draft-ietf-v6ops-ipv6-ehs-packet-drops-08.txt   rfc9098.txt 
IPv6 Operations Working Group (v6ops) F. Gont Internet Engineering Task Force (IETF) F. Gont
Internet-Draft SI6 Networks Request for Comments: 9098 SI6 Networks
Intended status: Informational N. Hilliard Category: Informational N. Hilliard
Expires: December 13, 2021 INEX ISSN: 2070-1721 INEX
G. Doering G. Doering
SpaceNet AG SpaceNet AG
W. Kumari W. Kumari
Google Google
G. Huston G. Huston
APNIC APNIC
W. Liu W. Liu
Huawei Technologies Huawei Technologies
June 11, 2021 September 2021
Operational Implications of IPv6 Packets with Extension Headers Operational Implications of IPv6 Packets with Extension Headers
draft-ietf-v6ops-ipv6-ehs-packet-drops-08
Abstract Abstract
This document summarizes the operational implications of IPv6 This document summarizes the operational implications of IPv6
extension headers specified in the IPv6 protocol specification extension headers specified in the IPv6 protocol specification (RFC
(RFC8200), and attempts to analyze reasons why packets with IPv6 8200) and attempts to analyze reasons why packets with IPv6 extension
extension headers are often dropped in the public Internet. headers are often dropped in the public Internet.
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 informational purposes.
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 This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." 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.
This Internet-Draft will expire on December 13, 2021. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9098.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology
3. Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Disclaimer
4. Background Information . . . . . . . . . . . . . . . . . . . 3 4. Background Information
5. Previous Work on IPv6 Extension Headers . . . . . . . . . . . 5 5. Previous Work on IPv6 Extension Headers
6. Packet Forwarding Engine Constraints . . . . . . . . . . . . 7 6. Packet-Forwarding Engine Constraints
6.1. Recirculation . . . . . . . . . . . . . . . . . . . . . . 8 6.1. Recirculation
7. Requirement to Process Layer-3/layer-4 information in 7. Requirement to Process Layer 3 / Layer 4 Information in
Intermediate Systems . . . . . . . . . . . . . . . . . . . . 8 Intermediate Systems
7.1. ECMP and Hash-based Load-Sharing . . . . . . . . . . . . 8 7.1. ECMP and Hash-Based Load Sharing
7.2. Enforcing infrastructure ACLs . . . . . . . . . . . . . . 9 7.2. Enforcing Infrastructure ACLs
7.3. DDoS Management and Customer Requests for Filtering . . . 10 7.3. DDoS Management and Customer Requests for Filtering
7.4. Network Intrusion Detection and Prevention . . . . . . . 10 7.4. Network Intrusion Detection and Prevention
7.5. Firewalling . . . . . . . . . . . . . . . . . . . . . . . 11 7.5. Firewalling
8. Operational and Security Implications . . . . . . . . . . . . 12 8. Operational and Security Implications
8.1. Inability to Find Layer-4 Information . . . . . . . . . . 12 8.1. Inability to Find Layer 4 Information
8.2. Route-Processor Protection . . . . . . . . . . . . . . . 12 8.2. Route-Processor Protection
8.3. Inability to Perform Fine-grained Filtering . . . . . . . 12 8.3. Inability to Perform Fine-Grained Filtering
8.4. Security Concerns Associated with IPv6 Extension Headers 12 8.4. Security Concerns Associated with IPv6 Extension Headers
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 9. IANA Considerations
10. Security Considerations . . . . . . . . . . . . . . . . . . . 14 10. Security Considerations
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 11. References
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 11.1. Normative References
12.1. Normative References . . . . . . . . . . . . . . . . . . 14 11.2. Informative References
12.2. Informative References . . . . . . . . . . . . . . . . . 15 Acknowledgements
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses
1. Introduction 1. Introduction
IPv6 Extension Headers (EHs) allow for the extension of the IPv6 IPv6 extension headers (EHs) allow for the extension of the IPv6
protocol, and provide support for core functionality such as IPv6 protocol and provide support for core functionality such as IPv6
fragmentation. However, common implementation limitations suggest fragmentation. However, common implementation limitations suggest
that EHs present a challenge for IPv6 packet routing equipment and that EHs present a challenge for IPv6 packet routing equipment and
middle-boxes, and evidence exists that IPv6 packets with EHs are middleboxes, and evidence exists that IPv6 packets with EHs are
intentionally dropped in the public Internet in some circumstances. intentionally dropped in the public Internet in some circumstances.
This document has the following goals: This document has the following goals:
o Raise awareness about the operational and security implications of * Raise awareness about the operational and security implications of
IPv6 Extension Headers specified in [RFC8200], and present reasons IPv6 extension headers specified in [RFC8200] and present reasons
why some networks resort to intentionally dropping packets why some networks resort to intentionally dropping packets
containing IPv6 Extension Headers. containing IPv6 extension headers.
o Highlight areas where current IPv6 support by networking devices * Highlight areas where current IPv6 support by networking devices
maybe sub-optimal, such that the aforementioned support is may be suboptimal, such that the aforementioned support is
improved. improved.
o Highlight operational issues associated with IPv6 extension * Highlight operational issues associated with IPv6 extension
headers, such that those issues are considered in IETF headers, such that those issues are considered in IETF
standardization efforts. standardization efforts.
Section 4 provides background information about the IPv6 packet Section 4 of this document provides background information about the
structure and associated implications. Section 5 of this document IPv6 packet structure and associated implications. Section 5
summarizes the previous work that has been carried out in the area of summarizes previous work that has been carried out in the area of
IPv6 extension headers. Section 6 discusses packet forwarding engine IPv6 extension headers. Section 6 discusses packet-forwarding engine
constraints in contemporary routers. Section 7 discusses why constraints in contemporary routers. Section 7 discusses why
intermediate systems may need to access Layer-4 information to make a intermediate systems may need to access Layer 4 information to make a
forwarding decision. Finally, Section 8 discusses the operational forwarding decision. Finally, Section 8 discusses operational
implications of IPv6 EHs. implications of IPv6 EHs.
2. Terminology 2. Terminology
This document uses the term "intermediate system" to describe both This document uses the term "intermediate system" to describe both
routers and middle-boxes, when there is no need to distinguish routers and middleboxes when there is no need to distinguish between
between the two and where the important issue is that the device the two and where the important issue is that the device being
being discussed forwards packets. discussed forwards packets.
3. Disclaimer 3. Disclaimer
This document analyzes the operational challenges represented by This document analyzes the operational challenges represented by
packets that employ IPv6 Extension Headers, and documents some of the packets that employ IPv6 extension headers and documents some of the
operational reasons why these packets are often dropped in the public operational reasons why these packets are often dropped in the public
Internet. This document is not a recommendation to drop such Internet. This document is not a recommendation to drop such
packets, but rather an analysis of why they are currently dropped. packets, but rather an analysis of why they are currently dropped.
4. Background Information 4. Background Information
It is useful to compare the basic structure of IPv6 packets against It is useful to compare the basic structure of IPv6 packets against
that of IPv4 packets, and analyze the implications of the two that of IPv4 packets and analyze the implications of the two
different packet structures. different packet structures.
IPv4 packets have a variable-length header size, that allows for the IPv4 packets have a variable-length header size that allows for the
use of IPv4 "options" -- optional information that may be of use by use of IPv4 "options" -- optional information that may be of use to
nodes processing IPv4 packets. The IPv4 header length is specified nodes processing IPv4 packets. The IPv4 header length is specified
in the IHL header field of the mandatory IPv4 header, and must be in in the "Internet Header Length" (IHL) field of the mandatory IPv4
the range from 20 octets (the minimum IPv4 header size) to 60 octets header and must be in the range of 20 octets (the minimum IPv4 header
(accommodating at most 40 octets of options). The upper-layer size) to 60 octets, accommodating at most 40 octets of options. The
protocol type is specified via the "Protocol" field of the mandatory upper-layer protocol type is specified via the "Protocol" field of
IPv4 header. the mandatory IPv4 header.
