Operational Implications of IPv6 Packets with Extension Headers
draft-ietf-v6ops-ipv6-ehs-packet-drops-08
| Document | Type | Active Internet-Draft (v6ops WG) | ||
|---|---|---|---|---|
| Authors | Fernando Gont , Nick Hilliard , Gert Doering , Warren Kumari , Geoff Huston , Will LIU | |||
| Last updated | 2021-07-21 (latest revision 2021-06-11) | |||
| Replaces | draft-gont-v6ops-ipv6-ehs-packet-drops | |||
| Stream | Internet Engineering Task Force (IETF) | |||
| Intended RFC status | Informational | |||
| Formats | pdf htmlized bibtex | |||
| Reviews | ||||
| Stream | WG state | Submitted to IESG for Publication | ||
| Document shepherd | Ron Bonica | |||
| Shepherd write-up | Show (last changed 2021-01-07) | |||
| IESG | IESG state | RFC Ed Queue | ||
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(None)
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| Consensus Boilerplate | Yes | |||
| Telechat date | ||||
| Responsible AD | Robert Wilton | |||
| Send notices to | rbonica@juniper.net | |||
| IANA | IANA review state | IANA OK - No Actions Needed | ||
| IANA action state | No IANA Actions | |||
| RFC Editor | RFC Editor state | AUTH48 | ||
| Details | ||||
IPv6 Operations Working Group (v6ops) F. Gont
Internet-Draft SI6 Networks
Intended status: Informational N. Hilliard
Expires: December 13, 2021 INEX
G. Doering
SpaceNet AG
W. Kumari
Google
G. Huston
APNIC
W. Liu
Huawei Technologies
June 11, 2021
Operational Implications of IPv6 Packets with Extension Headers
draft-ietf-v6ops-ipv6-ehs-packet-drops-08
Abstract
This document summarizes the operational implications of IPv6
extension headers specified in the IPv6 protocol specification
(RFC8200), and attempts to analyze reasons why packets with IPv6
extension headers are often dropped in the public Internet.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 13, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Background Information . . . . . . . . . . . . . . . . . . . 3
5. Previous Work on IPv6 Extension Headers . . . . . . . . . . . 5
6. Packet Forwarding Engine Constraints . . . . . . . . . . . . 7
6.1. Recirculation . . . . . . . . . . . . . . . . . . . . . . 8
7. Requirement to Process Layer-3/layer-4 information in
Intermediate Systems . . . . . . . . . . . . . . . . . . . . 8
7.1. ECMP and Hash-based Load-Sharing . . . . . . . . . . . . 8
7.2. Enforcing infrastructure ACLs . . . . . . . . . . . . . . 9
7.3. DDoS Management and Customer Requests for Filtering . . . 10
7.4. Network Intrusion Detection and Prevention . . . . . . . 10
7.5. Firewalling . . . . . . . . . . . . . . . . . . . . . . . 11
8. Operational and Security Implications . . . . . . . . . . . . 12
8.1. Inability to Find Layer-4 Information . . . . . . . . . . 12
8.2. Route-Processor Protection . . . . . . . . . . . . . . . 12
8.3. Inability to Perform Fine-grained Filtering . . . . . . . 12
8.4. Security Concerns Associated with IPv6 Extension Headers 12
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
10. Security Considerations . . . . . . . . . . . . . . . . . . . 14
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . 14
12.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
IPv6 Extension Headers (EHs) allow for the extension of the IPv6
protocol, and provide support for core functionality such as IPv6
fragmentation. However, common implementation limitations suggest
that EHs present a challenge for IPv6 packet routing equipment and
middle-boxes, and evidence exists that IPv6 packets with EHs are
intentionally dropped in the public Internet in some circumstances.
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This document has the following goals:
o Raise awareness about the operational and security implications of
IPv6 Extension Headers specified in [RFC8200], and present reasons
why some networks resort to intentionally dropping packets
containing IPv6 Extension Headers.
o Highlight areas where current IPv6 support by networking devices
maybe sub-optimal, such that the aforementioned support is
improved.
o Highlight operational issues associated with IPv6 extension
headers, such that those issues are considered in IETF
standardization efforts.
