< draft-ietf-v6ops-ipv6-ehs-packet-drops-01.txt   draft-ietf-v6ops-ipv6-ehs-packet-drops-02.txt >
IPv6 Operations Working Group (v6ops) F. Gont IPv6 Operations Working Group (v6ops) F. Gont
Internet-Draft SI6 Networks Internet-Draft SI6 Networks
Intended status: Informational N. Hilliard Intended status: Informational N. Hilliard
Expires: April 17, 2021 INEX Expires: June 8, 2021 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
October 14, 2020 December 5, 2020
Operational Implications of IPv6 Packets with Extension Headers Operational Implications of IPv6 Packets with Extension Headers
draft-ietf-v6ops-ipv6-ehs-packet-drops-01 draft-ietf-v6ops-ipv6-ehs-packet-drops-02
Abstract Abstract
This document summarizes the operational implications of IPv6 This document summarizes the operational implications of IPv6
extension headers, and attempts to analyze reasons why packets with extension headers specified in the IPv6 protocol specification
IPv6 extension headers may be dropped in the public Internet. (RFC8200), and attempts to analyze reasons why packets with IPv6
extension 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 Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 17, 2021. This Internet-Draft will expire on June 8, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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6.3. DDoS Management and Customer Requests for Filtering . . . 9 6.3. DDoS Management and Customer Requests for Filtering . . . 9
6.4. Network Intrusion Detection and Prevention . . . . . . . 10 6.4. Network Intrusion Detection and Prevention . . . . . . . 10
6.5. Firewalling . . . . . . . . . . . . . . . . . . . . . . . 10 6.5. Firewalling . . . . . . . . . . . . . . . . . . . . . . . 10
7. Operational Implications . . . . . . . . . . . . . . . . . . 11 7. Operational Implications . . . . . . . . . . . . . . . . . . 11
7.1. Inability to Find Layer-4 Information . . . . . . . . . . 11 7.1. Inability to Find Layer-4 Information . . . . . . . . . . 11
7.2. Route-Processor Protection . . . . . . . . . . . . . . . 11 7.2. Route-Processor Protection . . . . . . . . . . . . . . . 11
7.3. Inability to Perform Fine-grained Filtering . . . . . . . 12 7.3. Inability to Perform Fine-grained Filtering . . . . . . . 12
7.4. Security Concerns Associated with IPv6 Extension Headers 12 7.4. Security Concerns Associated with IPv6 Extension Headers 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13 9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . 14 11.1. Normative References . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 15 11.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
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 may be middle-boxes, and evidence exists that IPv6 packets with EHs are
intentionally dropped in the public Internet in some network intentionally dropped in the public Internet in some network
deployments. deployments.
The authors of this document have been involved in numerous The authors of this document have been involved in numerous
discussions about IPv6 extension headers (both within the IETF and in discussions about IPv6 extension headers (both within the IETF and in
other fora), and have noticed that the security and operational other fora), and have noticed that the security and operational
implications associated with IPv6 EHs were unknown to the larger implications associated with IPv6 EHs were unknown to the larger
audience participating in these discussions. audience participating in these discussions.
This document has the following goals: This document has the following goals:
o Raise awareness about the operational and security implications of o Raise awareness about the operational and security implications of
IPv6 Extension Headers, and presents reasons why some networks may IPv6 Extension Headers specified in [RFC8200], and present reasons
intentionally drop packets containing IPv6 Extension Headers. why some networks resort to intentionally dropping packets
containing IPv6 Extension Headers.
o Highlight areas where current IPv6 support by networking devices o Highlight areas where current IPv6 support by networking devices
maybe sub-optimal, such that the aforementioned support is maybe sub-optimal, such that the aforementioned support is
improved. improved.
o Highlight operational issues associated with IPv6 extension o 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 3 provides background information about the IPv6 packet Section 3 provides background information about the IPv6 packet
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IPv6 extension headers. Section 5 discusses packet forwarding engine IPv6 extension headers. Section 5 discusses packet forwarding engine
constraints in contemporary routers. Section 6 discusses why constraints in contemporary routers. Section 6 discusses why
contemporary routers and middle-boxes may need to access Layer-4 contemporary routers and middle-boxes may need to access Layer-4
information to make a forwarding decision. Finally, Section 7 information to make a forwarding decision. Finally, Section 7
discusses the operational implications of IPv6 EHs. discusses the operational implications of IPv6 EHs.
