Internet Engineering Task Force (IETF) F. Gont

Internet Engineering Task Force (IETF) F. Gont
Request for Comments: 9288 SI6 Networks
Category: Informational W. Liu
ISSN: 2070-1721 Huawei Technologies
August 2022

Recommendations on the Filtering of IPv6 Packets Containing IPv6
Extension Headers at Transit Routers

Abstract

This document analyzes the security implications of IPv6 Extension
Headers and associated IPv6 options. Additionally, it discusses the
operational and interoperability implications of discarding packets
based on the IPv6 Extension Headers and IPv6 options they contain.
Finally, it provides advice on the filtering of such IPv6 packets at
transit routers for traffic not directed to them, for those cases
where such filtering is deemed as necessary.

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.

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/rfc9288.

Copyright Notice

Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.

Table of Contents

1. Introduction
2. Terminology and Assumptions Employed in This Document
2.1. Terminology
2.2. Applicability Statement
2.3. Router Default Behavior and Features
3. IPv6 Extension Headers
3.1. General Discussion
3.2. General Security Implications
3.3. Rationale for Our Advice on the Handling of IPv6 Packets
with Specific IPv6 Extension Headers
3.4. Summary of Advice on the Handling of IPv6 Packets with
Specific IPv6 Extension Headers
3.5. Advice on the Handling of IPv6 Packets with Specific IPv6
Extension Headers
3.6. Advice on the Handling of Packets with Unknown IPv6
Extension Headers
4. IPv6 Options
4.1. General Discussion
4.2. General Security Implications of IPv6 Options
4.3. Summary of Advice on the Handling of IPv6 Packets with
Specific IPv6 Options
4.4. Advice on the Handling of Packets with Specific IPv6
Options
4.5. Advice on the Handling of Packets with Unknown IPv6 Options
5. IANA Considerations
6. Privacy Considerations
7. Security Considerations
8. References
8.1. Normative References
8.2. Informative References
Acknowledgements
Authors' Addresses

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,
particularly when the IPv6 header chain needs to be processed for, as
an example, enforcing Access Control Lists (ACLs) or implementing
other functions [RFC9098].

Several studies (e.g., [Huston-2022], [JAMES], and [RFC7872]) suggest
that there is widespread dropping of IPv6 packets that contain IPv6
EHs. In some cases, such packet drops occur at transit routers.
While some operators are known to intentionally drop packets that
contain IPv6 EHs, it is possible that some of the measured packet
drops are the result of inappropriate advice in this area.

This document analyzes both the general security implications of IPv6
EHs, as well as the security implications of specific EH and option
types. It also provides advice on the filtering of IPv6 packets
based on the IPv6 EHs and the IPv6 options they contain. Since
various protocols may use IPv6 EHs (possibly with IPv6 options),
discarding packets based on the IPv6 EHs or IPv6 options they contain
can have implications on the proper functioning of such protocols.
Thus, this document also attempts to discuss the operational and
interoperability implications of such filtering policies.

The resulting packet filtering policy typically depends on where in
the network such policy is enforced. When the policy is enforced in
a transit network, the policy typically follows a "deny-list"
approach, where only packets with clear negative implications are
dropped. On the other hand, when the policy is enforced closer to
the destination systems, the policy typically follows an "accept-
list" approach, where only traffic that is expected to be received is
allowed. The advice in this document is aimed only at transit
routers that may need to enforce a filtering policy based on the IPv6
EHs and IPv6 options a packet may contain, following a "deny-list"
approach; hence, it is likely to be much more permissive than a
filtering policy to be employed at, for example, the edge of an
enterprise network. The advice in this document is meant to improve
the current situation of the dropping of packets with IPv6 EHs in the
Internet [RFC7872] in such cases where packets are being dropped due
to inappropriate or missing guidelines.

This document is similar in nature to [RFC7126], which addresses the
same problem for the IPv4 case. However, in IPv6, the problem space
is compounded by the fact that IPv6 specifies a number of IPv6 EHs
and a number of IPv6 options that may be valid only when included in
specific EH types.

This document completes and complements the considerations for
protecting the control plane from packets containing IP options that
can be found in [RFC6192].