Protocol, IHL Protocol, IHL
+--------+ +--------+
| | | |
| v | v
+------//-----+------------------------+ +------//-----+------------------------+
| | | | | |
| IPv4 | Upper-Layer | | IPv4 | Upper-Layer |
| Header | Protocol | | Header | Protocol |
| | | | | |
+-----//------+------------------------+ +-----//------+------------------------+
variable length variable length
<-------------> <------------->
Figure 1: IPv4 Packet Structure Figure 1: IPv4 Packet Structure
IPv6 took a different approach to the IPv6 packet structure. Rather IPv6 took a different approach to the IPv6 packet structure. Rather
than employing a variable-length header as IPv4 does, IPv6 employs a than employing a variable-length header as IPv4 does, IPv6 employs a
linked-list-like packet structure, where a mandatory fixed-length packet structure similar to a linked list, where a mandatory fixed-
IPv6 header is followed by an arbitrary number of optional extension length IPv6 header is followed by an arbitrary number of optional
headers, with the upper-layer header being the last header in the extension headers, with the upper-layer header being the last header
IPv6 header chain. Each extension header typically specifies its in the IPv6 header chain. Each extension header typically specifies
length (unless it is implicit from the extension header type), and its length (unless it is implicit from the extension header type) and
the "next header" type that follows in the IPv6 header chain. the "next header" (NH) type that follows in the IPv6 header chain.
NH NH, EH-length NH, EH-length NH NH, EH-length NH, EH-length
+-------+ +------+ +-------+ +-------+ +------+ +-------+
| | | | | | | | | | | |
| v | v | v | v | v | v
+-------------+-------------+-//-+---------------+--------------+ +-------------+-------------+-//-+---------------+--------------+
| | | | | | | | | | | |
| IPv6 | Ext. | | Ext. | Upper-Layer | | IPv6 | Ext. | | Ext. | Upper-Layer |
| header | Header | | Header | Protocol | | header | Header | | Header | Protocol |
| | | | | | | | | | | |
+-------------+-------------+-//-+---------------+--------------+ +-------------+-------------+-//-+---------------+--------------+
fixed length variable number of EHs & length fixed length variable number of EHs & length
<------------> <--------------------------------> <------------> <-------------------------------->
Figure 2: IPv6 Packet Structure Figure 2: IPv6 Packet Structure
This packet structure has the following implications: This packet structure has the following implications:
o [RFC8200] requires the entire IPv6 header chain to be contained in * [RFC8200] requires the entire IPv6 header chain to be contained in
the first fragment of a packet, therefore limiting the IPv6 the first fragment of a packet, therefore limiting the IPv6 header
extension header chain to the size of the path MTU. chain to the size of the path MTU.
o Other than the path MTU constraints, there are no other limits to * Other than the path MTU constraints, there are no other limits to
the number of IPv6 EHs that may be present in a packet. the number of IPv6 EHs that may be present in a packet.
Therefore, there is no upper-limit regarding "how deep into the Therefore, there is no upper limit regarding how deep into the
IPv6 packet" the upper-layer may be found. IPv6 packet the upper-layer protocol header may be found.
o The only way for a node to obtain the upper-layer protocol type or * The only way for a node to obtain the upper-layer protocol type or
find the upper-layer protocol header is to parse and process the find the upper-layer protocol header is to parse and process the
entire IPv6 header chain, in sequence, starting from the mandatory entire IPv6 header chain, in sequence, starting from the mandatory
IPv6 header, until the last header in the IPv6 header chain is IPv6 header until the last header in the IPv6 header chain is
found. found.
5. Previous Work on IPv6 Extension Headers 5. Previous Work on IPv6 Extension Headers
Some of the operational and security implications of IPv6 Extension Some of the operational and security implications of IPv6 extension
Headers have been discussed at the IETF: headers have been discussed in the IETF:
o [I-D.taylor-v6ops-fragdrop] discusses a rationale for which * [OPERATORS] discusses a rationale for which operators drop IPv6
operators drop IPv6 fragments. fragments.
o [I-D.wkumari-long-headers] discusses possible issues arising from * [HEADERS] discusses possible issues arising from "long" IPv6
"long" IPv6 header chains. header chains.
o [I-D.kampanakis-6man-ipv6-eh-parsing] describes how * [PARSING] describes how inconsistencies in the way IPv6 packets
inconsistencies in the way IPv6 packets with extension headers are with extension headers are parsed by different implementations
parsed by different implementations could result in evasion of could result in evasion of security controls and presents
security controls, and presents guidelines for parsing IPv6 guidelines for parsing IPv6 extension headers, with the goal of
extension headers with the goal of providing a common and providing a common and consistent parsing methodology for IPv6
consistent parsing methodology for IPv6 implementations. implementations.
o [I-D.ietf-opsec-ipv6-eh-filtering] analyzes the security * [IPV6-EH] analyzes the security implications of IPv6 EHs, as well
implications of IPv6 EHs, and the operational implications of as the operational implications of dropping packets that employ
dropping packets that employ IPv6 EHs and associated options. IPv6 EHs and associated options.
o [RFC7113] discusses how some popular RA-Guard implementations are * [RFC7113] discusses how some popular Router Advertisement Guard
subject to evasion by means of IPv6 extension headers. (RA-Guard) implementations are subject to evasion by means of IPv6
extension headers.
o [RFC8900] analyzes the fragility introduced by IP fragmentation. * [RFC8900] analyzes the fragility introduced by IP fragmentation.
A number of recent RFCs have discussed issues related to IPv6 A number of recent RFCs have discussed issues related to IPv6
extension headers, specifying updates to a previous revision of the extension headers and have specified updates to RFC 2460 [RFC2460]
IPv6 standard [RFC2460], many of which have now been incorporated (an earlier version of the IPv6 standard). Many of these updates
into the current IPv6 core standard [RFC8200] or the IPv6 Node have now been incorporated into the current IPv6 core standard
Requirements [RFC8504]. Namely, [RFC8200] or the IPv6 node requirements [RFC8504]. Namely,
o [RFC5095] discusses the security implications of Routing Header
Type 0 (RTH0), and deprecates it.
o [RFC5722] analyzes the security implications of overlapping * [RFC5095] discusses the security implications of Routing Header
fragments, and provides recommendations in this area. Type 0 (RHT0) and deprecates it.
o [RFC7045] clarifies how intermediate nodes should deal with IPv6 * [RFC5722] analyzes the security implications of overlapping
fragments and provides recommendations in this area.
* [RFC7045] clarifies how intermediate nodes should deal with IPv6
extension headers. extension headers.
o [RFC7112] discusses the issues arising in a specific fragmentation * [RFC7112] discusses the issues arising in a specific fragmentation
case where the IPv6 header chain is fragmented into two or more case where the IPv6 header chain is fragmented into two or more
fragments (and formally forbids such fragmentation). fragments and formally forbids such fragmentation.
o [RFC6946] discusses a flawed (but common) processing of the so- * [RFC6946] discusses a flawed (but common) processing of the so-
called IPv6 "atomic fragments", and specified improved processing called IPv6 "atomic fragments" and specifies improved processing
of such packets. of such packets.
o [RFC8021] deprecates the generation of IPv6 atomic fragments. * [RFC8021] deprecates the generation of IPv6 atomic fragments.
o [RFC8504] clarifies processing rules for packets with extension * [RFC8504] clarifies processing rules for packets with extension
headers, and also allows hosts to enforce limits on the number of headers and also allows hosts to enforce limits on the number of
options included in IPv6 EHs. options included in IPv6 EHs.
o [RFC7739] discusses the security implications of predictable * [RFC7739] discusses the security implications of predictable
fragment Identification values, and provides recommendations for fragment Identification values and provides recommendations for
the generation of these values. the generation of these values.
o [RFC6980] analyzes the security implications of employing IPv6 * [RFC6980] analyzes the security implications of employing IPv6
fragmentation with Neighbor Discovery for IPv6, and formally fragmentation with Neighbor Discovery for IPv6 and formally
recommends against such usage. recommends against such usage.