2. Disclaimer 2. 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 may be 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 dropped. packets, but rather an analysis of why they are dropped.
3. Background Information 3. 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
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been discussed in IETF circles: been discussed in IETF circles:
o [I-D.taylor-v6ops-fragdrop] discusses a rationale for which o [I-D.taylor-v6ops-fragdrop] discusses a rationale for which
operators drop IPv6 fragments. operators drop IPv6 fragments.
o [I-D.wkumari-long-headers] discusses possible issues arising from o [I-D.wkumari-long-headers] discusses possible issues arising from
"long" IPv6 header chains. "long" IPv6 header chains.
o [I-D.kampanakis-6man-ipv6-eh-parsing] describes how o [I-D.kampanakis-6man-ipv6-eh-parsing] describes how
inconsistencies in the way IPv6 packets with extension headers are inconsistencies in the way IPv6 packets with extension headers are
parsed by different implementations may result in evasion of parsed by different implementations could result in evasion of
security controls, and presents guidelines for parsing IPv6 security controls, and presents guidelines for parsing IPv6
extension headers with the goal of providing a common and extension headers with the goal of providing a common and
consistent parsing methodology for IPv6 implementations. consistent parsing methodology for IPv6 implementations.
o [I-D.ietf-opsec-ipv6-eh-filtering] analyzes the security o [I-D.ietf-opsec-ipv6-eh-filtering] analyzes the security
implications of IPv6 EHs, and the operational implications of implications of IPv6 EHs, and the operational implications of
dropping packets that employ IPv6 EHs and associated options. dropping packets that employ IPv6 EHs and associated options.
o [RFC7113] discusses how some popular RA-Guard implementations are o [RFC7113] discusses how some popular RA-Guard implementations are
subject to evasion by means of IPv6 extension headers. subject to evasion by means of IPv6 extension headers.
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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 examine and process the Hop-by-Hop Options header" from [RFC2460], by
specifying that only nodes that have been explicitly configured to specifying that only nodes that have been explicitly configured to
process the Hop-by-Hop Options header are required to do so. 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], [Gont-IEPG88], [Gont-Chown-IEPG89], and o [PMTUD-Blackholes] and [Linkova-Gont-IEPG90] presented some
[Linkova-Gont-IEPG90] presented some preliminary measurements preliminary measurements regarding the extent to which packet
regarding the extent to which packet containing IPv6 EHs are containing IPv6 EHs are dropped in the public Internet.
dropped in the public Internet.
o [RFC7872] presents more comprehensive results and documents the o [RFC7872] presents more comprehensive results and documents the
methodology for obtaining the presented results. methodology for obtaining the presented results.
o [Huston-2017] and [Huston-2020] measured packet drops resulting o [Huston-2017] and [Huston-2020] measured packet drops resulting
from IPv6 fragmentation when communicating with DNS servers. from IPv6 fragmentation when communicating with DNS servers.
5. Packet Forwarding Engine Constraints 5. Packet Forwarding Engine Constraints
Most contemporary routers use dedicated hardware (e.g. ASICs or Most contemporary routers use dedicated hardware (e.g. ASICs or
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forwarding decision. 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 form to the control plane for more in-depth analysis, but this is
unfeasible on most current router architectures as a result of the unfeasible on most current router architectures as a result of the
vast difference between the hardware forwarding capacity of the vast difference between the hardware forwarding capacity of the
router and processing capacity of the control plane and the size of router and processing capacity of the control plane and the size of
the management link which connects the control plane to the the management link which connects the control plane to the
forwarding plane. forwarding plane.