Section 2 specifies the terminology and conventions employed
throughout this document. Section 3 discusses IPv6 EHs and provides
advice in the area of filtering IPv6 packets that contain such IPv6
EHs. Section 4 discusses IPv6 options and provides advice in the
area of filtering IPv6 packets that contain such options.

2. Terminology and Assumptions Employed in This Document

2.1. Terminology

The terms "permit" (allow the traffic), "drop" (drop with no
notification to sender), and "reject" (drop with appropriate
notification to sender) are employed as defined in [RFC3871].
Throughout this document, we also employ the term "discard" as a
generic term to indicate the act of discarding a packet, irrespective
of whether the sender is notified of such a drop and whether the
specific filtering action is logged.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

2.2. Applicability Statement

This document provides advice on the filtering of IPv6 packets with
EHs at transit routers for traffic not explicitly destined to them,
for cases in which such filtering is deemed as necessary.

2.3. Router Default Behavior and Features

This document assumes that nodes comply with the requirements in
[RFC7045]. Namely,

| If a forwarding node discards a packet containing a standard IPv6
| extension header, it MUST be the result of a configurable policy
| and not just the result of a failure to recognise such a header.
| This means that the discard policy for each standard type of
| extension header MUST be individually configurable. The default
| configuration SHOULD allow all standard extension headers.

The advice provided in this document is only meant to guide an
operator in configuring forwarding devices and is not to be
interpreted as advice regarding default configuration settings for
network devices. That is, this document provides advice with respect
to operational policies but does not change the implementation
defaults required by [RFC7045].

We recommend that configuration options be made available to govern
the processing of each IPv6 EH type and each IPv6 Option Type. Such
configuration options should include the following possible settings:

* Permit this IPv6 EH or IPv6 Option Type.

* Drop packets containing this IPv6 EH or IPv6 Option Type.

* Reject packets containing this IPv6 EH or IPv6 Option Type (where
the packet drop is signaled with an ICMPv6 error message).

* Rate-limit traffic containing this IPv6 EH or IPv6 Option Type.

* Ignore this IPv6 EH or IPv6 Option Type (as if it was not
present), and process the packet according the rules for the
remaining headers. We note that if a packet carries forwarding
information (e.g., in an IPv6 Routing Header (RH)), this might be
an inappropriate or undesirable action.

We note that special care needs to be taken when devices log packet
drops/rejects. Devices should count the number of packets dropped/
rejected, but the logging of drop/reject events should be limited so
as to not overburden device resources.

Finally, we note that when discarding packets, it is generally
desirable that the sender be signaled of the packet drop, since this
is of use for trouble-shooting purposes. However, throughout this
document (when recommending that packets be discarded), we
generically refer to the action as "discard" without specifying
whether the sender is signaled of the packet drop.

3. IPv6 Extension Headers

3.1. General Discussion

IPv6 EHs [RFC8200] allow for the extension of the IPv6 protocol.
Since both IPv6 EHs and upper-layer protocols share the same
namespace ("Next Header" registry/namespace), [RFC7045] identifies
which of the currently assigned Internet Protocol numbers identify
IPv6 EHs vs. upper-layer protocols. This document discusses the
filtering of packets based on the IPv6 EHs (as specified by
[RFC7045]) they contain.

[RFC8200] specifies that non-fragmented IPv6 datagrams and IPv6
First-Fragments must contain the entire IPv6 header chain [RFC7112].
Therefore, intermediate systems can enforce the filtering policies
discussed in this document or resort to simply discarding the
offending packets when they fail to include the entire IPv6 header
chain [RFC8200].

We note that in order to implement filtering rules on the fast path,
it may be necessary for the filtering device to limit the depth into
the packet that can be inspected before giving up. In circumstances
where such a limitation exists, it is recommended that
implementations provide a configuration option that specifies whether
to discard packets if the aforementioned limit is encountered.
Operators may then determine, according to their own circumstances,
how such packets will be handled.

3.2. General Security Implications

In some device architectures, IPv6 packets that contain IPv6 EHs can
cause the corresponding packets to be processed on the slow path and,
hence, may be leveraged for the purpose of Denial-of-Service (DoS)
attacks [RFC9098] [Cisco-EH] [FW-Benchmark].