Section 4 provides background information about the IPv6 packet
structure and associated implications. Section 5 of this document
summarizes the previous work that has been carried out in the area of
IPv6 extension headers. Section 6 discusses packet forwarding engine
constraints in contemporary routers. Section 7 discusses why
intermediate systems may need to access Layer-4 information to make a
forwarding decision. Finally, Section 8 discusses the operational
implications of IPv6 EHs.
2. Terminology
This document uses the term "intermediate system" to describe both
routers and middle-boxes, when there is no need to distinguish
between the two and where the important issue is that the device
being discussed forwards packets.
3. Disclaimer
This document analyzes the operational challenges represented by
packets that employ IPv6 Extension Headers, and documents some of the
operational reasons why these packets are often dropped in the public
Internet. This document is not a recommendation to drop such
packets, but rather an analysis of why they are currently dropped.
4. Background Information
It is useful to compare the basic structure of IPv6 packets against
that of IPv4 packets, and analyze the implications of the two
different packet structures.
IPv4 packets have a variable-length header size, that allows for the
use of IPv4 "options" -- optional information that may be of use by
nodes processing IPv4 packets. The IPv4 header length is specified
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in the IHL header field of the mandatory IPv4 header, and must be in
the range from 20 octets (the minimum IPv4 header size) to 60 octets
(accommodating at most 40 octets of options). The upper-layer
protocol type is specified via the "Protocol" field of the mandatory
IPv4 header.
Protocol, IHL
+--------+
| |
| v
+------//-----+------------------------+
| | |
| IPv4 | Upper-Layer |
| Header | Protocol |
| | |
+-----//------+------------------------+
variable length
<------------->
Figure 1: IPv4 Packet Structure
IPv6 took a different approach to the IPv6 packet structure. Rather
than employing a variable-length header as IPv4 does, IPv6 employs a
linked-list-like packet structure, where a mandatory fixed-length
IPv6 header is followed by an arbitrary number of optional extension
headers, with the upper-layer header being the last header in the
IPv6 header chain. Each extension header typically specifies its
length (unless it is implicit from the extension header type), and
the "next header" type that follows in the IPv6 header chain.
NH NH, EH-length NH, EH-length
+-------+ +------+ +-------+
| | | | | |
| v | v | v
+-------------+-------------+-//-+---------------+--------------+
| | | | | |
| IPv6 | Ext. | | Ext. | Upper-Layer |
| header | Header | | Header | Protocol |
| | | | | |
+-------------+-------------+-//-+---------------+--------------+
fixed length variable number of EHs & length
<------------> <-------------------------------->
Figure 2: IPv6 Packet Structure
This packet structure has the following implications:
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o [RFC8200] requires the entire IPv6 header chain to be contained in
the first fragment of a packet, therefore limiting the IPv6
extension header chain to the size of the path MTU.
o Other than the path MTU constraints, there are no other limits to
the number of IPv6 EHs that may be present in a packet.
Therefore, there is no upper-limit regarding "how deep into the
IPv6 packet" the upper-layer may be found.
o 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
entire IPv6 header chain, in sequence, starting from the mandatory
IPv6 header, until the last header in the IPv6 header chain is
found.
5. Previous Work on IPv6 Extension Headers
Some of the operational and security implications of IPv6 Extension
Headers have been discussed at the IETF:
o [I-D.taylor-v6ops-fragdrop] discusses a rationale for which
operators drop IPv6 fragments.
o [I-D.wkumari-long-headers] discusses possible issues arising from
"long" IPv6 header chains.
o [I-D.kampanakis-6man-ipv6-eh-parsing] describes how
inconsistencies in the way IPv6 packets with extension headers are
parsed by different implementations could result in evasion of
security controls, and presents guidelines for parsing IPv6
extension headers with the goal of providing a common and
consistent parsing methodology for IPv6 implementations.
o [I-D.ietf-opsec-ipv6-eh-filtering] analyzes the security
implications of IPv6 EHs, and the operational implications of
dropping packets that employ IPv6 EHs and associated options.
o [RFC7113] discusses how some popular RA-Guard implementations are
subject to evasion by means of IPv6 extension headers.
o [RFC8900] analyzes the fragility introduced by IP fragmentation.