If an IPv6 header chain is sufficiently long that its header exceeds If an IPv6 header chain is sufficiently long that it exceeds the
the packet look-up capacity of the router, then it may be dropped due packet look-up capacity of the router, the router could resort to
to hardware inability to determine how it should be handled. dropping the packet, as a result of being unable to determine how the
packet should be handled.
5.1. Recirculation 5.1. Recirculation
Although TLV chains are amenable to iterative processing on Although TLV chains are amenable to iterative processing on
architectures which have packet look-up engines with deep inspection architectures that have packet look-up engines with deep inspection
capabilities, some packet forwarding engines manage IPv6 Extension capabilities, some packet forwarding engines manage IPv6 Extension
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, as it allows arbitrarily long header limited look-up 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 look-up 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 may impact data-plane throughput performance forwarding engine, this could impact data-plane throughput
on the router. performance on the router.
6. Requirement to Process Layer-3/layer-4 information in Intermediate 6. Requirement to Process Layer-3/layer-4 information in Intermediate
Systems Systems
The following subsections discuss some of reasons for which The following subsections discuss some of the reasons for which
contemporary routers and middle-boxes may need to process Layer-3/ contemporary routers and middle-boxes may need to process Layer-3/
layer-4 information to make a forwarding decision. layer-4 information to make a forwarding decision.
6.1. ECMP and Hash-based Load-Sharing 6.1. ECMP and Hash-based Load-Sharing
In the case of ECMP (equal cost multi path) load sharing, the router In the case of ECMP (equal cost multi path) load sharing, the router
on the sending side of the link needs to make a decision regarding on the sending side of the link needs to make a decision regarding
which of the links to use for a given packet. Since round-robin which of the links to use for a given packet. Since round-robin
usage of the links is usually avoided in order to prevent packet usage of the links is usually avoided to prevent packet reordering,
reordering, forwarding engines need to use a mechanism which will forwarding engines need to use a mechanism that will consistently
consistently forward the same data streams down the same forwarding forward the same data streams down the same forwarding paths. Most
paths. Most forwarding engines achieve this by calculating a simple forwarding engines achieve this by calculating a simple hash using an
hash using an n-tuple gleaned from a combination of layer-2 through n-tuple gleaned from a combination of layer-2 through to layer-4
to layer-4 packet header information. This n-tuple will typically packet header information. This n-tuple will typically use the src/
use the src/dst MAC address, src/dst IP address, and if possible dst MAC address, src/dst IP address, and if possible further layer-4
further layer-4 src/dst port information. As layer-4 port src/dst port information. Layer-4 port information can increase the
information increases the entropy of the hash, it is normally highly entropy of the hash, and it is often thought desirable to use it if
desirable to use it where possible. available.
We note that in the IPv6 world, flows are expected to be identified We note that in the IPv6 world, flows are expected to be identified
by means of the IPv6 Flow Label [RFC6437]. Thus, ECMP and Hash-based by means of the IPv6 Flow Label [RFC6437]. Thus, ECMP and Hash-based
Load-Sharing would be possible without the need to process the entire Load-Sharing would 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. However, we note that for a long time many IPv6 flows. However, we note that for a long time many IPv6
implementations failed to set the Flow Label, and ECMP and Hash-based implementations failed to set the Flow Label, and ECMP and Hash-based
Load-Sharing devices also did not employ the Flow Label for Load-Sharing devices also did not employ the Flow Label for
performing their task. performing their task.
Clearly, widespread support of [RFC6437] would relieve middle-boxes Clearly, widespread support of [RFC6437] would relieve middle-boxes
from having to process the entire IPv6 header chain, making Flow from having to process the entire IPv6 header chain, making Flow
Label-based ECMP and Hash-based Load-Sharing [RFC6438] feasible. Label-based ECMP and Hash-based Load-Sharing [RFC6438] feasible.