Operators are urged to consider the IPv6 EH and IPv6 options handling
capabilities of their devices as they make deployment decisions in
the future.

3.3. Rationale for Our Advice on the Handling of IPv6 Packets with
Specific IPv6 Extension Headers

* IPv6 packets with IPv6 Extension Headers (or options) that are not
expected to traverse transit routers should be dropped.

* IPv6 packets with IPv6 Extension Headers (or options) that are
only expected to traverse transit routers when a specific
technology is employed should be permitted (or dropped) based on
the knowledge regarding the use of such technology in the transit
provider in question (i.e., permit the packets if the technology
is employed, or drop them).

* IPv6 packets with IPv6 Extension Headers (or options) that
represent a concrete attack vector to network infrastructure
devices should be dropped.

* IPv6 packets with any other IPv6 Extension Headers (or options)
should be permitted. This is an intentional trade-off made to
minimize ossification.

3.4. Summary of Advice on the Handling of IPv6 Packets with Specific
IPv6 Extension Headers

This section summarizes the advice provided in Section 3.5, providing
references to the specific sections in which a detailed analysis can
be found.

+=====================+=========================+===========+
| EH Type | Filtering Policy | Reference |
+=====================+=========================+===========+
| Hop-by-Hop Options | Drop or Ignore | Section |
| Header (Proto=0) | | 3.5.1 |
+---------------------+-------------------------+-----------+
| Routing Header | Drop only Routing Type | Section |
| (Proto=43) | 0, Routing Type 1, and | 3.5.2 |
| | Routing Type 3. Permit | |
| | other Routing Types | |
+---------------------+-------------------------+-----------+
| Fragment Header | Permit | Section |
| (Proto=44) | | 3.5.3 |
+---------------------+-------------------------+-----------+
| Encapsulating | Permit | Section |
| Security Payload | | 3.5.4 |
| (Proto=50) | | |
+---------------------+-------------------------+-----------+
| Authentication | Permit | Section |
| Header (Proto=51) | | 3.5.5 |
+---------------------+-------------------------+-----------+
| Destination Options | Permit | Section |
| Header(Proto=60) | | 3.5.6 |
+---------------------+-------------------------+-----------+
| Mobility Header | Permit | Section |
| (Proto=135) | | 3.5.7 |
+---------------------+-------------------------+-----------+
| Host Identity | Permit | Section |
| Protocol | | 3.5.8 |
| (Proto=139) | | |
+---------------------+-------------------------+-----------+
| Shim6 Protocol | Permit | Section |
| (Proto=140) | | 3.5.9 |
+---------------------+-------------------------+-----------+
| Use for | Drop | Section |
| experimentation and | | 3.5.10 |
| testing (Proto=253 | | |
| and 254) | | |
+---------------------+-------------------------+-----------+

Table 1: Summary of Advice on the Handling of IPv6
Packets with Specific IPv6 Extension Headers

3.5. Advice on the Handling of IPv6 Packets with Specific IPv6
Extension Headers

3.5.1. IPv6 Hop-by-Hop Options (Protocol Number=0)

3.5.1.1. Uses

The Hop-by-Hop (HBH) Options header is used to carry optional
information that may be examined by every node along a packet's
delivery path. It is expected that nodes will examine the Hop-by-Hop
Options header if explicitly configured to do so.

| NOTE: A previous revision of the IPv6 core specification
| [RFC2460] originally required all nodes to examine and process
| the Hop-by-Hop Options header. However, even before the
| publication of [RFC8200], a number of implementations already
| provided the option of ignoring this header unless explicitly
| configured to examine it.

