interpreted to be specific - to the operation of the TCPCL protocol, as described below. + This section contains definitions specific to the TCPCL protocol. - TCPCL Node: A TCPCL node refers to either side of an negotiating or - in-service TCPCL Session. For most TCPCL behavior, the two nodes - are symmetric and there is no protocol distinction between them. - Some specific behavior, particularly during negotiation, - distinguishes between the connecting node and the connected-to - node. For the remainder of this document, the term "node" without - the prefix "TCPCL" refers to a TCPCL node. + TCPCL Node: This term refers to either side of a negotiating or in- + service TCPCL Session. For most TCPCL behavior, the two nodes are + symmetric and there is no protocol distinction between them. Some + specific behavior, particularly during negotiation, distinguishes + between the connecting node and the connected-to node. For the + remainder of this document, the term "node" without the prefix + "TCPCL" refers to a TCPCL node. - TCP Connection: A TCP connection refers to a transport connection - using TCP as the transport protocol. + TCP Connection: This term refers to a transport connection using TCP + as the transport protocol. TCPCL Session: A TCPCL session (as opposed to a TCP connection) is a TCPCL communication relationship between two bundle nodes. The lifetime of a TCPCL session is bound to the lifetime of an - underlying TCP connection. Therefore, a TCPCL session is - initiated after a bundle node establishes a TCP connection to for - the purposes of bundle communication. A TCPCL session is - terminated when the TCP connection ends, due either to one or both - nodes actively terminating the TCP connection or due to network - errors causing a failure of the TCP connection. For the remainder - of this document, the term "session" without the prefix "TCPCL" - refers to a TCPCL session. + underlying TCP connection. A TCPCL session is terminated when the + TCP connection ends, due either to one or both nodes actively + terminating the TCP connection or due to network errors causing a + failure of the TCP connection. For the remainder of this + document, the term "session" without the prefix "TCPCL" refers to + a TCPCL session. - Session parameters: The session parameters are a set of values used - to affect the operation of the TCPCL for a given session. The - manner in which these parameters are conveyed to the bundle node - and thereby to the TCPCL is implementation dependent. However, - the mechanism by which two bundle nodes exchange and negotiate the - values to be used for a given session is described in Section 4.2. + Session parameters: These are a set of values used to affect the + operation of the TCPCL for a given session. The manner in which + these parameters are conveyed to the bundle node and thereby to + the TCPCL is implementation dependent. However, the mechanism by + which two bundle nodes exchange and negotiate the values to be + used for a given session is described in Section 4.3. - Transfer: Transfer refers to the procedures and mechanisms - (described below) for conveyance of an individual bundle from one - node to another. Each transfer within TCPCLv4 is identified by a - Transfer ID number which is unique only to a single direction - within a single Session. + Transfer: This refers to the procedures and mechanisms for + conveyance of an individual bundle from one node to another. Each + transfer within TCPCL is identified by a Transfer ID number which + is unique only to a single direction within a single Session. Idle Session: A TCPCL session is idle while the only messages being transmitted or received are KEEPALIVE messages. - Lively Session: A TCPCL session is lively while any messages are - being transmitted or received. + Live Session: A TCPCL session is live while any messages are being + transmitted or received. Reason Codes: The TCPCL uses numeric codes to encode specific - reasons for individual failure/error message types. This limits - the expressiveness of TCPCL error encodings, but simplifies the - encoding of errors and allows an application policy to attempt - recovery from expected 'failure' modes (e.g. if a Session cannot - be established with USE_TLS disabled because of a Contact Failure - shutdown, a re-attempt can be made with USE_TLS enabled). + reasons for individual failure/error message types. 3. General Protocol Description The service of this protocol is the transmission of DTN bundles via the Transmission Control Protocol (TCP). This document specifies the encapsulation of bundles, procedures for TCP setup and teardown, and a set of messages and node requirements. The general operation of the protocol is as follows. 3.1. TCPCL Session Overview @@ -239,73 +300,58 @@ exchanged in both directions to set parameters of the TCPCL session and exchange a singleton endpoint identifier for each node (not the singleton Endpoint Identifier (EID) of any application running on the node) to denote the bundle-layer identity of each DTN node. This is used to assist in routing and forwarding messages (e.g. to prevent loops). Once the TCPCL session is established and configured in this way, bundles can be transferred in either direction. Each transfer is performed by an initialization (XFER_INIT) message followed by one or - more logical segments of data within an XFER_SEGMENT message. The - choice of the length to use for segments is an implementation matter, - but each segment must be no larger than the receiving node's maximum - receive unit (MRU) (see the field "Segment MRU" of Section 4.1). The - first segment for a bundle MUST set the 'START' flag, and the last - one MUST set the 'end' flag in the XFER_SEGMENT message flags. - - If multiple bundles are transmitted on a single TCPCL connection, - they MUST be transmitted consecutively. Interleaving data segments - from different bundles is not allowed. Bundle interleaving can be - accomplished by fragmentation at the BP layer or by establishing - multiple TCPCL sessions. + more logical segments of data within an XFER_SEGMENT message. + Multiple bundles can be transmitted consecutively on a single TCPCL + connection. Segments from different bundles are never interleaved. + Bundle interleaving can be accomplished by fragmentation at the BP + layer or by establishing multiple TCPCL sessions between the same + peers. A feature of this protocol is for the receiving node to send - acknowledgments as bundle data segments arrive (XFER_ACK). The - rationale behind these acknowledgments is to enable the sender node - to determine how much of the bundle has been received, so that in - case the session is interrupted, it can perform reactive + acknowledgment (XFER_ACK) messages as bundle data segments arrive . + The rationale behind these acknowledgments is to enable the sender + node to determine how much of the bundle has been received, so that + in case the session is interrupted, it can perform reactive fragmentation to avoid re-sending the already transmitted part of the - bundle. For each data segment