A number of recent RFCs have discussed issues related to IPv6
extension headers, specifying updates to a previous revision of the
IPv6 standard [RFC2460], many of which have now been incorporated
into the current IPv6 core standard [RFC8200] or the IPv6 Node
Requirements [RFC8504]. Namely,
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o [RFC5095] discusses the security implications of Routing Header
Type 0 (RTH0), and deprecates it.
o [RFC5722] analyzes the security implications of overlapping
fragments, and provides recommendations in this area.
o [RFC7045] clarifies how intermediate nodes should deal with IPv6
extension headers.
o [RFC7112] discusses the issues arising in a specific fragmentation
case where the IPv6 header chain is fragmented into two or more
fragments (and formally forbids such fragmentation).
o [RFC6946] discusses a flawed (but common) processing of the so-
called IPv6 "atomic fragments", and specified improved processing
of such packets.
o [RFC8021] deprecates the generation of IPv6 atomic fragments.
o [RFC8504] clarifies processing rules for packets with extension
headers, and also allows hosts to enforce limits on the number of
options included in IPv6 EHs.
o [RFC7739] discusses the security implications of predictable
fragment Identification values, and provides recommendations for
the generation of these values.
o [RFC6980] analyzes the security implications of employing IPv6
fragmentation with Neighbor Discovery for IPv6, and formally
recommends against such usage.
Additionally, [RFC8200] has relaxed the requirement that "all nodes
examine and process the Hop-by-Hop Options header" from [RFC2460], by
specifying that only nodes that have been explicitly 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
employing IPv6 extension headers are dropped in the public Internet:
o [PMTUD-Blackholes] and [Linkova-Gont-IEPG90] presented some
preliminary measurements regarding the extent to which packet
containing IPv6 EHs are dropped in the public Internet.
o [RFC7872] presents more comprehensive results and documents the
methodology used to obtain these results.
o [Huston-2017] and [Huston-2020] measured packet drops resulting
from IPv6 fragmentation when communicating with DNS servers.
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6. Packet Forwarding Engine Constraints
Most contemporary carrier-grade routers use dedicated hardware, e.g.
application-specific integrated circuits (ASICs) or network
processing units (NPUs), to determine how to forward packets across
their internal fabrics (see [IEPG94-Scudder] and [APNIC-Scudder] for
details). One of the common methods of handling next-hop lookup is
to send a small portion of the ingress packet to a lookup engine with
specialised hardware, e.g. ternary content-addressable memory (TCAM)
or reduced latency dynamic random-access memory (RLDRAM), to
determine the packet's next-hop. Technical constraints mean that
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.
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
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
able to inspect far enough into a packet to determine how it should
be handled.
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
bytes of header.
If a hardware forwarding engine on a contemporary router cannot make
a forwarding decision about a packet because critical information is
not sent to the look-up engine, then the router will normally drop
the packet. Section 7 discusses some of the reasons for which a
contemporary router might need to access layer-4 information to make
a forwarding decision.
Historically, some packet forwarding engines punted packets of this
form to the control plane for more in-depth analysis, but this is
unfeasible on most contemporary router architectures as a result of
the vast difference between the hardware forwarding capacity of the
router and processing capacity of the control plane and the size of
the management link which connects the control plane to the
forwarding plane. Other platforms may have a separate software
forwarding plane that is distinct both from the hardware forwarding
plane and the control plane. However, the limited CPU resources of
this software-based forwarding plane, as well as the limited
bandwidth of the associated link results in similar throughput
constraints.
If an IPv6 header chain is sufficiently long that it exceeds the
packet look-up capacity of the router, the router might be unable to
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determine how the packet should be handled, and thus could resort to
dropping the packet.