3.5.1.2. Specification

This EH is specified in [RFC8200]. As of May 2022, the following
options have been specified for the Hop-by-Hop Options header:

* Type 0x00: Pad1 [RFC8200]

* Type 0x01: PadN [RFC8200]

* Type 0x05: Router Alert [RFC2711]

* Type 0x07: CALIPSO [RFC5570]

* Type 0x08: SMF_DPD [RFC6621]

* Type 0x23: RPL Option [RFC9008]

* Type 0x26: Quick-Start [RFC4782]

* Type 0x4D: (Deprecated)

* Type 0x63: RPL Option [RFC6553]

* Type 0x6D: MPL Option [RFC7731]

* Type 0x8A: Endpoint Identification (Deprecated) [NIMROD-EID]

* Type 0xC2: Jumbo Payload [RFC2675]

* Type 0xEE: IPv6 DFF Header [RFC6971]

* Type 0x1E: RFC3692-style Experiment [RFC4727]

* Type 0x3E: RFC3692-style Experiment [RFC4727]

* Type 0x5E: RFC3692-style Experiment [RFC4727]

* Type 0x7E: RFC3692-style Experiment [RFC4727]

* Type 0x9E: RFC3692-style Experiment [RFC4727]

* Type 0xBE: RFC3692-style Experiment [RFC4727]

* Type 0xDE: RFC3692-style Experiment [RFC4727]

* Type 0xFE: RFC3692-style Experiment [RFC4727]

3.5.1.3. Specific Security Implications

Legacy nodes that process this extension header might be subject to
DoS attacks.

| NOTE: While [RFC8200] has removed the requirement for all nodes
| to examine and process the Hop-by-Hop Options header, the
| deployed base may still reflect the legacy [RFC2460] behavior
| for a while; hence, the potential security problems of this EH
| are still of concern.

3.5.1.4. Operational and Interoperability Impact If Blocked

Discarding packets containing a Hop-by-Hop Options header would break
any of the protocols that rely on it for proper functioning. For
example, it would break RSVP [RFC2205] and multicast deployments and
would cause IPv6 jumbograms to be discarded.

3.5.1.5. Advice

Nodes implementing [RFC8200] would already ignore this extension
header unless explicitly required to process it. For legacy nodes
[RFC2460], the recommended configuration for the processing of these
packets depends on the features and capabilities of the underlying
platform, the configuration of the platform, and also the deployment
environment of the platform. On platforms that allow the forwarding
of packets with IPv6 HBH Options headers on the fast path, we
recommend that packets with IPv6 HBH Options headers be forwarded as
normal. Otherwise, on platforms in which the processing of packets
with IPv6 HBH Options headers is carried out in the slow path and an
option is provided to rate-limit these packets, we recommend that
this option be selected. Finally, when packets containing IPv6 HBH
Options headers are processed in the slow path and the underlying
platform does not have any mitigation options available for attacks
based on these packets, we recommend that such platforms discard
packets containing IPv6 HBH Options headers.

Finally, we note that the Routing Protocol for Low-Power and Lossy
Networks (RPL) routers [RFC6550] must not discard packets based on
the presence of an IPv6 Hop-by-Hop Options header, as this would
break the RPL.

3.5.2. Routing Header (Protocol Number=43)

3.5.2.1. Uses

The Routing Header is used by an IPv6 source to list one or more
intermediate nodes to be "visited" on the way to a packet's
destination.

3.5.2.2. Specification

This EH is specified in [RFC8200]. The Routing Type 0 had originally
been specified in [RFC2460] and was later obsoleted by [RFC5095];
thus, it was removed from [RFC8200].

As of May 2022, the following Routing Types have been specified:

* Type 0: Source Route (DEPRECATED) [RFC2460] [RFC5095]

* Type 1: Nimrod (DEPRECATED)

* Type 2: Type 2 Routing Header [RFC6275]

* Type 3: RPL Source Route Header [RFC6554]

* Type 4: Segment Routing Header (SRH) [RFC8754]

* Types 5-252: Unassigned

* Type 253: RFC3692-style Experiment 1 [RFC4727]

* Type 254: RFC3692-style Experiment 2 [RFC4727]

* Type 255: Reserved

3.5.2.3. Specific Security Implications

The security implications of Routing Headers of Routing Type 0 have
been discussed in detail in [Biondi-2007] and [RFC5095]. Routing
Type 1 was never widely implemented. The security implications of
Routing Headers of Routing Type 2, Routing Type 3, and Routing Type 4
(SRH) are discussed in [RFC6275], [RFC6554], and [RFC8754],
respectively.