While support of [RFC6437] is currently widespread for current While support of [RFC6437] is currently widespread for current
versions of all popular host implementations, there is still only versions of all popular host implementations, there is still only
marginal usage of the IPv6 Flow Label for ECMP and load balancing marginal usage of the IPv6 Flow Label for ECMP and load balancing
[Cunha-2020] -- possibly as a result of issues that have been found [Cunha-2020]. A contributing factor could be the issues that have
in host implementations and middle-boxes [Jaeggli-2018]. been found in host implementations and middle-boxes [Jaeggli-2018].
6.2. Enforcing infrastructure ACLs 6.2. Enforcing infrastructure ACLs
Generally speaking, infrastructure ACLs (iACLs) drop unwanted packets Generally speaking, infrastructure ACLs (iACLs) drop unwanted packets
destined to parts of a provider's infrastructure, because they are destined to parts of a provider's infrastructure, because they are
not operationally needed and can be used for attacks of different not operationally needed and can be used for attacks of different
sorts against router control planes. Some traffic needs to be sorts against router control planes. Some traffic needs to be
differentiated depending on layer-3 or layer-4 criteria to achieve a differentiated depending on layer-3 or layer-4 criteria to achieve a
useful balance of protection and functionality, for example: useful balance of protection and functionality, for example:
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The case of customer DDoS protection and edge-to-core customer The case of customer DDoS protection and edge-to-core customer
protection filters is similar in nature to the infrastructure ACL protection filters is similar in nature to the infrastructure ACL
protection. Similar to infrastructure ACL protection, layer-4 ACLs protection. Similar to infrastructure ACL protection, layer-4 ACLs
generally need to be applied as close to the edge of the network as generally need to be applied as close to the edge of the network as
possible, even though the intent is usually to protect the customer possible, even though the intent is usually to protect the customer
edge rather than the provider core. Application of layer-4 DDoS edge rather than the provider core. Application of layer-4 DDoS
protection to a network edge is often automated using Flowspec protection to a network edge is often automated using Flowspec
[RFC5575]. [RFC5575].
For example, a web site which normally only handled traffic on TCP For example, a web site that normally only handled 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 randomised source IP address, thereby
rendering traditional [RFC5635] source-based real-time black hole rendering traditional [RFC5635] source-based real-time black hole
mechanisms useless. In this situation, DDoS protection ACLs could be mechanisms useless. In this situation, DDoS protection ACLs could be
configured to block all UDP traffic at the network edge without configured to block all UDP traffic at the network edge without
impairing the web server functionality in any way. Thus, being able impairing the web server functionality in any way. Thus, being able
to block arbitrary protocols at the network edge can avoid DDoS- to block arbitrary protocols at the network edge can avoid DDoS-
related problems both in the provider network and on the customer related problems both in the provider network and on the customer
edge link. edge link.
6.4. Network Intrusion Detection and Prevention 6.4. 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 inspect application-
layer traffic (if possible), but at the bare minimum inspect layer-4 layer traffic (if possible), but at the bare minimum inspect layer-4
flows. When attack activity is inferred, the operator is signaled of flows. When attack activity is inferred, the operator is signaled of
the potential intrusion attempt. the potential intrusion attempt.
Network Intrusion Prevention Systems (IPS) operate similarly to Network Intrusion Prevention Systems (IPS) operate similarly to
NIDS's, but they may also prevent intrusions by reacting to detected NIDS's, 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 may result problematic for NIDS/IPS, since: Use of extension headers can result problematic for NIDS/IPS, since:
o Extension headers increase the complexity of resulting traffic, o Extension headers increase the complexity of resulting traffic,
and the associated work and system requirements to process it. and the associated work and system requirements to process it.
o Use of unknown extension headers may prevent an NIDS/IPS to o Use of unknown extension headers can prevent an NIDS/IPS to
process layer-4 information process layer-4 information
o Use of IPv6 fragmentation requires a stateful fragment-reassembly o 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 may be 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.
6.5. Firewalling 6.5. Firewalling
Firewalls enforce security policies by means of packet filtering. Firewalls enforce security policies by means of packet filtering.
These systems generally inspect layer-3 and layer-4 traffic, and may These systems generally inspect layer-3 and layer-4 traffic, and can
also examine application-layer traffic flows. often also examine application-layer traffic flows.