Additionally, [RFC8200] has relaxed the requirement that "all nodes Additionally, [RFC8200] has relaxed the requirement that "all nodes
examine and process the Hop-by-Hop Options header" from [RFC2460], by must examine and process the Hop-by-Hop Options header" from
specifying that only nodes that have been explicitly configured to [RFC2460], by specifying that only nodes that have been explicitly
process the Hop-by-Hop Options header are required to do so. configured to process the Hop-by-Hop Options header are required to
do so.
A number of studies have measured the extent to which packets A number of studies have measured the extent to which packets
employing IPv6 extension headers are dropped in the public Internet: employing IPv6 extension headers are dropped in the public Internet:
o [PMTUD-Blackholes] and [Linkova-Gont-IEPG90] presented some * [PMTUD-Blackholes] and [Linkova-Gont-IEPG90] present some
preliminary measurements regarding the extent to which packet preliminary measurements regarding the extent to which packets
containing IPv6 EHs are dropped in the public Internet. containing IPv6 EHs are dropped in the public Internet.
o [RFC7872] presents more comprehensive results and documents the * [RFC7872] presents more comprehensive results and documents the
methodology used to obtain these results. methodology used to obtain these results.
o [Huston-2017] and [Huston-2020] measured packet drops resulting * [Huston-2017] and [Huston-2020] measure packet drops resulting
from IPv6 fragmentation when communicating with DNS servers. from IPv6 fragmentation when communicating with DNS servers.
6. Packet Forwarding Engine Constraints 6. Packet-Forwarding Engine Constraints
Most contemporary carrier-grade routers use dedicated hardware, e.g. Most contemporary carrier-grade routers use dedicated hardware, e.g.,
application-specific integrated circuits (ASICs) or network Application-Specific Integrated Circuits (ASICs) or Network
processing units (NPUs), to determine how to forward packets across Processing Units (NPUs), to determine how to forward packets across
their internal fabrics (see [IEPG94-Scudder] and [APNIC-Scudder] for their internal fabrics (see [IEPG94-Scudder] and [APNIC-Scudder] for
details). One of the common methods of handling next-hop lookup is details). One common method of handling next-hop lookups is to send
to send a small portion of the ingress packet to a lookup engine with a small portion of the ingress packet to a lookup engine with
specialised hardware, e.g. ternary content-addressable memory (TCAM) specialized hardware, e.g., ternary content-addressable memory (TCAM)
or reduced latency dynamic random-access memory (RLDRAM), to or reduced latency dynamic random-access memory (RLDRAM), to
determine the packet's next-hop. Technical constraints mean that determine the packet's next hop. Technical constraints mean that
there is a trade-off between the amount of data sent to the lookup there is a trade-off between the amount of data sent to the lookup
engine and the overall packet forwarding rate of the lookup engine. engine and the overall packet-forwarding rate of the lookup engine.
If more data is sent, the lookup engine can inspect further into the If more data is sent, the lookup engine can inspect further into the
packet, but the overall packet forwarding rate of the system will be packet, but the overall packet-forwarding rate of the system will be
reduced. If less data is sent, the overall packet forwarding rate of reduced. If less data is sent, the overall packet-forwarding rate of
the router will be increased but the packet lookup engine may not be the router will be increased, but the packet lookup engine may not be
able to inspect far enough into a packet to determine how it should able to inspect far enough into a packet to determine how it should
be handled. be handled.
NOTE: | NOTE:
For example, some contemporary high-end routers are known to |
inspect up to 192 bytes, while others are known to parse up to 384 | For example, some contemporary high-end routers are known to
bytes of header. | inspect up to 192 bytes, while others are known to parse up
| to 384 bytes of header.
If a hardware forwarding engine on a contemporary router cannot make If a hardware-forwarding engine on a contemporary router cannot make
a forwarding decision about a packet because critical information is a forwarding decision about a packet because critical information is
not sent to the look-up engine, then the router will normally drop not sent to the lookup engine, then the router will normally drop the
the packet. Section 7 discusses some of the reasons for which a packet. Section 7 discusses some of the reasons for which a
contemporary router might need to access layer-4 information to make contemporary router might need to access Layer 4 information to make
a forwarding decision. a forwarding decision.
Historically, some packet forwarding engines punted packets of this Historically, some packet-forwarding engines punted packets of this
form to the control plane for more in-depth analysis, but this is kind to the control plane for more in-depth analysis, but this is
unfeasible on most contemporary router architectures as a result of unfeasible on most contemporary router architectures as a result of
the vast difference between the hardware forwarding capacity of the the vast difference between the hardware-based forwarding capacity of
router and processing capacity of the control plane and the size of the router and the processing capacity of the control plane and the
the management link which connects the control plane to the size of the management link that connects the control plane to the
forwarding plane. Other platforms may have a separate software forwarding plane. Other platforms may have a separate software-based
forwarding plane that is distinct both from the hardware forwarding forwarding plane that is distinct both from the hardware-based
plane and the control plane. However, the limited CPU resources of forwarding plane and the control plane. However, the limited CPU
this software-based forwarding plane, as well as the limited resources of this software-based forwarding plane, as well as the
bandwidth of the associated link results in similar throughput limited bandwidth of the associated link, results in similar
constraints. throughput constraints.
If an IPv6 header chain is sufficiently long that it exceeds the If an IPv6 header chain is sufficiently long such that it exceeds the
packet look-up capacity of the router, the router might be unable to packet lookup capacity of the router, the router might be unable to
determine how the packet should be handled, and thus could resort to determine how the packet should be handled and thus could resort to
dropping the packet. dropping the packet.
6.1. Recirculation 6.1. Recirculation
Although TLV chains are amenable to iterative processing on Although type-length-value (TLV) chains are amenable to iterative
architectures that have packet look-up engines with deep inspection processing on architectures that have packet lookup engines with deep
capabilities, some packet forwarding engines manage IPv6 Extension inspection capabilities, some packet-forwarding engines manage IPv6
Header chains using recirculation. This approach processes Extension header chains using recirculation. This approach processes extension
Headers one at a time: when processing on one Extension Header is headers one at a time: when processing on one extension header is
completed, the packet is looped back through the processing engine completed, the packet is looped back through the processing engine
again. This recirculation process continues repeatedly until there again. This recirculation process continues repeatedly until there
are no more Extension Headers left to be processed. are no more extension headers left to be processed.
Recirculation is typically used on packet forwarding engines with Recirculation is typically used on packet-forwarding engines with
limited look-up capability, because it allows arbitrarily long header limited lookup capability, because it allows arbitrarily long header
chains to be processed without the complexity and cost associated chains to be processed without the complexity and cost associated
with packet forwarding engines which have deep look-up capabilities. with packet-forwarding engines, which have deep lookup capabilities.
However, recirculation can impact the forwarding capacity of However, recirculation can impact the forwarding capacity of
hardware, as each packet will pass through the processing engine hardware, as each packet will pass through the processing engine
multiple times. Depending on configuration, the type of packets multiple times. Depending on configuration, the type of packets
being processed, and the hardware capabilities of the packet being processed, and the hardware capabilities of the packet-
forwarding engine, this could impact data-plane throughput forwarding engine, the data-plane throughput performance on the
performance on the router. router might be negatively affected.
7. Requirement to Process Layer-3/layer-4 information in Intermediate 7. Requirement to Process Layer 3 / Layer 4 Information in Intermediate
Systems Systems
The following subsections discuss some of the reasons for which The following subsections discuss some of the reasons for which
intermediate systems may need to process Layer-3/layer-4 information intermediate systems may need to process Layer 3 / Layer 4
to make a forwarding decision. information to make a forwarding decision.