that is received, the receiving node - sends an XFER_ACK message containing the cumulative length of the - bundle that has been received. The sending node MAY transmit - multiple XFER_SEGMENT messages without necessarily waiting for the - corresponding XFER_ACK responses. This enables pipelining of - messages on a channel. In addition, there is no explicit flow - control on the TCPCL layer. + bundle. In addition, there is no explicit flow control on the TCPCL + layer. - Another feature is that a receiver MAY interrupt the transmission of - a bundle at any point in time by replying with a XFER_REFUSE message, - which causes the sender to stop transmission of the current bundle, - after completing transmission of a partially sent data segment. - Note: This enables a cross-layer optimization in that it allows a - receiver that detects that it already has received a certain bundle - to interrupt transmission as early as possible and thus save - transmission capacity for other bundles. + A TCPCL receiver can interrupt the transmission of a bundle at any + point in time by replying with a XFER_REFUSE message, which causes + the sender to stop transmission of the associated bundle (if it + hasn't already finished transmission) Note: This enables a cross- + layer optimization in that it allows a receiver that detects that it + already has received a certain bundle to interrupt transmission as + early as possible and thus save transmission capacity for other + bundles. For sessions that are idle, a KEEPALIVE message is sent at a - negotiated interval. This is used to convey node liveliqness + negotiated interval. This is used to convey node live-ness information during otherwise message-less time intervals. - Finally, before sessions close, a SHUTDOWN message is sent to the - session peer (see Section 6.1). After sending a SHUTDOWN message, - the peer can not initiate any further transfers and the session - enters a closing-down phase. After receiving a SHUTDOWN message and - when no transfers are in-progress (i.e. have pending or - unacknowledged segments), the receiving peer can close the session - without chance of lost transfers. A SHUTDOWN message can also be - used to refuse a session setup by a peer (see Section 4.2). It is an - implementation matter to determine whether or not to close a TCPCL - session while there are no transfers queued or in-progress. + A SHUTDOWN message is used to start the closing of a TCPCL session + (see Section 6.1). During shutdown sequencing, in-progress transfers + can be completed but no new transfers can be initiated. A SHUTDOWN + message can also be used to refuse a session setup by a peer (see + Section 4.3). It is an implementation matter to determine whether or + not to close a TCPCL session while there are no transfers queued or + in-progress. - There are specific messages for sending and receiving operations (in - addition to session setup/teardown). TCPCL is symmetric, i.e., both + TCPCL is a symmetric protocol between the peers of a session. Both sides can start sending data segments in a session, and one side's bundle transfer does not have to complete before the other side can start sending data segments on its own. Hence, the protocol allows for a bi-directional mode of communication. Note that in the case of concurrent bidirectional transmission, acknowledgment segments MAY be interleaved with data segments. 3.2. Example Message Exchange The following figure depicts the protocol exchange for a simple @@ -365,72 +411,69 @@ +-------------------------+ +-------------------------+ Figure 2: An Example of the Flow of Protocol Messages on a Single TCP Session between Two Nodes (A and B) 4. Session Establishment For bundle transmissions to occur using the TCPCL, a TCPCL session MUST first be established between communicating nodes. It is up to the implementation to decide how and when session setup is triggered. + For example, some sessions MAY be opened proactively and maintained for as long as is possible given the network conditions, while other sessions MAY be opened only when there is a bundle that is queued for transmission and the routing algorithm selects a certain next-hop node. +4.1. TCP Connection + To establish a TCPCL session, a node MUST first establish a TCP connection with the intended peer node, typically by using the services provided by the operating system. Destination port number 4556 has been assigned by IANA as the Registered Port number for the TCP convergence layer. Other destination port numbers MAY be used per local configuration. Determining a peer's destination port number (if different from the registered TCPCL port number) is up to the implementation. Any source port number MAY be used for TCPCL sessions. Typically an operating system assigned number in the TCP - Ephemeral range (49152--65535) is used. + Ephemeral range (49152-65535) is used. If the node is unable to establish a TCP connection for any reason, then it is an implementation matter to determine how to handle the connection failure. A node MAY decide to re-attempt to establish the connection. If it does so, it MUST NOT overwhelm its target with repeated connection attempts. Therefore, the node MUST retry the - connection setup only after some delay (a 1-second minimum is - RECOMMENDED), and it SHOULD use a (binary) exponential backoff - mechanism to increase this delay in case of repeated failures. In - case a SHUTDOWN message specifying a reconnection delay is received, - that delay is used as the initial delay. The default initial delay - SHOULD be at least 1 second but SHOULD be configurable since it will - be application and network type dependent. - - The node MAY declare failure after one or more connection attempts - and MAY attempt to find an alternate route for bundle data. Such - decisions are up to the higher layer (i.e., the BP). + connection setup no earlier than some delay time from the last + attempt, and it SHOULD use a (binary) exponential backoff mechanism + to increase this delay in case of repeated failures. In case a + SHUTDOWN message specifying a reconnection delay is received, that + delay is used as the initial delay. The default initial re-attempt + delay SHOULD be no shorter than 1 second and SHOULD be configurable + since it will be application and network type dependent. Once a TCP connection is established, each node MUST immediately transmit a contact header over the TCP connection. The format of the - contact header is described in Section 4.1. - - Upon receipt of the contact header, both nodes perform the validation - and negotiation procedures defined in Section 4.2 - - After receiving the contact header from the other node, either node - MAY also refuse the session by sending a SHUTDOWN message. If - session setup is refused, a reason MUST be included in the SHUTDOWN - message. + contact header is described in Section 4.2. -4.1. Contact Header +4.2. Contact Header Once a TCP connection is established, both parties exchange a contact header. This section describes the format of the contact header and the meaning of its