As with NIDS/IPS (Section 6.4), use of IPv6 extension headers may As with NIDS/IPS (Section 6.4), use of IPv6 extension headers can
represent a challenge to network firewalls, since: represent a challenge to network firewalls, since:
o Extension headers increase the complexity of resulting traffic, o Extension headers increase the complexity of resulting traffic,
and the associated work and system requirements to process it (see and the associated work and system requirements to process it (see
e.g. [Zack-FW-Benchmark]). e.g. [Zack-FW-Benchmark]).
o Use of unknown extension headers may prevent an NIDS/IPS to o Use of unknown extension headers can prevent firewalls to process
process layer-4 information layer-4 information
o Use of IPv6 fragmentation requires a stateful fragment-reassembly o 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, whether because of the challenges represented by As a result, whether because of the challenges represented by
extension headers or because the use of IPv6 extension headers has extension headers or because the use of IPv6 extension headers has
not been explicitly allowed, packets employing IPv6 extension headers not been explicitly allowed, packets employing IPv6 extension headers
may be dropped by network firewalls. are often dropped by network firewalls.
7. Operational Implications 7. Operational Implications
7.1. Inability to Find Layer-4 Information 7.1. Inability to Find Layer-4 Information
As discussed in Section 6, contemporary routers and middle-boxes that As discussed in Section 6, contemporary routers and middle-boxes that
need to find the layer-4 header must process the entire IPv6 need to find the layer-4 header must process the entire IPv6
extension header chain. When such devices are unable to obtain the extension header chain. When such devices are unable to obtain the
required information, they may simply resort to dropping the required information, the forwarding device has the option to drop
corresponding packets. the packet unconditionally, forward the packet unconditionally, or
process the packet outside the normal forwarding path. Forwarding
packets unconditionally will usually allow for the circumvention of
security controls (see e.g. Section 6.5), while processing packets
outside of the normal forwarding path will usually open the door to
DoS attacks (see e.g. Section 5). Thus, in these scenarios, devices
often simply resort to dropping such packets unconditionally.
7.2. Route-Processor Protection 7.2. Route-Processor Protection
Most contemporary routers have a fast hardware-assisted forwarding Most contemporary routers have a fast hardware-assisted forwarding
plane and a loosely coupled control plane, connected together with a plane and a loosely coupled control plane, connected together with a
link that has much less capacity than the forwarding plane could link that has much less capacity than the forwarding plane could
handle. Traffic differentiation cannot be done by the control plane handle. Traffic differentiation cannot be done by the control plane
side, because this would overload the internal link connecting the side, because this would overload the internal link connecting the
forwarding plane to the control plane. 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 since
in most circumstances, the corresponding packet is punted to the in most circumstances, the corresponding packet is punted to the
control plane for processing. As a result, operators usually drop control plane for processing. As a result, operators usually drop
IPv6 packets containing this extension header. Please see [RFC6192] IPv6 packets containing this extension header. Please see [RFC6192]
for advice regarding protection of the router control plane. for advice regarding protection of the router control plane.
7.3. Inability to Perform Fine-grained Filtering 7.3. Inability to Perform Fine-grained Filtering
Some router implementations lack fine-grained filtering of IPv6 Some router implementations do not have support for fine-grained
extension headers. For example, an operator may want to drop packets filtering of IPv6 extension headers. For example, an operator that
containing Routing Header Type 0 (RHT0) but may only be able to wishes to drop packets containing Routing Header Type 0 (RHT0), may
filter on the extension header type (Routing Header). As a result, only be able to filter on the extension header type (Routing Header).
the operator may end up enforcing a more coarse filtering policy This could result in an operator enforcing a more coarse filtering
(e.g. "drop all packets containing a Routing Header" vs. "only drop policy (e.g. "drop all packets containing a Routing Header" vs. "only
packets that contain a Routing Header Type 0"). drop packets that contain a Routing Header Type 0").