6.1. Recirculation
Although TLV chains are amenable to iterative processing on
architectures that have packet look-up engines with deep inspection
capabilities, some packet forwarding engines manage IPv6 Extension
Header chains using recirculation. This approach processes Extension
Headers one at a time: when processing on one Extension Header is
completed, the packet is looped back through the processing engine
again. This recirculation process continues repeatedly until there
are no more Extension Headers left to be processed.
Recirculation is typically used on packet forwarding engines with
limited look-up capability, because it allows arbitrarily long header
chains to be processed without the complexity and cost associated
with packet forwarding engines which have deep look-up capabilities.
However, recirculation can impact the forwarding capacity of
hardware, as each packet will pass through the processing engine
multiple times. Depending on configuration, the type of packets
being processed, and the hardware capabilities of the packet
forwarding engine, this could impact data-plane throughput
performance on the router.
7. Requirement to Process Layer-3/layer-4 information in Intermediate
Systems
The following subsections discuss some of the reasons for which
intermediate systems may need to process Layer-3/layer-4 information
to make a forwarding decision.
7.1. ECMP and Hash-based Load-Sharing
In the case of equal cost multi-path (ECMP) load sharing, the
intermediate system needs to make a decision regarding which of its
interfaces to use to forward a given packet. Since round-robin usage
of the links is usually avoided to prevent packet reordering,
forwarding engines need to use a mechanism that will consistently
forward the same data streams down the same forwarding paths. Most
forwarding engines achieve this by calculating a simple hash using an
n-tuple gleaned from a combination of layer-2 through to layer-4
packet header information. This n-tuple will typically use the src/
dst MAC address, src/dst IP address, and if possible further layer-4
src/dst port information.
In the IPv6 world, flows are expected to be identified by means of
the IPv6 Flow Label [RFC6437]. Thus, ECMP and Hash-based Load-
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Sharing should be possible without the need to process the entire
IPv6 header chain to obtain upper-layer information to identify
flows. [RFC7098] discusses how the IPv6 Flow Label can used to
enhance layer 3/4 load distribution and balancing for large server
farms.
Historically, many IPv6 implementations failed to set the Flow Label,
and hash-based ECMP/load-sharing devices also did not employ the Flow
Label for performing their task. While support of [RFC6437] is
currently widespread for current versions of all popular host
implementations, there is still only marginal usage of the IPv6 Flow
Label for ECMP and load balancing [Cunha-2020]. A contributing
factor could be the issues that have been found in host
implementations and middle-boxes [Jaeggli-2018].
Clearly, widespread support of [RFC6437] would relieve intermediate
systems from having to process the entire IPv6 header chain, making
Flow Label-based ECMP and Load-Sharing [RFC6438] feasible.
If an intermediate system cannot determine consistent n-tuples for
calculating flow hashes, data streams are more likely to end up being
distributed unequally across ECMP and load-shared links. This may
lead to packet drops or reduced performance.
7.2. Enforcing infrastructure ACLs
Infrastructure ACLs (iACLs) drop unwanted packets destined to a
network's infrastructure. Typically, iACLs are deployed because
external direct access to a network's infrastructure addresses is
operationally unnecessary, and can be used for attacks of different
sorts against router control planes. To this end, traffic usually
needs to be differentiated on the basis of layer-3 or layer-4
criteria to achieve a useful balance of protection and functionality.
For example, an infrastructure may be configured with the following
policy:
o Permit some amount of ICMP echo (ping) traffic towards a router's
addresses for troubleshooting.
o Permit BGP sessions on the shared network of an exchange point
(potentially differentiating between the amount of packets/seconds
permitted for established sessions and connection establishment),
but do not permit other traffic from the same peer IP addresses.
If a forwarding router cannot determine consistent n-tuples for
calculating flow hashes, data streams are more likely to end up being
distributed unequally across ECMP and load-shared links. This may
lead to packet drops or reduced performance.
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If a network cannot deploy infrastructure ACLs, then the security of
the network may be compromised due to having more potential attack
vectors open.
7.3. DDoS Management and Customer Requests for Filtering
The case of customer DDoS protection and edge-to-core customer
protection filters is similar in nature to the iACL protection.