fields. + Upon receipt of the contact header, both nodes perform the validation + and negotiation procedures defined in Section 4.3. After receiving + the contact header from the other node, either node MAY refuse the + session by sending a SHUTDOWN message with an appropriate reason + code. + The format for the Contact Header is as follows: 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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 +---------------+---------------+---------------+---------------+ | magic='dtn!' | +---------------+---------------+---------------+---------------+ | Version | Flags | Keepalive Interval | +---------------+---------------+---------------+---------------+ | Segment MRU... | @@ -447,21 +490,21 @@ +---------------+---------------+---------------+---------------+ | Header Extension Length... | +---------------+---------------+---------------+---------------+ | contd. | +---------------+---------------+---------------+---------------+ | Header Extension Items... | +---------------+---------------+---------------+---------------+ Figure 3: Contact Header Format - See Section 4.2 for details on the use of each of these contact + See Section 4.3 for details on the use of each of these contact header fields. The fields of the contact header are: magic: A four-octet field that always contains the octet sequence 0x64 0x74 0x6e 0x21, i.e., the text string "dtn!" in US-ASCII (and UTF-8). Version: A one-octet field value containing the value 4 (current version of the protocol). Flags: A one-octet field of single-bit flags, interpreted according @@ -476,109 +519,109 @@ Segment MRU: A 64-bit unsigned integer indicating the largest allowable single-segment data payload size to be received in this session. Any XFER_SEGMENT sent to this peer SHALL have a data payload no longer than the peer's Segment MRU. The two nodes of a single session MAY have different Segment MRUs, and no relation between the two is required. Transfer MRU: A 64-bit unsigned integer indicating the largest allowable total-bundle data size to be received in this session. - Any bundle transfer sent to this peer SHALL have a Total bundle - data payload no longer than the peer's Transfer MRU. This value + Any bundle transfer sent to this peer SHALL have a Total Bundle + Length payload no longer than the peer's Transfer MRU. This value can be used to perform proactive bundle fragmentation. The two nodes of a single session MAY have different Transfer MRUs, and no relation between the two is required. EID Length and EID Data: Together these fields represent a variable- length text string. The EID Length is a 16-bit unsigned integer indicating the number of octets of EID Data to follow. A zero EID Length SHALL be used to indicate the lack of EID rather than a - truly empty EID. This case allows an node to avoid exposing EID + truly empty EID. This case allows a node to avoid exposing EID information on an untrusted network. A non-zero-length EID Data SHALL contain the UTF-8 encoded EID of some singleton endpoint in which the sending node is a member, in the canonical format of :. This EID encoding is consistent with [I-D.ietf-dtn-bpbis]. - Header Extension Length Header Extension Items: Together these + Header Extension Length and Header Extension Items: Together these fields represent protocol extension data not defined by this specification. The Header Extension Length is the total number of octets to follow which are used to encode the Header Extension - Item list. The encoding of each Header Extension Item is - identical form as described in Section 4.1.1. + Item list. The encoding of each Header Extension Item is within a + consistent data container as described in Section 4.2.1. +----------+--------+-----------------------------------------------+ | Name | Code | Description | +----------+--------+-----------------------------------------------+ | CAN_TLS | 0x01 | If bit is set, indicates that the sending | | | | peer is capable of TLS security. | | | | | | Reserved | others | +----------+--------+-----------------------------------------------+ Table 1: Contact Header Flags -4.1.1. Header Extension Items +4.2.1. Header Extension Items - Each of the Header Extension items SHALL be encoded in an identical + Each of the Header Extension Items SHALL be encoded in an identical Type-Length-Value (TLV) container form as indicated in Figure 4. The - fields of the header extension item are: + fields of the Header Extension Item are: Flags: A one-octet field containing generic bit flags about the - item, which are listed in Table 2. If a TCPCL node receives an - extension item with an unknown Item Type and the CRITICAL flag - set, the node SHALL close the TCPCL session with SHUTDOWN reason - code of "Contact Failure". If the CRITICAL flag is not set, an - node SHALL skip over and ignore any item with an unknown Item - Type. + Item, which are listed in Table 2. If a TCPCL node receives a + Header Extension Item with an unknown Item Type and the CRITICAL + flag set, the node SHALL close the TCPCL session with SHUTDOWN + reason code of "Contact Failure". If the CRITICAL flag is not + set, a node SHALL skip over and ignore any item with an unknown + Item Type. Item Type: A 16-bit unsigned integer field containing the type of the extension item. This specification does not define any extension types directly, but does allocate an IANA registry for such codes (see Section 8.3). Item Length: A 32-bit unsigned integer field containing the number of Item Value octets to follow. Item Value: A variable-length data field which is interpreted according to the associated Item Type. This specification places - no restrictions on an extensions use of available Item Value data. - Extension specification SHOULD avoid the use of large data - exchanges within the TCPCLv4 contact header as no bundle transfers - can begin until the a full contact exchange and negotiation has - been completed. + no restrictions on an extension's use of available Item Value + data. Extension specification SHOULD avoid the use of large data + exchanges within the TCPCL contact header as no bundle transfers + can begin until the full contact exchange and negotiation has been + completed. 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 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 +---------------+---------------+---------------+---------------+ | Item Flags | Item Type | Item Length...