7.1. ECMP and Hash-based Load-Sharing 7.1. ECMP and Hash-Based Load Sharing
In the case of equal cost multi-path (ECMP) load sharing, the In the case of Equal Cost Multipath (ECMP) load sharing, the
intermediate system needs to make a decision regarding which of its intermediate system needs to make a decision regarding which of its
interfaces to use to forward a given packet. Since round-robin usage interfaces to use to forward a given packet. Since round-robin usage
of the links is usually avoided to prevent packet reordering, of the links is usually avoided to prevent packet reordering,
forwarding engines need to use a mechanism that will consistently forwarding engines need to use a mechanism that will consistently
forward the same data streams down the same forwarding paths. Most forward the same data streams down the same forwarding paths. Most
forwarding engines achieve this by calculating a simple hash using an forwarding engines achieve this by calculating a simple hash using an
n-tuple gleaned from a combination of layer-2 through to layer-4 n-tuple gleaned from a combination of Layer 2 through to Layer 4
packet header information. This n-tuple will typically use the src/ protocol header information. This n-tuple will typically use the
dst MAC address, src/dst IP address, and if possible further layer-4 src/dst Media Access Control (MAC) addresses, src/dst IP addresses,
src/dst port information. and, if possible, further Layer 4 src/dst port information.
In the IPv6 world, flows are expected to be identified by means of In the IPv6 world, flows are expected to be identified by means of
the IPv6 Flow Label [RFC6437]. Thus, ECMP and Hash-based Load- the IPv6 "Flow Label" [RFC6437]. Thus, ECMP and hash-based load
Sharing should be possible without the need to process the entire sharing should be possible without the need to process the entire
IPv6 header chain to obtain upper-layer information to identify IPv6 header chain to obtain upper-layer information to identify
flows. [RFC7098] discusses how the IPv6 Flow Label can used to flows. [RFC7098] discusses how the IPv6 Flow Label can be used to
enhance layer 3/4 load distribution and balancing for large server enhance Layer 3/4 load distribution and balancing for large server
farms. farms.
Historically, many IPv6 implementations failed to set the Flow Label, Historically, many IPv6 implementations failed to set the Flow Label,
and hash-based ECMP/load-sharing devices also did not employ the Flow and hash-based ECMP/load-sharing devices also did not employ the Flow
Label for performing their task. While support of [RFC6437] is Label for performing their task. While support of [RFC6437] is
currently widespread for current versions of all popular host currently widespread for current versions of all popular host
implementations, there is still only marginal usage of the IPv6 Flow implementations, there is still only marginal usage of the IPv6 Flow
Label for ECMP and load balancing [Cunha-2020]. A contributing Label for ECMP and load balancing [Almeida-2020]. A contributing
factor could be the issues that have been found in host factor could be the issues that have been found in host
implementations and middle-boxes [Jaeggli-2018]. implementations and middleboxes [Jaeggli-2018].
Clearly, widespread support of [RFC6437] would relieve intermediate Clearly, widespread support of [RFC6437] would relieve intermediate
systems from having to process the entire IPv6 header chain, making systems from having to process the entire IPv6 header chain, making
Flow Label-based ECMP and Load-Sharing [RFC6438] feasible. Flow Label-based ECMP and load sharing [RFC6438] feasible.
If an intermediate system cannot determine consistent n-tuples for If an intermediate system cannot determine consistent n-tuples for
calculating flow hashes, data streams are more likely to end up being calculating flow hashes, data streams are more likely to end up being
distributed unequally across ECMP and load-shared links. This may distributed unequally across ECMP and load-shared links. This may
lead to packet drops or reduced performance. lead to packet drops or reduced performance.
7.2. Enforcing infrastructure ACLs 7.2. Enforcing Infrastructure ACLs
Infrastructure ACLs (iACLs) drop unwanted packets destined to a Infrastructure Access Control Lists (iACLs) drop unwanted packets
network's infrastructure. Typically, iACLs are deployed because destined to a network's infrastructure. Typically, iACLs are
external direct access to a network's infrastructure addresses is deployed because external direct access to a network's infrastructure
operationally unnecessary, and can be used for attacks of different addresses is operationally unnecessary and can be used for attacks of
sorts against router control planes. To this end, traffic usually different sorts against router control planes. To this end, traffic
needs to be differentiated on the basis of layer-3 or layer-4 usually needs to be differentiated on the basis of Layer 3 or Layer 4
criteria to achieve a useful balance of protection and functionality. criteria to achieve a useful balance of protection and functionality.
For example, an infrastructure may be configured with the following For example, an infrastructure may be configured with the following
policy: policy:
o Permit some amount of ICMP echo (ping) traffic towards a router's * Permit some amount of ICMP echo (ping) traffic towards a router's
addresses for troubleshooting. addresses for troubleshooting.
o Permit BGP sessions on the shared network of an exchange point * Permit BGP sessions on the shared network of an exchange point
(potentially differentiating between the amount of packets/seconds (potentially differentiating between the amount of packets/second
permitted for established sessions and connection establishment), permitted for established sessions and for connection
but do not permit other traffic from the same peer IP addresses. establishment), but do not permit other traffic from the same peer
IP addresses.
If a forwarding router cannot determine consistent n-tuples for If a forwarding router cannot determine consistent n-tuples for
calculating flow hashes, data streams are more likely to end up being calculating flow hashes, data streams are more likely to end up being
distributed unequally across ECMP and load-shared links. This may distributed unequally across ECMP and load-shared links. This may
lead to packet drops or reduced performance. lead to packet drops or reduced performance.
If a network cannot deploy infrastructure ACLs, then the security of If a network cannot deploy infrastructure ACLs, then the security of
the network may be compromised due to having more potential attack the network may be compromised as a result of the increased attack
vectors open. surface.
7.3. DDoS Management and Customer Requests for Filtering 7.3. DDoS Management and Customer Requests for Filtering
The case of customer DDoS protection and edge-to-core customer The case of customer Distributed Denial-of-Service (DDoS) protection
protection filters is similar in nature to the iACL protection. and edge-to-core customer protection filters is similar in nature to
Similar to iACL protection, layer-4 ACLs generally need to be applied the iACL protection. Similar to iACL protection, Layer 4 ACLs
as close to the edge of the network as possible, even though the generally need to be applied as close to the edge of the network as
intent is usually to protect the customer edge rather than the possible, even though the intent is usually to protect the customer
provider core. Application of layer-4 DDoS protection to a network edge rather than the provider core. Application of Layer 4 DDoS
edge is often automated using Flowspec [RFC8955] [RFC8956]. protection to a network edge is often automated using BGP Flowspec
[RFC8955] [RFC8956].
For example, a web site that normally only handled traffic on TCP For example, a website that normally only handles traffic on TCP
ports 80 and 443 could be subject to a volumetric DDoS attack using ports 80 and 443 could be subject to a volumetric DDoS attack using
NTP and DNS packets with randomised source IP address, thereby NTP and DNS packets with a randomized source IP address, thereby
rendering traditional [RFC5635] source-based real-time black hole rendering source-based remote triggered black hole [RFC5635]
mechanisms useless. In this situation, DDoS protection ACLs could be mechanisms useless. In this situation, ACLs that provide DDoS
configured to block all UDP traffic at the network edge without protection could be configured to block all UDP traffic at the
impairing the web server functionality in any way. Thus, being able network edge without impairing the web server functionality in any
to block arbitrary protocols at the network edge can avoid DDoS- way. Thus, being able to block arbitrary protocols at the network
related problems both in the provider network and on the customer edge can avoid DDoS-related problems both in the provider network and
edge link. on the customer edge link.
7.4. Network Intrusion Detection and Prevention 7.4. Network Intrusion Detection and Prevention
Network Intrusion Detection Systems (NIDS) examine network traffic Network Intrusion Detection Systems (NIDS) examine network traffic
and try to identify traffic patterns that can be correlated to and try to identify traffic patterns that can be correlated to
network-based attacks. These systems generally inspect application- network-based attacks. These systems generally attempt to inspect
layer traffic (if possible), but at the bare minimum inspect layer-4 application-layer traffic (if possible) but, at the bare minimum,
flows. When attack activity is inferred, the operator is notified of inspect Layer 4 flows. When attack activity is inferred, the
the potential intrusion attempt. operator is notified of the potential intrusion attempt.