Similar to iACL protection, layer-4 ACLs 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 edge rather than the
provider core. Application of layer-4 DDoS protection to a network
edge is often automated using Flowspec [RFC8955] [RFC8956].
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
NTP and DNS packets with randomised source IP address, thereby
rendering traditional [RFC5635] source-based real-time black hole
mechanisms useless. In this situation, DDoS protection ACLs could be
configured to block all UDP traffic at the network edge without
impairing the web server functionality in any way. Thus, being able
to block arbitrary protocols at the network edge can avoid DDoS-
related problems both in the provider network and on the customer
edge link.
7.4. Network Intrusion Detection and Prevention
Network Intrusion Detection Systems (NIDS) examine network traffic
and try to identify traffic patterns that can be correlated to
network-based attacks. These systems generally inspect application-
layer traffic (if possible), but at the bare minimum inspect layer-4
flows. When attack activity is inferred, the operator is notified of
the potential intrusion attempt.
Network Intrusion Prevention Systems (IPS) operate similarly to
NIDS's, but they can also prevent intrusions by reacting to detected
attack attempts by e.g., triggering packet filtering policies at
firewalls and other devices.
Use of extension headers can be problematic for NIDS/IPS, since:
o Extension headers increase the complexity of resulting traffic,
and the associated work and system requirements to process it.
o Use of unknown extension headers can prevent an NIDS/IPS from
processing layer-4 information.
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o Use of IPv6 fragmentation requires a stateful fragment-reassembly
operation, even for decoy traffic employing forged source
addresses (see e.g., [nmap]).
As a result, in order to increase the efficiency or effectiveness of
these systems, packets employing IPv6 extension headers are often
dropped at the network ingress point(s) of networks that deploy these
systems.
7.5. Firewalling
Firewalls enforce security policies by means of packet filtering.
These systems usually inspect layer-3 and layer-4 traffic, but can
often also examine application-layer traffic flows.
As with NIDS/IPS (Section 7.4), use of IPv6 extension headers can
represent a challenge to network firewalls, since:
o Extension headers increase the complexity of resulting traffic,
and the associated work and system requirements to process it, as
outlined in [Zack-FW-Benchmark].
o Use of unknown extension headers can prevent firewalls from
processing layer-4 information.
o Use of IPv6 fragmentation requires a stateful fragment-reassembly
operation, even for decoy traffic employing forged source
addresses (see e.g., [nmap]).
Additionally, a common firewall filtering policy is the so-called
"default deny", where all traffic is blocked (by default), and only
expected traffic is added to an "allow/accept list".
As a result, packets employing IPv6 extension headers are often
dropped by network firewalls, either because of the challenges
represented by extension headers or because the use of IPv6 extension
headers has not been explicitly allowed.
Note that although the data presented in [Zack-FW-Benchmark] were
several years old at the time of publication of this document, many
contemporary firewalls use comparable hardware and software
architecture, and consequently the conclusions of this benchmark are
still relevant, despite its age.
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8. Operational and Security Implications
8.1. Inability to Find Layer-4 Information
As discussed in Section 7, intermediate systems that need to find the
layer-4 header must process the entire IPv6 extension header chain.
When such devices are unable to obtain the required information, the
forwarding device has the option to drop 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 7.5), while processing packets outside of the normal
forwarding path will usually open the door to DoS attacks (see e.g.,
Section 6). Thus, in these scenarios, devices often simply resort to
dropping such packets unconditionally.
8.2. Route-Processor Protection
Most contemporary carrier-grade routers have a fast hardware-assisted
forwarding plane and a loosely coupled control plane, connected
together with a link that has much less capacity than the forwarding
plane could handle. Traffic differentiation cannot be performed by
the control plane, because this would overload the internal link
connecting the forwarding plane to the control plane.
The Hop-by-Hop Options header has been particularly challenging since
in most circumstances, the corresponding packet is punted to the
control plane for processing. As a result, many operators drop IPv6
packets containing this extension header [RFC7872]. [RFC6192]
provides advice regarding protection of a router's control plane.