| +---------------+---------------+---------------+---------------+ | length contd. | Item Value... | +---------------+---------------+---------------+---------------+ | value contd. | +---------------+---------------+---------------+---------------+ - Figure 4: Header Extention Item Format + Figure 4: Header Extension Item Format +----------+--------+-----------------------------------------------+ | Name | Code | Description | +----------+--------+-----------------------------------------------+ | CRITICAL | 0x01 | If bit is set, indicates that the receiving | | | | peer must handle the extension item. | | | | | | Reserved | others | +----------+--------+-----------------------------------------------+ Table 2: Header Extension Item Flags -4.2. Validation and Parameter Negotiation +4.3. Validation and Parameter Negotiation Upon reception of the contact header, each node follows the following procedures to ensure the validity of the TCPCL session and to negotiate values for the session parameters. If the magic string is not present or is not valid, the connection MUST be terminated. The intent of the magic string is to provide some protection against an inadvertent TCP connection by a different protocol than the one described in this document. To prevent a flood of repeated connections from a misconfigured application, a node MAY @@ -591,106 +634,101 @@ node MAY attempt further TCPCL sessions with the peer using earlier protocol version numbers in decreasing order. Managing multi-TCPCL- session state such as this is an implementation matter. If a node receives a contact header containing a version that is greater than the current version of the protocol that the node implements, then the node SHALL shutdown the session with a reason code of "Version mismatch". If a node receives a contact header with a version that is lower than the version of the protocol that the node implements, the node MAY either terminate the session (with a - reason code of "Version mismatch"). Otherwise, the node MAY adapt - its operation to conform to the older version of the protocol. The + reason code of "Version mismatch") or the node MAY adapt its + operation to conform to the older version of the protocol. The decision of version fall-back is an implementation matter. A node calculates the parameters for a TCPCL session by negotiating the values from its own preferences (conveyed by the contact header it sent to the peer) with the preferences of the peer node (expressed in the contact header that it received from the peer). The negotiated parameters defined by this specification are described in the following paragraphs. + Transfer MTU and Segment MTU: The maximum transmit unit (MTU) for + whole transfers and individual segments are idententical to the + Transfer MRU and Segment MRU, respectively, of the recevied + contact header. A transmitting peer can send individual segments + with any size smaller than the Segment MTU, depending on local + policy, dynamic network conditions, etc. Determining the size of + each transmitted segment is an implementation matter. + Session Keepalive: Negotiation of the Session Keepalive parameter is performed by taking the minimum of this two contact headers' - Keepalive Interval. If the negotiated Session Keepalive is zero - (i.e. one or both contact headers contains a zero Keepalive - Interval), then the keepalive feature (described in Section 5.2.1) - is disabled. There is no logical minimum value for the keepalive - interval, but when used for many sessions on an open, shared - network a short interval could lead to excessive traffic. For - shared network use, nodes SHOULD choose a keepalive interval no - shorter than 30 seconds. There is no logical maximum value for - the keepalive interval, but an idle TCP connection is liable for - closure by the host operating system if the keepalive time is - longer than tens-of-minutes. Nodes SHOULD choose a keepalive - interval no longer than 10 minutes (600 seconds). + Keepalive Interval. The Session Keepalive interval is a parameter + for the behavior described in Section 5.2.1. Enable TLS: Negotiation of the Enable TLS parameter is performed by taking the logical AND of the two contact headers' CAN_TLS flags. - If the negotiated Enable TLS value is true then TLS negotiation - feature (described in Section 4.3) begins immediately following - the contact header exchange. The security policy on either node - MAY forbid the establishment of a TCPCL session for any Enable TLS - result (or for any combination of local or peer CAN_TLS flag), in - which case the node SHALL shutdown the session with a reason code - of "Contact Failure". For example, one node may disallow TCPCL - sessions without TLS, while a second node may disallow sessions - with TLS. Also note that this Contact Failure (of the header - negotiation) is different than a TLS Failure (after an agreed-upon - Enable TLS state). + A local security policy is then applied to determine of the + negotated value of Enable TLS is acceptable. If not, the node + SHALL shutdown the session with a reason code of "Contact + Failure". Note that this contact failure is different than a "TLS + Failure" after an agreed-upon and acceptable Enable TLS state. If + the negotiated Enable TLS value is true and acceptable then TLS + negotiation feature (described in Section 4.4) begins immediately + following the contact header exchange. Once this process of parameter negotiation is completed (which includes a possible completed TLS handshake of the connection to use TLS), this protocol defines no additional mechanism to change the parameters of an established session; to effect such a change, the TCPCL session MUST be terminated and a new session established. -4.3. Session Security +4.4. Session Security This version of the TCPCL supports establishing a Transport Layer - Security (TLS) session within an existing TCP connection. - Negotiation of whether or not to initiate TLS within a TCPCL session - is part of the contact header as described in Section 4.2. The TLS - handshake, if it occurs, is considered to be part of the contact - negotiation before the TCPCL session itself is established. - Specifics about sensitive data exposure are discussed in Section 7. + Security (TLS) session within an existing TCP connection. When TLS + is used within the TCPCL it affects the entire session. Once + established, there is no mechanism available to downgrade a TCPCL + session to non-TLS operation. If this is desired, the entire TCPCL + session MUST be shutdown and a new non-TLS-negotiated session + established. - When TLS is used within the TCPCL it affects the entire session. By - convention, this protocol uses the node which initiated the - underlying TCP connection as the "client" role of the TLS handshake - request. Once a TLS session is established within TCPCL, there is no - mechanism provided to end the TLS session and downgrade the session. - If a non-TLS session is desired after a TLS session is started then - the entire TCPCL session MUST be shutdown first. + The use of TLS is negotated using the Contact Header as described in + Section 4.3. After negotiating an Enable TLS parameter of true, and + before any other TCPCL messages are sent within the session, the + session nodes SHALL begin a TLS handshake in accordance with + [RFC5246]. The parameters within each TLS negotiation are + implementation dependent but any TCPCL node SHOULD follow all + recommended best practices of [RFC7525]. By convention, this + protocol uses the node which initiated the underlying TCP connection + as the "client" role of the TLS handshake request. - After negotiating an Enable TLS parameter of true, and before any - other TCPCL messages are sent within