Network Intrusion Prevention Systems (IPS) operate similarly to Network Intrusion Prevention Systems (IPS) operate similarly to
NIDS's, but they can also prevent intrusions by reacting to detected NIDSs, but they can also prevent intrusions by reacting to detected
attack attempts by e.g., triggering packet filtering policies at attack attempts by e.g., triggering packet filtering policies at
firewalls and other devices. firewalls and other devices.
Use of extension headers can be problematic for NIDS/IPS, since: Use of extension headers can be problematic for NIDS/IPS, since:
o Extension headers increase the complexity of resulting traffic, * Extension headers increase the complexity of resulting traffic and
and the associated work and system requirements to process it. the associated work and system requirements to process it.
o Use of unknown extension headers can prevent an NIDS/IPS from * Use of unknown extension headers can prevent a NIDS or IPS from
processing layer-4 information. processing Layer 4 information.
o Use of IPv6 fragmentation requires a stateful fragment-reassembly * Use of IPv6 fragmentation requires a stateful fragment-reassembly
operation, even for decoy traffic employing forged source operation, even for decoy traffic employing forged source
addresses (see e.g., [nmap]). addresses (see, e.g., [nmap]).
As a result, in order to increase the efficiency or effectiveness of As a result, in order to increase the efficiency or effectiveness of
these systems, packets employing IPv6 extension headers are often these systems, packets employing IPv6 extension headers are often
dropped at the network ingress point(s) of networks that deploy these dropped at the network ingress point(s) of networks that deploy these
systems. systems.
7.5. Firewalling 7.5. Firewalling
Firewalls enforce security policies by means of packet filtering. Firewalls enforce security policies by means of packet filtering.
These systems usually inspect layer-3 and layer-4 traffic, but can These systems usually inspect Layer 3 and Layer 4 traffic but can
often also examine application-layer traffic flows. often also examine application-layer traffic flows.
As with NIDS/IPS (Section 7.4), use of IPv6 extension headers can As with a NIDS or IPS (Section 7.4), use of IPv6 extension headers
represent a challenge to network firewalls, since: can represent a challenge to network firewalls, since:
o Extension headers increase the complexity of resulting traffic, * Extension headers increase the complexity of resulting traffic and
and the associated work and system requirements to process it, as the associated work and system requirements to process it, as
outlined in [Zack-FW-Benchmark]. outlined in [Zack-FW-Benchmark].
o Use of unknown extension headers can prevent firewalls from * Use of unknown extension headers can prevent firewalls from
processing layer-4 information. processing Layer 4 information.
o Use of IPv6 fragmentation requires a stateful fragment-reassembly * Use of IPv6 fragmentation requires a stateful fragment-reassembly
operation, even for decoy traffic employing forged source operation, even for decoy traffic employing forged source
addresses (see e.g., [nmap]). addresses (see, e.g., [nmap]).
Additionally, a common firewall filtering policy is the so-called Additionally, a common firewall filtering policy is the so-called
"default deny", where all traffic is blocked (by default), and only "default deny", where all traffic is blocked (by default), and only
expected traffic is added to an "allow/accept list". expected traffic is added to an "allow/accept list".
As a result, packets employing IPv6 extension headers are often As a result, packets employing IPv6 extension headers are often
dropped by network firewalls, either because of the challenges dropped by network firewalls, either because of the challenges
represented by extension headers or because the use of IPv6 extension represented by extension headers or because the use of IPv6 extension
headers has not been explicitly allowed. headers has not been explicitly allowed.
Note that although the data presented in [Zack-FW-Benchmark] were Note that although the data presented in [Zack-FW-Benchmark] was
several years old at the time of publication of this document, many several years old at the time of publication of this document, many
contemporary firewalls use comparable hardware and software contemporary firewalls use comparable hardware and software
architecture, and consequently the conclusions of this benchmark are architectures; consequently, the conclusions of this benchmark are
still relevant, despite its age. still relevant, despite its age.
8. Operational and Security Implications 8. Operational and Security Implications
8.1. Inability to Find Layer-4 Information 8.1. Inability to Find Layer 4 Information
As discussed in Section 7, intermediate systems that need to find the As discussed in Section 7, intermediate systems that need to find the
layer-4 header must process the entire IPv6 extension header chain. Layer 4 header must process the entire IPv6 header chain. When such
When such devices are unable to obtain the required information, the devices are unable to obtain the required information, the forwarding
forwarding device has the option to drop the packet unconditionally, device has the option to drop the packet unconditionally, forward the
forward the packet unconditionally, or process the packet outside the packet unconditionally, or process the packet outside the normal
normal forwarding path. Forwarding packets unconditionally will forwarding path. Forwarding packets unconditionally will usually
usually allow for the circumvention of security controls (see e.g., allow for the circumvention of security controls (see, e.g.,
Section 7.5), while processing packets outside of the normal Section 7.5), while processing packets outside of the normal
forwarding path will usually open the door to DoS attacks (see e.g., forwarding path will usually open the door to Denial-of-Service (DoS)
Section 6). Thus, in these scenarios, devices often simply resort to attacks (see, e.g., Section 6). Thus, in these scenarios, devices
dropping such packets unconditionally. often simply resort to dropping such packets unconditionally.
8.2. Route-Processor Protection 8.2. Route-Processor Protection
Most contemporary carrier-grade routers have a fast hardware-assisted Most contemporary carrier-grade routers have a fast hardware-assisted
forwarding plane and a loosely coupled control plane, connected forwarding plane and a loosely coupled control plane, connected
together with a link that has much less capacity than the forwarding together with a link that has much less capacity than the forwarding
plane could handle. Traffic differentiation cannot be performed by plane could handle. Traffic differentiation cannot be performed by
the control plane, because this would overload the internal link the control plane because this would overload the internal link
connecting the forwarding plane to the control plane. connecting the forwarding plane to the control plane.
The Hop-by-Hop Options header has been particularly challenging since The Hop-by-Hop Options header has been particularly challenging
in most circumstances, the corresponding packet is punted to the since, in most circumstances, the corresponding packet is punted to
control plane for processing. As a result, many operators drop IPv6 the control plane for processing. As a result, many operators drop
packets containing this extension header [RFC7872]. [RFC6192] IPv6 packets containing this extension header [RFC7872]. [RFC6192]
provides advice regarding protection of a router's control plane. provides advice regarding protection of a router's control plane.
8.3. Inability to Perform Fine-grained Filtering 8.3. Inability to Perform Fine-Grained Filtering
Some intermediate systems do not have support for fine-grained Some intermediate systems do not have support for fine-grained
filtering of IPv6 extension headers. For example, an operator that filtering of IPv6 extension headers. For example, an operator that
wishes to drop packets containing Routing Header Type 0 (RHT0), may wishes to drop packets containing RHT0 may only be able to filter on
only be able to filter on the extension header type (Routing Header). the extension header type (Routing Header). This could result in an
This could result in an operator enforcing a more coarse filtering operator enforcing a coarser filtering policy (e.g., "drop all
policy (e.g., "drop all packets containing a Routing Header" vs. packets containing a Routing Header" vs. "only drop packets that
"only drop packets that contain a Routing Header Type 0"). contain a Routing Header Type 0").