7.4. Security Concerns Associated with IPv6 Extension Headers 7.4. 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 o Evasion of security controls
o DoS due to processing requirements o DoS due to processing requirements
o DoS due to implementation errors o DoS due to implementation errors
o Extension Header-specific issues o Extension Header-specific issues
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" ("Internet Header Length") IPv4 header
field, the structure of IPv6 packets is more flexible and complex, field, the structure of IPv6 packets is more flexible and complex,
and may represent a challenge for devices that need to find this and can represent a challenge for devices that need to find this
information, since locating upper-layer protocol information requires information, since locating upper-layer protocol information requires
that all IPv6 extension headers be examined. This has presented that all IPv6 extension headers be examined. This has presented
implementation difficulties, and packet filtering mechanisms that implementation difficulties, and some packet filtering mechanisms
require upper-layer information (even if just the upper layer that require upper-layer information (even if just the upper layer
protocol type) can be trivially circumvented by inserting IPv6 protocol type) can be trivially circumvented by inserting IPv6
Extension Headers between the main IPv6 header and the upper layer Extension Headers between the main IPv6 header and the upper layer
protocol. [RFC7113] describes this issue for the RA-Guard case, but protocol. [RFC7113] describes this issue for the RA-Guard case, but
the same techniques can be employed to circumvent other IPv6 firewall the same techniques could be employed to circumvent other IPv6
and packet filtering mechanisms. Additionally, implementation firewall and packet filtering mechanisms. Additionally,
inconsistencies in packet forwarding engines may result in evasion of implementation inconsistencies in packet forwarding engines can
security controls [I-D.kampanakis-6man-ipv6-eh-parsing] [Atlasis2014] result in evasion of security controls
[BH-EU-2014]. [I-D.kampanakis-6man-ipv6-eh-parsing] [Atlasis2014] [BH-EU-2014].
Packets with attached IPv6 Extension Headers may impact performance Packets with attached IPv6 Extension Headers can impact performance
on routers that forward them. Unless appropriate mitigations are put on routers that forward them. Unless appropriate mitigations are put
in place (e.g., packet dropping and/or rate-limiting), an attacker in place (e.g., packet dropping and/or rate-limiting), an attacker
could simply send a large amount of IPv6 traffic employing IPv6 could simply send a large amount of IPv6 traffic employing IPv6
Extension Headers with the purpose of performing a Denial of Service Extension Headers with the purpose of performing a Denial of Service
(DoS) attack (see Section 7 for further details). (DoS) attack (see Section 7 for further details).
NOTE: NOTE:
In the most trivial case, a packet that includes a Hop-by-Hop In the most trivial case, a packet that includes a Hop-by-Hop
Options header might go through the slow forwarding path, and be Options header might go through the slow forwarding path, and be
processed by the router's CPU. Another possible case might be processed by the router's CPU. Another possible case might be
where a router that has been configured to enforce an ACL based on where a router that has been configured to enforce an ACL based on
upper-layer information (e.g., upper layer protocol or TCP upper-layer information (e.g., upper layer protocol or TCP
Destination Port), needs to process the entire IPv6 header chain Destination Port), needs to process the entire IPv6 header chain
(in order to find the required information), causing the packet to (in order to find the required information), causing the packet to
be processed in the slow path [Cisco-EH-Cons]. We note that, for be processed in the slow path [Cisco-EH-Cons]. We note that, for
obvious reasons, the aforementioned performance issues may affect obvious reasons, the aforementioned performance issues can affect
other devices such as firewalls, Network Intrusion Detection other devices such as firewalls, Network Intrusion Detection
Systems (NIDS), etc. [Zack-FW-Benchmark]. The extent to which Systems (NIDS), etc. [Zack-FW-Benchmark]. The extent to which
these devices are affected is typically implementation-dependent. these devices are affected is typically implementation-dependent.