the session, the session nodes - SHALL begin a TLS handshake in accordance with [RFC5246]. The - parameters within each TLS nqion are implementation dependent but any - TCPCL node SHOULD follow all recommended best practices of [RFC7525]. + The TLS handshake, if it occurs, is considered to be part of the + contact negotiation before the TCPCL session itself is established. + Specifics about sensitive data exposure are discussed in Section 7. -4.3.1. TLS Handshake Result +4.4.1. TLS Handshake Result If a TLS handshake cannot negotiate a TLS session, both nodes of the - TCPCL session SHALL cause a TCPCL shutdown with reason "TLS Failure". + TCPCL session SHALL start a TCPCL shutdown with reason "TLS Failure". After a TLS session is successfully established, both TCPCL nodes SHALL re-exchange TCPCL Contact Header messages. Any information cached from the prior Contact Header exchange SHALL be discarded. - This re-exchange avoids man-in-the-middle attack in identical fashion - to [RFC2595]. Each re-exchange header CAN_TLS flag SHALL be + This re-exchange avoids a "man-in-the-middle" attack in identical + fashion to [RFC2595]. Each re-exchange header CAN_TLS flag SHALL be identical to the original header CAN_TLS flag from the same node. The CAN_TLS logic (TLS negotiation) SHALL NOT apply during header re- exchange. This reinforces the fact that there is no TLS downgrade mechanism. -4.3.2. Example TLS Initiation +4.4.2. Example TLS Initiation A summary of a typical CAN_TLS usage is shown in the sequence in Figure 5 below. Node A Node B ====== ====== +-------------------------+ | Open TCP Connnection | -> +-------------------------+ +-------------------------+ @@ -773,42 +811,49 @@ Table 3: TCPCL Message Types 5.2. Upkeep and Status Messages 5.2.1. Session Upkeep (KEEPALIVE) The protocol includes a provision for transmission of KEEPALIVE messages over the TCPCL session to help determine if the underlying TCP connection has been disrupted. - As described in Section 4.1, one of the parameters in the contact - header is the Keepalive Interval. Both sides populate this field - with their requested intervals (in seconds) between KEEPALIVE - messages. + As described in Section 4.3, a negotiated parameter of each session + is the Session Keepalive interval. If the negotiated Session + Keepalive is zero (i.e. one or both contact headers contains a zero + Keepalive Interval), then the keepalive feature is disabled. There + is no logical minimum value for the keepalive interval, but when used + for many sessions on an open, shared network a short interval could + lead to excessive traffic. For shared network use, nodes SHOULD + choose a keepalive interval no shorter than 30 seconds. There is no + logical maximum value for the keepalive interval, but an idle TCP + connection is liable for closure by the host operating system if the + keepalive time is longer than tens-of-minutes. Nodes SHOULD choose a + keepalive interval no longer than 10 minutes (600 seconds). + + Note: The Keepalive Interval SHOULD NOT be chosen too short as TCP + retransmissions MAY occur in case of packet loss. Those will have to + be triggered by a timeout (TCP retransmission timeout (RTO)), which + is dependent on the measured RTT for the TCP connection so that + KEEPALIVE messages MAY experience noticeable latency. The format of a KEEPALIVE message is a one-octet message type code of KEEPALIVE (as described in Table 3) with no additional data. Both sides SHOULD send a KEEPALIVE message whenever the negotiated interval has elapsed with no transmission of any message (KEEPALIVE or other). - If no message (KEEPALIVE or other) has been received for at least - twice the Keepalive Interval, then either party MAY terminate the - session by transmitting a one-octet SHUTDOWN message (as described in - Section 6.1) with reason code "Idle Timeout", and by closing the - session. - - Note: The Keepalive Interval SHOULD not be chosen too short as TCP - retransmissions MAY occur in case of packet loss. Those will have to - be triggered by a timeout (TCP retransmission timeout (RTO)), which - is dependent on the measured RTT for the TCP connection so that - KEEPALIVE messages MAY experience noticeable latency. + If no message (KEEPALIVE or other) has been received in a session + after some implementation-defined time duration, then the node MAY + terminate the session by transmitting a one-octet SHUTDOWN message + (as described in Section 6.1) with reason code "Idle Timeout. 5.2.2. Message Rejection (MSG_REJECT) If a TCPCL node receives a message which is unknown to it (possibly due to an unhandled protocol mismatch) or is inappropriate for the current session state (e.g. a KEEPALIVE message received after contact header negotiation has disabled that feature), there is a protocol-level message to signal this condition in the form of a MSG_REJECT reply. @@ -845,41 +890,50 @@ | | | | | Message | 0x03 | A message was received while the session is | | Unexpected | | in a state in which the message is not | | | | expected. | +-------------+------+----------------------------------------------+ Table 4: MSG_REJECT Reason Codes 5.3. Bundle Transfer - All of the message in this section are directly associated with + All of the messages in this section are directly associated with transferring a bundle between TCPCL nodes. A single TCPCL transfer results in a bundle (handled by the convergence layer as opaque data) being exchanged from one node to the other. In TCPCL a transfer is accomplished by dividing a single bundle up into "segments" based on the receiving-side Segment MRU - (see Section 4.1). + (see Section 4.2). The choice of the length to use for segments is + an implementation matter, but each segment MUST be no larger than the + receiving node's maximum receive unit (MRU) (see the field "Segment + MRU" of Section 4.2). The first segment for a bundle MUST set the + 'START' flag, and the last one MUST set the 'end' flag in the + XFER_SEGMENT message flags. A single transfer (and by extension a single segment) SHALL NOT contain data of more than a single bundle. This requirement is imposed on the agent using the TCPCL rather than TCPCL itself. + If multiple bundles are transmitted on a single TCPCL connection, + they MUST be transmitted consecutively without interleaving of + segments from multiple bundles. + 5.3.1. Bundle Transfer ID - Each of the bundle transfer messages contains a Transfer ID number - which is used to correlate messages originating from sender and - receiver of a bundle. A Transfer ID does not attempt to address - uniqueness of the bundle data itself and has no relation to concepts - such as bundle fragmentation. Each invocation of TCPCL by the bundle - protocol agent, requesting transmission of a bundle (fragmentary or + Each of the bundle transfer messages contains a Transfer ID which is + used to correlate messages (from both sides of a transfer) for each + bundle. A Transfer ID does not attempt to address uniqueness of the + bundle data itself and has no relation to concepts such as bundle + fragmentation. Each invocation