8.4. Security Concerns Associated with IPv6 Extension Headers 8.4. Security Concerns Associated with IPv6 Extension Headers
The security implications of IPv6 Extension Headers generally fall The security implications of IPv6 extension headers generally fall
into one or more of these categories: into one or more of these categories:
o Evasion of security controls * Evasion of security controls
o DoS due to processing requirements
o DoS due to implementation errors * DoS due to processing requirements
o Extension Header-specific issues * DoS due to implementation errors
* Issues specific to the extension header type
Unlike IPv4 packets where the upper-layer protocol can be trivially Unlike IPv4 packets where the upper-layer protocol can be trivially
found by means of the "IHL" ("Internet Header Length") IPv4 header found by means of the IHL field of the IPv4 header, the structure of
field, the structure of IPv6 packets is more flexible and complex. IPv6 packets is more flexible and complex. This can represent a
This can represent a challenge for devices that need to find this challenge for devices that need to find this information, since
information, since locating upper-layer protocol information requires locating upper-layer protocol information requires that all IPv6
that all IPv6 extension headers be examined. In turn, this presents extension headers be examined. In turn, this presents implementation
implementation difficulties, since some packet filtering mechanisms difficulties, since some packet-filtering mechanisms that require
that require upper-layer information (even if just the upper layer upper-layer information (even if just the upper-layer protocol type)
protocol type) can be trivially circumvented by inserting IPv6 can be trivially circumvented by inserting IPv6 extension headers
Extension Headers between the main IPv6 header and the upper layer between the main IPv6 header and the upper-layer protocol header.
protocol. [RFC7113] describes this issue for the RA-Guard case, but [RFC7113] describes this issue for the RA-Guard case, but the same
the same techniques could be employed to circumvent other IPv6 techniques could be employed to circumvent other IPv6 firewall and
firewall and packet filtering mechanisms. Additionally, packet-filtering mechanisms. Additionally, implementation
implementation inconsistencies in packet forwarding engines can inconsistencies in packet-forwarding engines can result in evasion of
result in evasion of security controls security controls [PARSING] [Atlasis2014] [BH-EU-2014].
[I-D.kampanakis-6man-ipv6-eh-parsing] [Atlasis2014] [BH-EU-2014].
Sometimes packets with IPv6 Extension Headers can impact throughput Sometimes, packets with IPv6 extension headers can impact throughput
performance on intermediate systems. Unless appropriate mitigations performance on intermediate systems. Unless appropriate mitigations
are put in place (e.g., packet dropping and/or rate-limiting), an are put in place (e.g., packet dropping and/or rate limiting), an
attacker could simply send a large amount of IPv6 traffic employing attacker could simply send a large amount of IPv6 traffic employing
IPv6 Extension Headers with the purpose of performing a Denial of IPv6 extension headers with the purpose of performing a DoS attack
Service (DoS) attack (see Section 6.1 and Section 8 for further (see Sections 6.1 and 8 for further details). The extent to which
details). performance is affected on these devices is implementation dependent.
NOTE: | NOTE:
In the most trivial case, a packet that includes a Hop-by-Hop |
Options header might go through the slow forwarding path, to be | In the most trivial case, a packet that includes a Hop-by-
processed by the router's CPU. Alternatively, a router configured | Hop Options header might go through the slow forwarding
to enforce an ACL based on upper-layer information (e.g., upper | path, to be processed by the router's CPU. Alternatively, a
layer protocol or TCP Destination Port) may need to process the | router configured to enforce an ACL based on upper-layer
entire IPv6 header chain in order to find the required | information (e.g., upper-layer protocol type or TCP
information, thereby causing the packet to be processed in the | Destination Port) may need to process the entire IPv6 header
slow path [Cisco-EH-Cons]. We note that, for obvious reasons, the | chain in order to find the required information, thereby
aforementioned performance issues can affect other devices such as | causing the packet to be processed in the slow path
firewalls, Network Intrusion Detection Systems (NIDS), etc. | [Cisco-EH-Cons]. We note that, for obvious reasons, the
[Zack-FW-Benchmark]. The extent to which performance is affected | aforementioned performance issues can affect devices such as
on these devices is implementation-dependent. | firewalls, NIDSs, etc. [Zack-FW-Benchmark].
IPv6 implementations, like all other software, tend to mature with IPv6 implementations, like all other software, tend to mature with
time and wide-scale deployment. While the IPv6 protocol itself has time and wide-scale deployment. While the IPv6 protocol itself has
existed for over 20 years, serious bugs related to IPv6 Extension existed for over 20 years, serious bugs related to IPv6 extension
Header processing continue to be discovered (see e.g., [Cisco-Frag], header processing continue to be discovered (see, e.g., [Cisco-Frag],
[Microsoft-SA], and [FreeBSD-SA]). Because there is currently little [Microsoft-SA], and [FreeBSD-SA]). Because there is currently little
operational reliance on IPv6 Extension headers, the corresponding operational reliance on IPv6 extension headers, the corresponding
code paths are rarely exercised, and there is the potential for bugs code paths are rarely exercised, and there is the potential for bugs
that still remain to be discovered in some implementations. that still remain to be discovered in some implementations.
IPv6 Fragment Headers are employed to allow fragmentation of IPv6 The IPv6 Fragment Header is employed for the fragmentation and
packets. While many of the security implications of the reassembly of IPv6 packets. While many of the security implications
fragmentation / reassembly mechanism are known from the IPv4 world, of the fragmentation/reassembly mechanism are known from the IPv4
several related issues have crept into IPv6 implementations. These world, several related issues have crept into IPv6 implementations.
range from denial of service attacks to information leakage, as These range from DoS attacks to information leakages, as discussed in
discussed in [RFC7739], [Bonica-NANOG58] and [Atlasis2012]). [RFC7739], [Bonica-NANOG58], and [Atlasis2012].
9. IANA Considerations 9. IANA Considerations
This document has no IANA actions. This document has no IANA actions.
10. Security Considerations 10. Security Considerations
The security implications of IPv6 extension headers are discussed in The security implications of IPv6 extension headers are discussed in
Section 8.4. This document does not introduce any new security Section 8.4. This document does not introduce any new security
issues. issues.
11. Acknowledgements 11. References
The authors would like to thank (in alphabetical order) Mikael
Abrahamsson, Fred Baker, Dale W. Carder, Brian Carpenter, Tim Chown,
Owen DeLong, Gorry Fairhurst, Guillermo Gont, Tom Herbert, Lee
Howard, Tom Petch, Sander Steffann, Eduard Vasilenko, Eric Vyncke,
Rob Wilton, Jingrong Xie, and Andrew Yourtchenko, for providing
valuable comments on earlier versions of this document.
Fernando Gont would like to thank Jan Zorz / Go6 Lab
<https://go6lab.si/>, Jared Mauch, and Sander Steffann
<https://steffann.nl/>, for providing access to systems and networks
that were employed to perform experiments and measurements involving
packets with IPv6 Extension Headers.
12. References
12.1. Normative References 11.1. Normative References
[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation [RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
of Type 0 Routing Headers in IPv6", RFC 5095, of Type 0 Routing Headers in IPv6", RFC 5095,
DOI 10.17487/RFC5095, December 2007, DOI 10.17487/RFC5095, December 2007,
<https://www.rfc-editor.org/info/rfc5095>. <https://www.rfc-editor.org/info/rfc5095>.
[RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments", [RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments",
RFC 5722, DOI 10.17487/RFC5722, December 2009, RFC 5722, DOI 10.17487/RFC5722, December 2009,
<https://www.rfc-editor.org/info/rfc5722>. <https://www.rfc-editor.org/info/rfc5722>.
skipping to change at page 15, line 37 skipping to change at line 687
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200, (IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017, DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>. <https://www.rfc-editor.org/info/rfc8200>.
[RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node [RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504, Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
January 2019, <https://www.rfc-editor.org/info/rfc8504>. January 2019, <https://www.rfc-editor.org/info/rfc8504>.
12.2. Informative References 11.2. Informative References
[Almeida-2020]
Almeida, R., Cunha, I., Teixeira, R., Veitch, D., and C.
Diot, "Classification of Load Balancing in the Internet",
IEEE INFOCOM 2020, DOI 10.1109/INFOCOM41043.2020.9155387,
July 2020, <https://homepages.dcc.ufmg.br/~cunha/papers/
almeida20infocom-mca.pdf>.