8.3. Inability to Perform Fine-grained Filtering
Some intermediate systems do not have support for fine-grained
filtering of IPv6 extension headers. For example, an operator that
wishes to drop packets containing Routing Header Type 0 (RHT0), may
only be able to filter on the extension header type (Routing Header).
This could result in an operator enforcing a more coarse filtering
policy (e.g., "drop all packets containing a Routing Header" vs.
"only drop packets that contain a Routing Header Type 0").
8.4. Security Concerns Associated with IPv6 Extension Headers
The security implications of IPv6 Extension Headers generally fall
into one or more of these categories:
o Evasion of security controls
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o DoS due to processing requirements
o DoS due to implementation errors
o Extension Header-specific issues
Unlike IPv4 packets where the upper-layer protocol can be trivially
found by means of the "IHL" ("Internet Header Length") IPv4 header
field, the structure of IPv6 packets is more flexible and complex.
This can represent a challenge for devices that need to find this
information, since locating upper-layer protocol information requires
that all IPv6 extension headers be examined. In turn, this presents
implementation difficulties, since some packet filtering mechanisms
that require upper-layer information (even if just the upper layer
protocol type) can be trivially circumvented by inserting IPv6
Extension Headers between the main IPv6 header and the upper layer
protocol. [RFC7113] describes this issue for the RA-Guard case, but
the same techniques could be employed to circumvent other IPv6
firewall and packet filtering mechanisms. Additionally,
implementation inconsistencies in packet forwarding engines can
result in evasion of security controls
[I-D.kampanakis-6man-ipv6-eh-parsing] [Atlasis2014] [BH-EU-2014].
Sometimes packets with IPv6 Extension Headers can impact throughput
performance on intermediate systems. Unless appropriate mitigations
are put in place (e.g., packet dropping and/or rate-limiting), an
attacker could simply send a large amount of IPv6 traffic employing
IPv6 Extension Headers with the purpose of performing a Denial of
Service (DoS) attack (see Section 6.1 and Section 8 for further
details).
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
processed by the router's CPU. Alternatively, a router configured
to enforce an ACL based on upper-layer information (e.g., upper
layer protocol or TCP Destination Port) may need to process the
entire IPv6 header chain in order to find the required
information, thereby causing the packet to be processed in the
slow path [Cisco-EH-Cons]. We note that, for obvious reasons, the
aforementioned performance issues can affect other devices such as
firewalls, Network Intrusion Detection Systems (NIDS), etc.
[Zack-FW-Benchmark]. The extent to which performance is affected
on these devices is implementation-dependent.
IPv6 implementations, like all other software, tend to mature with
time and wide-scale deployment. While the IPv6 protocol itself has
existed for over 20 years, serious bugs related to IPv6 Extension
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Header processing continue to be discovered (see e.g., [Cisco-Frag],
[Microsoft-SA], and [FreeBSD-SA]). Because there is currently little
operational reliance on IPv6 Extension headers, the corresponding
code paths are rarely exercised, and there is the potential for bugs
that still remain to be discovered in some implementations.
IPv6 Fragment Headers are employed to allow fragmentation of IPv6
packets. While many of the security implications of the
fragmentation / reassembly mechanism are known from the IPv4 world,
several related issues have crept into IPv6 implementations. These
range from denial of service attacks to information leakage, as
discussed in [RFC7739], [Bonica-NANOG58] and [Atlasis2012]).
9. IANA Considerations
This document has no IANA actions.
10. Security Considerations
The security implications of IPv6 extension headers are discussed in
Section 8.4. This document does not introduce any new security
issues.
11. 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, 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
[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
of Type 0 Routing Headers in IPv6", RFC 5095,
DOI 10.17487/RFC5095, December 2007,
<https://www.rfc-editor.org/info/rfc5095>.
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[RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments",
RFC 5722, DOI 10.17487/RFC5722, December 2009,
<https://www.rfc-editor.org/info/rfc5722>.
[RFC6946] Gont, F., "Processing of IPv6 "Atomic" Fragments",
RFC 6946, DOI 10.17487/RFC6946, May 2013,
<https://www.rfc-editor.org/info/rfc6946>.
[RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
with IPv6 Neighbor Discovery", RFC 6980,
DOI 10.17487/RFC6980, August 2013,
<https://www.rfc-editor.org/info/rfc6980>.
[RFC7112] Gont, F., Manral, V., and R. Bonica, "Implications of
Oversized IPv6 Header Chains", RFC 7112,
DOI 10.17487/RFC7112, January 2014,
<https://www.rfc-editor.org/info/rfc7112>.
[RFC8021] Gont, F., Liu, W., and T. Anderson, "Generation of IPv6
Atomic Fragments Considered Harmful", RFC 8021,
DOI 10.17487/RFC8021, January 2017,
<https://www.rfc-editor.org/info/rfc8021>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
January 2019, <https://www.rfc-editor.org/info/rfc8504>.
12.2. Informative References
[APNIC-Scudder]
Scudder, J., "Modern router architecture and IPv6", APNIC
Blog, June 4, 2020, <https://blog.apnic.net/2020/06/04/
modern-router-architecture-and-ipv6/>.
[Atlasis2012]
Atlasis, A., "Attacking IPv6 Implementation Using
Fragmentation", BlackHat Europe 2012. Amsterdam,
Netherlands. March 14-16, 2012,
<https://media.blackhat.com/bh-eu-12/Atlasis/bh-eu-12-
Atlasis-Attacking_IPv6-Slides.pdf>.
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[Atlasis2014]
Atlasis, A., "A Novel Way of Abusing IPv6 Extension
Headers to Evade IPv6 Security Devices", May 2014,
<http://www.insinuator.net/2014/05/a-novel-way-of-abusing-
ipv6-extension-headers-to-evade-ipv6-security-devices/>.
[BH-EU-2014]
Atlasis, A., Rey, E., and R. Schaefer, "Evasion of High-
End IDPS Devices at the IPv6 Era", BlackHat Europe 2014,
2014, <https://www.ernw.de/download/eu-14-Atlasis-Rey-
Schaefer-briefings-Evasion-of-HighEnd-IPS-Devices-wp.pdf>.
[Bonica-NANOG58]
Bonica, R., "IPV6 FRAGMENTATION: The Case For
Deprecation", NANOG 58. New Orleans, Louisiana, USA. June
3-5, 2013, <https://www.nanog.org/sites/default/files/
mon.general.fragmentation.bonica.pdf>.
[Cisco-EH-Cons]
Cisco, "IPv6 Extension Headers Review and Considerations",
October 2006,
<http://www.cisco.com/en/US/technologies/tk648/tk872/
technologies_white_paper0900aecd8054d37d.pdf>.
[Cisco-Frag]
Cisco, "Cisco IOS XR Software Crafted IPv6 Packet Denial
of Service Vulnerability", June 2015,
<http://tools.cisco.com/security/center/content/
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, "FreeBSD Security Advisory FreeBSD-SA-20:24.ipv6:
IPv6 Hop-by-Hop options use-after-free bug", September
2020, <https://www.freebsd.org/security/advisories/
FreeBSD-SA-20:24.ipv6.asc>.
[Huston-2017]
Huston, G., "Dealing with IPv6 fragmentation in the
DNS", APNIC Blog, 2017,
<https://blog.apnic.net/2017/08/22/dealing-ipv6-
fragmentation-dns/>.
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[Huston-2020]
Huston, G., "Measurement of IPv6 Extension Header
Support", NPS/CAIDA 2020 Virtual IPv6 Workshop, 2020,
<https://www.cmand.org/workshops/202006-v6/
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]
Petersen, B. and J. Scudder, "Modern Router Architecture
for Protocol Designers", IEPG 94. Yokohama, Japan.
November 1, 2015, <http://www.iepg.org/2015-11-01-ietf94/
IEPG-RouterArchitecture-jgs.pdf>.
[Jaeggli-2018]
Jaeggli, J., "IPv6 flow label: misuse in hashing", APNIC
Blog, 2018, <https://blog.apnic.net/2018/01/11/ipv6-flow-
label-misuse-hashing/>.