of TCPCL by the bundle protocol + agent, requesting transmission of a bundle (fragmentary or otherwise), results in the initiation of a single TCPCL transfer. Each transfer entails the sending of a XFER_INIT message and some number of XFER_SEGMENT and XFER_ACK messages; all are correlated by the same Transfer ID. Transfer IDs from each node SHALL be unique within a single TCPCL session. The initial Transfer ID from each node SHALL have value zero. Subsequent Transfer ID values SHALL be incremented from the prior Transfer ID value by one. Upon exhaustion of the entire 64-bit Transfer ID space, the sending node SHALL terminate the session with @@ -907,42 +961,38 @@ value indicated by the XFER_INIT message, the receiver SHOULD treat the transmitted data as invalid. The format of the XFER_INIT message is as follows: +-----------------------------+ | Message Header | +-----------------------------+ | Transfer ID (U64) | +-----------------------------+ - | Total bundle length (U64) | + | Total Bundle Length (U64) | +-----------------------------+ Figure 8: Format of XFER_INIT Messages The fields of the XFER_INIT message are: Transfer ID: A 64-bit unsigned integer identifying the transfer about to begin. - Total bundle length: A 64-bit unsigned integer indicating the size + Total Bundle Length: A 64-bit unsigned integer indicating the size of the data-to-be-transferred. - An XFER_INIT message SHALL be sent immediately before transmission of - any XFER_SEGMENT messages for each Transfer ID. XFER_INIT messages - MUST NOT be sent unless the next XFER_SEGMENT message has the 'START' - bit set to "1" (i.e., just before the start of a new transfer). - - A receiver MAY send a BUNDLE_REFUSE message as soon as it receives a - XFER_INIT message without waiting for the next XFER_SEGMENT message. - The sender MUST be prepared for this and MUST associate the refusal - with the correct bundle via the Transfer ID fields. + An XFER_INIT message SHALL be sent as the first message in a transfer + sequence, before transmission of any XFER_SEGMENT messages for the + same Transfer ID. XFER_INIT messages MUST NOT be sent unless the + next XFER_SEGMENT message has the 'START' bit set to "1" (i.e., just + before the start of a new transfer). 5.3.3. Data Transmission (XFER_SEGMENT) Each bundle is transmitted in one or more data segments. The format of a XFER_SEGMENT message follows in Figure 9. +------------------------------+ | Message Header | +------------------------------+ | Message Flags (U8) | @@ -997,25 +1047,25 @@ transfers from the same node is possible within a single TCPCL session. Simultaneous transfers between two nodes MAY be achieved using multiple TCPCL sessions. 5.3.4. Data Acknowledgments (XFER_ACK) Although the TCP transport provides reliable transfer of data between transport peers, the typical BSD sockets interface provides no means to inform a sending application of when the receiving application has processed some amount of transmitted data. Thus, after transmitting - some data, a Bundle Protocol agent needs an additional mechanism to - determine whether the receiving agent has successfully received the - segment. To this end, the TCPCL protocol provides feedback messaging - whereby a receiving node transmits acknowledgments of reception of - data segments. + some data, the TCPCL needs an additional mechanism to determine + whether the receiving agent has successfully received the segment. + To this end, the TCPCL protocol provides feedback messaging whereby a + receiving node transmits acknowledgments of reception of data + segments. The format of an XFER_ACK message follows in Figure 10. +-----------------------------+ | Message Header | +-----------------------------+ | Message Flags (U8) | +-----------------------------+ | Transfer ID (U64) | +-----------------------------+ @@ -1028,52 +1078,60 @@ Message Flags: A one-octet field of single-bit flags, interpreted according to the descriptions in Table 5. Transfer ID: A 64-bit unsigned integer identifying the transfer being acknowledged. Acknowledged length: A 64-bit unsigned integer indicating the total number of octets in the transfer which are being acknowledged. - A receiving TCPCL endpoing SHALL send an XFER_ACK message in response - to each received XFER_SEGMENT message. The flags portion of the + A receiving TCPCL node SHALL send an XFER_ACK message in response to + each received XFER_SEGMENT message. The flags portion of the XFER_ACK header SHALL be set to match the corresponding DATA_SEGMENT message being acknowledged. The acknowledged length of each XFER_ACK contains the sum of the data length fields of all XFER_SEGMENT messages received so far in the course of the indicated transfer. + The sending node MAY transmit multiple XFER_SEGMENT messages without + necessarily waiting for the corresponding XFER_ACK responses. This + enables pipelining of messages on a channel. For example, suppose the sending node transmits four segments of bundle data with lengths 100, 200, 500, and 1000, respectively. After receiving the first segment, the node sends an acknowledgment of length 100. After the second segment is received, the node sends an acknowledgment of length 300. The third and fourth acknowledgments are of length 800 and 1800, respectively. 5.3.5. Transfer Refusal (XFER_REFUSE) - The TCPCL supports an mechanism by which a receiving node can - indicate to the sender that it does not want to receive the - corresponding bundle. To do so, upon receiving a XFER_INIT or - XFER_SEGMENT message, the node MAY transmit a XFER_REFUSE message. - As data segments and acknowledgments MAY cross on the wire, the - bundle that is being refused SHALL be identified by the Transfer ID - of the refusal. + The TCPCL supports a mechanism by which a receiving node can indicate + to the sender that it does not want to receive the corresponding + bundle. To do so, upon receiving a XFER_INIT or XFER_SEGMENT + message, the node MAY transmit a XFER_REFUSE message. As data + segments and acknowledgments MAY cross on the wire, the bundle that + is being refused SHALL be identified by the Transfer ID of the + refusal. There is no required relation between the Transfer MRU of a TCPCL node (which is supposed to represent a firm limitation of what the node will accept) and sending of a XFER_REFUSE message. A XFER_REFUSE can be used in cases where the agent's bundle storage is temporarily depleted or somehow constrained. A XFER_REFUSE can also be used after the bundle header or any bundle data is inspected by an agent and determined to be unacceptable. + A receiver MAY send an XFER_REFUSE message as soon as it receives a + XFER_INIT message without waiting for the next XFER_SEGMENT message. + The sender MUST be prepared for this and MUST associate the refusal + with the correct bundle via the Transfer ID fields. + The format of the XFER_REFUSE message is as follows: +-----------------------------+ | Message Header | +-----------------------------+ | Reason Code (U8) | +-----------------------------+ | Transfer ID (U64) | +-----------------------------+ @@ -1138,21 +1196,21 @@ transmitted by either node at any point following complete transmission of any other message. After sending a SHUTDOWN message, the sender of the message MAY send further acknowledgments (XFER_ACK or XFER_REFUSE) but no further data messages (XFER_INIT or XFER_SEGMENT). A receiving node SHOULD acknowledge all received data segments before sending a SHUTDOWN message to end the session. A transmitting node SHALL treat a SHUTDOWN message received mid- transfer (i.e. before the final acknowledgment) as a failure of the transfer. - After transmitting a SHUTDOWN message, an node MAY immediately close + After transmitting a SHUTDOWN message, a node MAY immediately close the associated TCP connection. Once the SHUTDOWN message is sent, any further received data on the TCP connection SHOULD be ignored. Any delay between request to terminate the TCP connection and actual closing of the connection (a "half-closed" state) MAY be ignored by the TCPCL node. The format of the SHUTDOWN message is as follows: +-----------------------------------+ | Message Header | @@ -1169,39 +1227,39 @@ The fields of the SHUTDOWN message are: Message Flags: A one-octet field of single-bit flags, interpreted according to the descriptions in Table 7. Reason Code: A one-octet refusal reason code interpreted according to the descriptions in Table 8. The Reason Code is present or absent as indicated by one of the flags. Reconnection Delay: A 16-bit unsigned integer indicating the desired - delay until further TCPCL sessions to the sending node. The - Reconnection Delay is present or absent as indicated by one of the - flags. + delay, in seconds, before re-attepmting a TCPCL session to the + sending node. The Reconnection Delay is present or absent as + indicated by one of the flags. +----------+--------+-----------------------------------------------+ | Name | Code | Description | +----------+--------+-----------------------------------------------+ | D | 0x01 | If bit is set, indicates that a Reconnection | | | | Delay field is present. | | | | | | R | 0x02 | If bit is set, indicates that a Reason Code | | | | field is present. | | | | | | Reserved | others | +----------+--------+-----------------------------------------------+ Table 7: SHUTDOWN Flags - It is possible for a node to convey additional information regarding + It is possible for a node to convey optional information regarding the reason for session termination. To do so, the node MUST set the 'R' bit in the message flags and transmit a one-octet reason code immediately following the message header. The specified values of the reason code are: +---------------+---------------------------------------------------+ | Name | Description | +---------------+---------------------------------------------------+ | Idle timeout | The session is being closed due to idleness. | | | | @@ -1216,46 +1274,40 @@ | | | | TLS Failure | The node failed to negotiate TLS session and | | | cannot continue the session. | | | | | Resource | The node has run into some resource limit and | | Exhaustion | cannot continue the session. | +---------------+---------------------------------------------------+ Table 8: SHUTDOWN Reason Codes - It is also possible to convey a requested reconnection delay to - indicate how long the other node MUST wait before attempting session - re-establishment. To do so, the node sets the 'D' bit in the message - flags and then transmits an 16-bit unsigned integer specifying the - requested delay, in seconds, following the message header (and - optionally, the SHUTDOWN reason code). The value 0 SHALL be - interpreted as an infinite delay, i.e., that the connecting node MUST - NOT re-establish the session. In contrast, if the node does not wish - to request a delay, it SHOULD omit the reconnection delay field (and - set the 'D' bit to zero). + If a node does not want its peer to reopen a connection immediately, + it SHALL set the 'D' bit in the flags and include a reconnection + delay to indicate when the peer is allowed to attempt another session + setup. The Reconnection Delay value 0 SHALL be interpreted as an + infinite delay, i.e., that the connecting node MUST NOT re-establish + the session. - A session shutdown MAY occur immediately after TCP connection - establishment or reception of a contact header (and prior to any - further data exchange). This MAY, for example, be used to notify - that the node is currently not able or willing to communicate. - However, a node MUST always send the contact header to its peer - before sending a SHUTDOWN message. + A session shutdown MAY occur immediately after transmission of a + contact header (and prior to any further message transmit). This + MAY, for example, be used to notify that the node is currently not + able or willing to communicate. However, a node MUST always send the + contact header to its peer before sending a SHUTDOWN message. - If either node terminates a session prematurely in this manner, it - SHOULD send a SHUTDOWN message and MUST indicate a reason code unless - the incoming connection did not include the magic string. If the - magic string was not present, a node SHOULD close the TCP connection - without sending a SHUTDOWN message. If a node does not want its peer - to reopen a connection immediately, it SHOULD set the 'D' bit in the - flags and include a reconnection delay to indicate when the peer is - allowed to attempt another session setup. + If reception of the contact header itself somehow fails (e.g. an + invalid "magic string" is recevied), a node SHOULD close the TCP + connection without sending a SHUTDOWN message. If the content of the + Header Extension Items data disagrees with the Header Extension + Length (i.e. the last Item claims to use more octets than are present + in the Header Extension Length), the reception of the contact header + is considered to have failed. If a session is to be terminated before a protocol message has completed being sent, then the node MUST NOT transmit the SHUTDOWN message but still SHOULD close the TCP connection. Each TCPCL message is contiguous in the octet stream and has no ability to be cut short and/or preempted by an other message. This is particularly important when large segment sizes are being transmitted; either entire XFER_SEGMENT is sent before a SHUTDOWN message or the connection is simply terminated mid-XFER_SEGMENT. @@ -1263,40 +1315,40 @@ The protocol includes a provision for clean shutdown of idle sessions. Determining the length of time to wait before closing idle sessions, if they are to be closed at all, is an implementation and configuration matter. If there is a configured time to close idle links and if no TCPCL messages (other than KEEPALIVE messages) has been received for at least that amount of time, then either node MAY terminate the session by transmitting a SHUTDOWN message indicating the reason code of - 'Idle timeout' (as described in Table 8). + "Idle timeout" (as described in Table 8). 