[APNIC-Scudder] [APNIC-Scudder]
Scudder, J., "Modern router architecture and IPv6", APNIC Scudder, J., "Modern router architecture and IPv6", APNIC
Blog, June 4, 2020, <https://blog.apnic.net/2020/06/04/ Blog, June 2020, <https://blog.apnic.net/2020/06/04/
modern-router-architecture-and-ipv6/>. modern-router-architecture-and-ipv6/>.
[Atlasis2012] [Atlasis2012]
Atlasis, A., "Attacking IPv6 Implementation Using Atlasis, A., "Attacking IPv6 Implementation Using
Fragmentation", BlackHat Europe 2012. Amsterdam, Fragmentation", Black Hat Europe 2012, March 2012,
Netherlands. March 14-16, 2012, <https://void.gr/kargig/ipv6/bh-eu-12-Atlasis-
<https://media.blackhat.com/bh-eu-12/Atlasis/bh-eu-12- Attacking_IPv6-Slides.pdf>.
Atlasis-Attacking_IPv6-Slides.pdf>.
[Atlasis2014] [Atlasis2014]
Atlasis, A., "A Novel Way of Abusing IPv6 Extension Atlasis, A., "A Novel Way of Abusing IPv6 Extension
Headers to Evade IPv6 Security Devices", May 2014, Headers to Evade IPv6 Security Devices", May 2014,
<http://www.insinuator.net/2014/05/a-novel-way-of-abusing- <http://www.insinuator.net/2014/05/a-novel-way-of-abusing-
ipv6-extension-headers-to-evade-ipv6-security-devices/>. ipv6-extension-headers-to-evade-ipv6-security-devices/>.
[BH-EU-2014] [BH-EU-2014]
Atlasis, A., Rey, E., and R. Schaefer, "Evasion of High- Atlasis, A., Rey, E., and R. Schaefer, "Evasion of High-
End IDPS Devices at the IPv6 Era", BlackHat Europe 2014, End IDPS Devices at the IPv6 Era", Black Hat Europe 2014,
2014, <https://www.ernw.de/download/eu-14-Atlasis-Rey- 2014, <https://www.ernw.de/download/eu-14-Atlasis-Rey-
Schaefer-briefings-Evasion-of-HighEnd-IPS-Devices-wp.pdf>. Schaefer-briefings-Evasion-of-HighEnd-IPS-Devices-wp.pdf>.
[Bonica-NANOG58] [Bonica-NANOG58]
Bonica, R., "IPV6 FRAGMENTATION: The Case For Bonica, R., "IPv6 Fragmentation: The Case For
Deprecation", NANOG 58. New Orleans, Louisiana, USA. June Deprecation", NANOG 58, June 2013,
3-5, 2013, <https://www.nanog.org/sites/default/files/ <https://www.nanog.org/sites/default/files/
mon.general.fragmentation.bonica.pdf>. mon.general.fragmentation.bonica.pdf>.
[Cisco-EH-Cons] [Cisco-EH-Cons]
Cisco, "IPv6 Extension Headers Review and Considerations", Cisco, "IPv6 Extension Headers Review and Considerations",
October 2006, October 2006,
<http://www.cisco.com/en/US/technologies/tk648/tk872/ <http://www.cisco.com/en/US/technologies/tk648/tk872/
technologies_white_paper0900aecd8054d37d.pdf>. technologies_white_paper0900aecd8054d37d.pdf>.
[Cisco-Frag] [Cisco-Frag]
Cisco, "Cisco IOS XR Software Crafted IPv6 Packet Denial Cisco, "Cisco IOS XR Software Crafted IPv6 Packet Denial
of Service Vulnerability", June 2015, of Service Vulnerability", June 2015,
<http://tools.cisco.com/security/center/content/ <http://tools.cisco.com/security/center/content/
CiscoSecurityAdvisory/cisco-sa-20150611-iosxr>. CiscoSecurityAdvisory/cisco-sa-20150611-iosxr>.
[Cunha-2020]
Cunha, I., "IPv4 vs IPv6 load balancing in Internet
routes", NPS/CAIDA 2020 Virtual IPv6 Workshop, 2020,
<https://www.cmand.org/workshops/202006-v6/slides/
cunha.pdf>.
[FreeBSD-SA] [FreeBSD-SA]
FreeBSD, "FreeBSD Security Advisory FreeBSD-SA-20:24.ipv6: The FreeBSD Project, "IPv6 Hop-by-Hop options use-after-
IPv6 Hop-by-Hop options use-after-free bug", September free bug", September 2020,
2020, <https://www.freebsd.org/security/advisories/ <https://www.freebsd.org/security/advisories/FreeBSD-SA-
FreeBSD-SA-20:24.ipv6.asc>. 20:24.ipv6.asc>.
[HEADERS] Kumari, W., Jaeggli, J., Bonica, R. P., and J. Linkova,
"Operational Issues Associated With Long IPv6 Header
Chains", Work in Progress, Internet-Draft, draft-wkumari-
long-headers-03, 16 June 2015,
<https://datatracker.ietf.org/doc/html/draft-wkumari-long-
headers-03>.
[Huston-2017] [Huston-2017]
Huston, G., "Dealing with IPv6 fragmentation in the Huston, G., "Dealing with IPv6 fragmentation in the DNS",
DNS", APNIC Blog, 2017, APNIC Blog, August 2017,
<https://blog.apnic.net/2017/08/22/dealing-ipv6- <https://blog.apnic.net/2017/08/22/dealing-ipv6-
fragmentation-dns/>. fragmentation-dns/>.
[Huston-2020] [Huston-2020]
Huston, G., "Measurement of IPv6 Extension Header Huston, G., "Measurement of IPv6 Extension Header
Support", NPS/CAIDA 2020 Virtual IPv6 Workshop, 2020, Support", NPS/CAIDA 2020 Virtual IPv6 Workshop, June 2020,
<https://www.cmand.org/workshops/202006-v6/ <https://www.cmand.org/workshops/202006-v6/
slides/2020-06-16-xtn-hdrs.pdf>. slides/2020-06-16-xtn-hdrs.pdf>.
[I-D.ietf-opsec-ipv6-eh-filtering]
Gont, F. and W. Liu, "Recommendations on the Filtering of
IPv6 Packets Containing IPv6 Extension Headers at Transit
Routers", draft-ietf-opsec-ipv6-eh-filtering-07 (work in
progress), January 2021.
[I-D.kampanakis-6man-ipv6-eh-parsing]
Kampanakis, P., "Implementation Guidelines for parsing
IPv6 Extension Headers", draft-kampanakis-6man-ipv6-eh-
parsing-01 (work in progress), August 2014.
[I-D.taylor-v6ops-fragdrop]
Jaeggli, J., Colitti, L., Kumari, W., Vyncke, E., Kaeo,
M., and T. Taylor, "Why Operators Filter Fragments and
What It Implies", draft-taylor-v6ops-fragdrop-02 (work in
progress), December 2013.
[I-D.wkumari-long-headers]
Kumari, W., Jaeggli, J., Bonica, R. P., and J. Linkova,
"Operational Issues Associated With Long IPv6 Header
Chains", draft-wkumari-long-headers-03 (work in progress),
June 2015.
[IEPG94-Scudder] [IEPG94-Scudder]
Petersen, B. and J. Scudder, "Modern Router Architecture Petersen, B. and J. Scudder, "Modern Router Architecture
for Protocol Designers", IEPG 94. Yokohama, Japan. for Protocol Designers", IEPG 94, November 2015,
November 1, 2015, <http://www.iepg.org/2015-11-01-ietf94/ <http://www.iepg.org/2015-11-01-ietf94/IEPG-
IEPG-RouterArchitecture-jgs.pdf>. RouterArchitecture-jgs.pdf>.
[IPV6-EH] Gont, F. and W. Liu, "Recommendations on the Filtering of
IPv6 Packets Containing IPv6 Extension Headers at Transit
Routers", Work in Progress, Internet-Draft, draft-ietf-
opsec-ipv6-eh-filtering-08, 3 June 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-opsec-
ipv6-eh-filtering-08>.