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-Frag1], Header processing continue to be discovered (see e.g. [Cisco-Frag1],
[Cisco-Frag2], and [FreeBSD-SA]). Because there is currently little [Cisco-Frag2], and [FreeBSD-SA]). Because there is currently little
operational reliance on IPv6 Extension headers, the corresponding operational reliance on IPv6 Extension headers, the corresponding
skipping to change at page 13, line 49 skipping to change at page 14, line 8
9. Security Considerations 9. Security Considerations
The security implications of IPv6 extension headers are discussed in The security implications of IPv6 extension headers are discussed in
Section 7.4. This document does not introduce any new security Section 7.4. This document does not introduce any new security
issues. issues.
10. Acknowledgements 10. Acknowledgements
The authors would like to thank (in alphabetical order) Mikael The authors would like to thank (in alphabetical order) Mikael
Abrahamsson, Fred Baker, Brian Carpenter, Tim Chown, Owen DeLong, Tom Abrahamsson, Fred Baker, Dale W. Carder, Brian Carpenter, Tim Chown,
Herbert, Lee Howard, Tom Petch, Sander Steffann, Eduard Vasilenko, Owen DeLong, Gorry Fairhurst, Tom Herbert, Lee Howard, Tom Petch,
Eric Vyncke, Jingrong Xie, and Andrew Yourtchenko, for providing Sander Steffann, Eduard Vasilenko, Eric Vyncke, Jingrong Xie, and
valuable comments on earlier versions of this document. Andrew Yourtchenko, for providing valuable comments on earlier
versions of this document.
Fernando Gont would like to thank Jan Zorz / Go6 Lab Fernando Gont would like to thank Jan Zorz / Go6 Lab
<https://go6lab.si/>, Jared Mauch, and Sander Steffann <https://go6lab.si/>, Jared Mauch, and Sander Steffann
<https://steffann.nl/>, for providing access to systems and networks <https://steffann.nl/>, for providing access to systems and networks
that were employed to perform experiments and measurements involving that were employed to perform experiments and measurements involving
packets with IPv6 Extension Headers. packets with IPv6 Extension Headers.
11. References 11. References
11.1. Normative References 11.1. Normative References
skipping to change at page 16, line 23 skipping to change at page 16, line 29
routes", NPS/CAIDA 2020 Virtual IPv6 Workshop, 2020, routes", NPS/CAIDA 2020 Virtual IPv6 Workshop, 2020,
<https://www.cmand.org/workshops/202006-v6/slides/ <https://www.cmand.org/workshops/202006-v6/slides/
cunha.pdf>. cunha.pdf>.
[FreeBSD-SA] [FreeBSD-SA]
FreeBSD, "FreeBSD Security Advisory FreeBSD-SA-20:24.ipv6: FreeBSD, "FreeBSD Security Advisory FreeBSD-SA-20:24.ipv6:
IPv6 Hop-by-Hop options use-after-free bug", September IPv6 Hop-by-Hop options use-after-free bug", September
2020, <https://www.freebsd.org/security/advisories/ 2020, <https://www.freebsd.org/security/advisories/
FreeBSD-SA-20:24.ipv6.asc>. FreeBSD-SA-20:24.ipv6.asc>.
[Gont-Chown-IEPG89]
Gont, F. and T. Chown, "A Small Update on the Use of IPv6
Extension Headers", IEPG 89. London, UK. March 2, 2014,
<http://www.iepg.org/2014-03-02-ietf89/fgont-iepg-ietf89-
eh-update.pdf>.
[Gont-IEPG88]
Gont, F., "Fragmentation and Extension header Support in
the IPv6 Internet", IEPG 88. Vancouver, BC, Canada.
November 13, 2013, <http://www.iepg.org/2013-11-ietf88/
fgont-iepg-ietf88-ipv6-frag-and-eh.pdf>.
[Huston-2017] [Huston-2017]
Huston, G., "Dealing with IPv6 fragmentation in the Huston, G., "Dealing with IPv6 fragmentation in the
DNS", APNIC Blog, 2017, DNS", APNIC Blog, 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, 2020,
<https://www.cmand.org/workshops/202006-v6/ <https://www.cmand.org/workshops/202006-v6/
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