7. Security Considerations One security consideration for this protocol relates to the fact that nodes present their endpoint identifier as part of the contact header exchange. It would be possible for a node to fake this value and present the identity of a singleton endpoint in which the node is not a member, essentially masquerading as another DTN node. If this identifier is used outside of a TLS-secured session or without further verification as a means to determine which bundles are transmitted over the session, then the node that has falsified its identity would be able to obtain bundles that it otherwise would not have. Therefore, a node SHALL NOT use the EID value of an unsecured contact header to derive a peer node's identity unless it can - corroborate it via other means. When TCPCL session security mandated - by a TCPCL peer, that peer SHALL transmit initial unsecured contact - header values indicated in Table 9 in order. These values avoid - unnecessarily leaking endpoing parameters and will be ignored when - secure contact header re-exchange occurs. + corroborate it via other means. When TCPCL session security is + mandated by a TCPCL peer, that peer SHALL transmit initial unsecured + contact header values indicated in Table 9 in order. These values + avoid unnecessarily leaking session parameters and will be ignored + when secure contact header re-exchange occurs. +--------------------+---------------------------------------------+ | Parameter | Value | +--------------------+---------------------------------------------+ | Flags | The USE_TLS flag is set. | | | | | Keepalive Interval | Zero, indicating no keepalive. | | | | | Segment MRU | Zero, indicating all segments are refused. | | | | @@ -1365,21 +1417,21 @@ | | | | Reference: | [RFC7242] | | | | | Port Number: | 4556 | +------------------------+-------------------------------------+ 8.2. Protocol Versions IANA has created, under the "Bundle Protocol" registry, a sub- registry titled "Bundle Protocol TCP Convergence-Layer Version - Numbers" and initialized it with the following table. The + Numbers" and initialize it with the following table. The registration procedure is RFC Required. +-------+-------------+---------------------+ | Value | Description | Reference | +-------+-------------+---------------------+ | 0 | Reserved | [RFC7242] | | | | | | 1 | Reserved | [RFC7242] | | | | | | 2 | Reserved | [RFC7242] | @@ -1391,21 +1443,21 @@ | 5-255 | Unassigned | +-------+-------------+---------------------+ 8.3. Header Extension Types EDITOR NOTE: sub-registry to-be-created upon publication of this specification. IANA will create, under the "Bundle Protocol" registry, a sub- registry titled "Bundle Protocol TCP Convergence-Layer Version 4 - Header Extension Types" and initialized it with the contents of + Header Extension Types" and initialize it with the contents of Table 10. The registration procedure is RFC Required within the lower range 0x0001--0x3fff. Values in the range 0x8000--0xffff are reserved for use on private networks for functions not published to the IANA. +----------------+--------------------------+ | Code | Message Type | +----------------+--------------------------+ | 0x0000 | Reserved | | | | @@ -1416,21 +1468,21 @@ Table 10: Header Extension Type Codes 8.4. Message Types EDITOR NOTE: sub-registry to-be-created upon publication of this specification. IANA will create, under the "Bundle Protocol" registry, a sub- registry titled "Bundle Protocol TCP Convergence-Layer Version 4 - Message Types" and initialized it with the contents of Table 11. The + Message Types" and initialize it with the contents of Table 11. The registration procedure is RFC Required. +-----------+--------------+ | Code | Message Type | +-----------+--------------+ | 0x00 | Reserved | | | | | 0x01 | XFER_SEGMENT | | | | | 0x02 | XFER_ACK | @@ -1450,21 +1502,21 @@ Table 11: Message Type Codes 8.5. XFER_REFUSE Reason Codes EDITOR NOTE: sub-registry to-be-created upon publication of this specification. IANA will create, under the "Bundle Protocol" registry, a sub- registry titled "Bundle Protocol TCP Convergence-Layer Version 4 - XFER_REFUSE Reason Codes" and initialized it with the contents of + XFER_REFUSE Reason Codes" and initialize it with the contents of Table 12. The registration procedure is RFC Required. +----------+---------------------------+ | Code | Refusal Reason | +----------+---------------------------+ | 0x0 | Unknown | | | | | 0x1 | Completed | | | | | 0x2 | No Resources | @@ -1478,71 +1530,73 @@ Table 12: XFER_REFUSE Reason Codes 8.6. SHUTDOWN Reason Codes EDITOR NOTE: sub-registry to-be-created upon publication of this specification. IANA will create, under the "Bundle Protocol" registry, a sub- registry titled "Bundle Protocol TCP Convergence-Layer Version 4 - SHUTDOWN Reason Codes" and initialized it with the contents of + SHUTDOWN Reason Codes" and initialize it with the contents of Table 13. The registration procedure is RFC Required. - +------------+------------------+ + +------------+---------------------+ | Code | Shutdown Reason | - +------------+------------------+ + +------------+---------------------+ | 0x00 | Idle timeout | | | | | 0x01 | Version mismatch | | | | | 0x02 | Busy | | | | | 0x03 | Contact Failure | | | | | 0x04 | TLS failure | | | | - | 0x05--0xFF | Unassigned | - +------------+------------------+ + | 0x05 | Resource Exhaustion | + | | | + | 0x06--0xFF | Unassigned | + +------------+---------------------+ Table 13: SHUTDOWN Reason Codes 8.7. MSG_REJECT Reason Codes EDITOR NOTE: sub-registry to-be-created upon publication of this specification. IANA will create, under the "Bundle Protocol" registry, a sub- registry titled "Bundle Protocol TCP Convergence-Layer Version 4 - MSG_REJECT Reason Codes" and initialized it with the contents of + MSG_REJECT Reason Codes" and initialize it with the contents of Table 14. The registration procedure is RFC Required. +-----------+----------------------+ | Code | Rejection Reason | +-----------+----------------------+ | 0x00 | reserved | | | | | 0x01 | Message Type Unknown | | | | | 0x02 | Message Unsupported | | | | | 0x03 | Message Unexpected | | | | | 0x04-0xFF | Unassigned | +-----------+----------------------+ Table 14: REJECT Reason Codes 9. Acknowledgments - This memo is based on comments on implementation of [RFC7242] - provided from Scott Burleigh. + This specification is based on comments on implementation of + [RFC7242] provided from Scott Burleigh. 10. References 10.1. Normative References [I-D.ietf-dtn-bpbis] Burleigh, S., Fall, K., and E. Birrane, "Bundle Protocol Version 7", draft-ietf-dtn-bpbis-10 (work in progress), November 2017. @@ -1636,21 +1690,21 @@ The areas in which extensions from [RFC7242] have been made as new messages and codes are: o Added contact negotiation failure SHUTDOWN reason code. o Added MSG_REJECT message to indicate an unknown or unhandled message was received. o Added TLS session security mechanism. - o Added TLS failure SHUTDOWN reason code. + o Added TLS failure and Resource Exhaustion SHUTDOWN reason code. Authors' Addresses Brian Sipos RKF Engineering Solutions, LLC 7500 Old Georgetown Road Suite 1275 Bethesda, MD 20814-6198 US