[Jaeggli-2018] [Jaeggli-2018]
Jaeggli, J., "IPv6 flow label: misuse in hashing", APNIC Jaeggli, J., "IPv6 flow label: misuse in hashing", APNIC
Blog, 2018, <https://blog.apnic.net/2018/01/11/ipv6-flow- Blog, January 2018, <https://blog.apnic.net/2018/01/11/
label-misuse-hashing/>. ipv6-flow-label-misuse-hashing/>.
[Linkova-Gont-IEPG90] [Linkova-Gont-IEPG90]
Linkova, J. and F. Gont, "IPv6 Extension Headers in the Linkova, J. and F. Gont, "IPv6 Extension Headers in the
Real World v2.0", IEPG 90. Toronto, ON, Canada. July 20, Real World v2.0", IEPG 90, July 2014,
2014, <http://www.iepg.org/2014-07-20-ietf90/iepg- <http://www.iepg.org/2014-07-20-ietf90/iepg-ietf90-ipv6-
ietf90-ipv6-ehs-in-the-real-world-v2.0.pdf>. ehs-in-the-real-world-v2.0.pdf>.
[Microsoft-SA] [Microsoft-SA]
Microsoft, "Windows TCP/IP Remote Code Execution Microsoft, "Windows TCP/IP Remote Code Execution
Vulnerability (CVE-2021-24094)", February 2021, Vulnerability", CVE-2021-24094, February 2021,
<https://msrc.microsoft.com/update-guide/vulnerability/ <https://msrc.microsoft.com/update-guide/vulnerability/
CVE-2021-24094>. CVE-2021-24094>.
[nmap] Fyodor, "Dealing with IPv6 fragmentation in the [nmap] Lyon, G., "Firewall/IDS Evasion and Spoofing", Chapter 15.
DNS", Firewall/IDS Evasion and Spoofing, Nmap Reference Guide,
<https://nmap.org/book/man-bypass-firewalls-ids.html>. <https://nmap.org/book/man-bypass-firewalls-ids.html>.
[OPERATORS]
Jaeggli, J., Colitti, L., Kumari, W., Vyncke, E., Kaeo,
M., and T. Taylor, Ed., "Why Operators Filter Fragments
and What It Implies", Work in Progress, Internet-Draft,
draft-taylor-v6ops-fragdrop-02, 3 December 2013,
<https://datatracker.ietf.org/doc/html/draft-taylor-v6ops-
fragdrop-02>.
[PARSING] Kampanakis, P., "Implementation Guidelines for Parsing
IPv6 Extension Headers", Work in Progress, Internet-Draft,
draft-kampanakis-6man-ipv6-eh-parsing-01, 5 August 2014,
<https://datatracker.ietf.org/doc/html/draft-kampanakis-
6man-ipv6-eh-parsing-01>.
[PMTUD-Blackholes] [PMTUD-Blackholes]
De Boer, M. and J. Bosma, "Discovering Path MTU black De Boer, M. and J. Bosma, "Discovering Path MTU black
holes on the Internet using RIPE Atlas", July 2012, holes on the Internet using RIPE Atlas", University of
Amsterdam, MSc. Systems & Network Engineering, July 2012,
<http://www.nlnetlabs.nl/downloads/publications/pmtu- <http://www.nlnetlabs.nl/downloads/publications/pmtu-
black-holes-msc-thesis.pdf>. black-holes-msc-thesis.pdf>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <https://www.rfc-editor.org/info/rfc2460>. December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC5635] Kumari, W. and D. McPherson, "Remote Triggered Black Hole [RFC5635] Kumari, W. and D. McPherson, "Remote Triggered Black Hole
Filtering with Unicast Reverse Path Forwarding (uRPF)", Filtering with Unicast Reverse Path Forwarding (uRPF)",
RFC 5635, DOI 10.17487/RFC5635, August 2009, RFC 5635, DOI 10.17487/RFC5635, August 2009,
skipping to change at page 19, line 37 skipping to change at line 882
RFC 8955, DOI 10.17487/RFC8955, December 2020, RFC 8955, DOI 10.17487/RFC8955, December 2020,
<https://www.rfc-editor.org/info/rfc8955>. <https://www.rfc-editor.org/info/rfc8955>.
[RFC8956] Loibl, C., Ed., Raszuk, R., Ed., and S. Hares, Ed., [RFC8956] Loibl, C., Ed., Raszuk, R., Ed., and S. Hares, Ed.,
"Dissemination of Flow Specification Rules for IPv6", "Dissemination of Flow Specification Rules for IPv6",
RFC 8956, DOI 10.17487/RFC8956, December 2020, RFC 8956, DOI 10.17487/RFC8956, December 2020,
<https://www.rfc-editor.org/info/rfc8956>. <https://www.rfc-editor.org/info/rfc8956>.
[Zack-FW-Benchmark] [Zack-FW-Benchmark]
Zack, E., "Firewall Security Assessment and Benchmarking Zack, E., "Firewall Security Assessment and Benchmarking
IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1, IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1, June
Berlin, Germany. June 30, 2013, 2013, <https://www.ipv6hackers.org/files/meetings/ipv6-
<https://www.ipv6hackers.org/files/meetings/ipv6-hackers- hackers-1/zack-ipv6hackers1-firewall-security-assessment-
1/zack-ipv6hackers1-firewall-security-assessment-and- and-benchmarking.pdf>.
benchmarking.pdf>.
Acknowledgements
The authors would like to thank (in alphabetical order) Mikael
Abrahamsson, Fred Baker, Dale W. Carder, Brian Carpenter, Tim Chown,
Owen DeLong, Gorry Fairhurst, Guillermo Gont, Tom Herbert, Lee
Howard, Tom Petch, Sander Steffann, Eduard Vasilenko, √Čric Vyncke,
Rob Wilton, Jingrong Xie, and Andrew Yourtchenko for providing
valuable comments on earlier draft versions of this document.
Fernando Gont would like to thank Jan Zorz / Go6 Lab
<https://go6lab.si/>, Jared Mauch, and Sander Steffann
<https://steffann.nl/> for providing access to systems and networks
that were employed to perform experiments and measurements involving
packets with IPv6 extension headers.
Authors' Addresses Authors' Addresses
Fernando Gont Fernando Gont
SI6 Networks SI6 Networks
Segurola y Habana 4310, 7mo Piso Segurola y Habana 4310, 7mo Piso
Villa Devoto, Ciudad Autonoma de Buenos Aires Villa Devoto
Ciudad Autonoma de Buenos Aires
Argentina Argentina
Email: fgont@si6networks.com Email: fgont@si6networks.com
URI: https://www.si6networks.com URI: https://www.si6networks.com
Nick Hilliard Nick Hilliard
INEX INEX
4027 Kingswood Road 4027 Kingswood Road
Dublin 24 Dublin
IE 24
Ireland
Email: nick@inex.ie Email: nick@inex.ie
Gert Doering Gert Doering
SpaceNet AG SpaceNet AG
Joseph-Dollinger-Bogen 14 Joseph-Dollinger-Bogen 14
Muenchen D-80807 D-80807 Muenchen
Germany Germany
Email: gert@space.net Email: gert@space.net
Warren Kumari Warren Kumari
Google Google
1600 Amphitheatre Parkway 1600 Amphitheatre Parkway
Mountain View, CA 94043 Mountain View, CA 94043
US United States of America
Email: warren@kumari.net Email: warren@kumari.net
Geoff Huston Geoff Huston
Email: gih@apnic.net Email: gih@apnic.net
URI: http://www.apnic.net URI: https://www.apnic.net
Will (Shucheng) Liu Will (Shucheng) Liu
Huawei Technologies Huawei Technologies
Bantian, Longgang District Bantian, Longgang District
Shenzhen 518129 Shenzhen
P.R. China 518129
China
Email: liushucheng@huawei.com Email: liushucheng@huawei.com
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