[Linkova-Gont-IEPG90]
Linkova, J. and F. Gont, "IPv6 Extension Headers in the
Real World v2.0", IEPG 90. Toronto, ON, Canada. July 20,
2014, <http://www.iepg.org/2014-07-20-ietf90/iepg-
ietf90-ipv6-ehs-in-the-real-world-v2.0.pdf>.
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[Microsoft-SA]
Microsoft, "Windows TCP/IP Remote Code Execution
Vulnerability (CVE-2021-24094)", February 2021,
<https://msrc.microsoft.com/update-guide/vulnerability/
CVE-2021-24094>.
[nmap] Fyodor, "Dealing with IPv6 fragmentation in the
DNS", Firewall/IDS Evasion and Spoofing,
<https://nmap.org/book/man-bypass-firewalls-ids.html>.
[PMTUD-Blackholes]
De Boer, M. and J. Bosma, "Discovering Path MTU black
holes on the Internet using RIPE Atlas", July 2012,
<http://www.nlnetlabs.nl/downloads/publications/pmtu-
black-holes-msc-thesis.pdf>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC5635] Kumari, W. and D. McPherson, "Remote Triggered Black Hole
Filtering with Unicast Reverse Path Forwarding (uRPF)",
RFC 5635, DOI 10.17487/RFC5635, August 2009,
<https://www.rfc-editor.org/info/rfc5635>.
[RFC6192] Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
Router Control Plane", RFC 6192, DOI 10.17487/RFC6192,
March 2011, <https://www.rfc-editor.org/info/rfc6192>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
of IPv6 Extension Headers", RFC 7045,
DOI 10.17487/RFC7045, December 2013,
<https://www.rfc-editor.org/info/rfc7045>.
[RFC7098] Carpenter, B., Jiang, S., and W. Tarreau, "Using the IPv6
Flow Label for Load Balancing in Server Farms", RFC 7098,
DOI 10.17487/RFC7098, January 2014,
<https://www.rfc-editor.org/info/rfc7098>.
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[RFC7113] Gont, F., "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", RFC 7113,
DOI 10.17487/RFC7113, February 2014,
<https://www.rfc-editor.org/info/rfc7113>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu,
"Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", RFC 7872,
DOI 10.17487/RFC7872, June 2016,
<https://www.rfc-editor.org/info/rfc7872>.
[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
and F. Gont, "IP Fragmentation Considered Fragile",
BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
<https://www.rfc-editor.org/info/rfc8900>.
[RFC8955] Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M.
Bacher, "Dissemination of Flow Specification Rules",
RFC 8955, DOI 10.17487/RFC8955, December 2020,
<https://www.rfc-editor.org/info/rfc8955>.
[RFC8956] Loibl, C., Ed., Raszuk, R., Ed., and S. Hares, Ed.,
"Dissemination of Flow Specification Rules for IPv6",
RFC 8956, DOI 10.17487/RFC8956, December 2020,
<https://www.rfc-editor.org/info/rfc8956>.
[Zack-FW-Benchmark]
Zack, E., "Firewall Security Assessment and Benchmarking
IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1,
Berlin, Germany. June 30, 2013,
<https://www.ipv6hackers.org/files/meetings/ipv6-hackers-
1/zack-ipv6hackers1-firewall-security-assessment-and-
benchmarking.pdf>.
Authors' Addresses
Fernando Gont
SI6 Networks
Segurola y Habana 4310, 7mo Piso
Villa Devoto, Ciudad Autonoma de Buenos Aires
Argentina
Email: fgont@si6networks.com
URI: https://www.si6networks.com
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Nick Hilliard
INEX
4027 Kingswood Road
Dublin 24
IE
Email: nick@inex.ie
Gert Doering
SpaceNet AG
Joseph-Dollinger-Bogen 14
Muenchen D-80807
Germany
Email: gert@space.net
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
Geoff Huston
Email: gih@apnic.net
URI: http://www.apnic.net
Will (Shucheng) Liu
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
P.R. China
Email: liushucheng@huawei.com
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