3.5.2.4. Operational and Interoperability Impact If Blocked

Blocking packets containing Routing Headers of Routing Type 0 or
Routing Type 1 has no operational implications, since both have been
deprecated. Blocking packets containing Routing Headers of Routing
Type 2 would break Mobile IPv6. Packets containing Routing Headers
of Routing Type 3 may be safely blocked at RPL domain boundaries,
since such headers are employed within a single RPL domain. Blocking
packets containing Routing Headers of Routing Type 4 (SRH) will break
Segment Routing (SR) deployments if the filtering policy is enforced
on packets being forwarded within an SR domain.

3.5.2.5. Advice

Intermediate systems should discard packets containing Routing
Headers of Routing Type 0, Routing Type 1, or Routing Type 3. Other
Routing Types should be permitted, as required by [RFC7045].

3.5.3. Fragment Header (Protocol Number=44)

3.5.3.1. Uses

This EH provides the fragmentation and reassembly functionality for
IPv6.

3.5.3.2. Specification

This EH is specified in [RFC8200].

3.5.3.3. Specific Security Implications

The security implications of the Fragment Header range from DoS
attacks (e.g., based on flooding a target with IPv6 fragments) to
information leakage attacks [RFC7739].

3.5.3.4. Operational and Interoperability Impact If Blocked

Blocking packets that contain a Fragment Header will break any
protocol that may rely on fragmentation (e.g., the DNS [RFC1034]).
However, IP fragmentation is known to introduce fragility to Internet
communication [RFC8900].

3.5.3.5. Advice

Intermediate systems should permit packets that contain a Fragment
Header.

3.5.4. Encapsulating Security Payload (Protocol Number=50)

3.5.4.1. Uses

This EH is employed for the IPsec suite [RFC4303].

3.5.4.2. Specification

This EH is specified in [RFC4303].

3.5.4.3. Specific Security Implications

Besides the general implications of IPv6 EHs, this EH could be
employed to potentially perform a DoS attack at the destination
system by wasting CPU resources in validating the contents of the
packet.

3.5.4.4. Operational and Interoperability Impact If Blocked

Discarding packets that employ this EH would break IPsec deployments.

3.5.4.5. Advice

Intermediate systems should permit packets containing the
Encapsulating Security Payload EH.

3.5.5. Authentication Header (Protocol Number=51)

3.5.5.1. Uses

The Authentication Header can be employed to provide authentication
services in IPv4 and IPv6.

3.5.5.2. Specification

This EH is specified in [RFC4302].

3.5.5.3. Specific Security Implications

Besides the general implications of IPv6 EHs, this EH could be
employed to potentially perform a DoS attack at the destination
system by wasting CPU resources in validating the contents of the
packet.

3.5.5.4. Operational and Interoperability Impact If Blocked

Discarding packets that employ this EH would break IPsec deployments.

3.5.5.5. Advice

Intermediate systems should permit packets containing an
Authentication Header.

3.5.6. Destination Options (Protocol Number=60)

3.5.6.1. Uses

The Destination Options (DO) header is used to carry optional
information that needs be examined only by a packet's destination
node(s).

3.5.6.2. Specification

This EH is specified in [RFC8200]. As of May 2022, the following
options have been specified for this EH:

* Type 0x00: Pad1 [RFC8200]

* Type 0x01: PadN [RFC8200]

* Type 0x04: Tunnel Encapsulation Limit [RFC2473]

* Type 0x0F: IPv6 Performance and Diagnostic Metrics (PDM) [RFC8250]

* Type 0x4D: (Deprecated)

* Type 0xC9: Home Address [RFC6275]

* Type 0x8A: Endpoint Identification (Deprecated) [NIMROD-EID]

* Type 0x8B: ILNP Nonce [RFC6744]

* Type 0x8C: Line-Identification Option [RFC6788]

* Type 0x1E: RFC3692-style Experiment [RFC4727]

* Type 0x3E: RFC3692-style Experiment [RFC4727]

* Type 0x5E: RFC3692-style Experiment [RFC4727]

* Type 0x7E: RFC3692-style Experiment [RFC4727]

* Type 0x9E: RFC3692-style Experiment [RFC4727]

* Type 0xBE: RFC3692-style Experiment [RFC4727]

* Type 0xDE: RFC3692-style Experiment [RFC4727]

* Type 0xFE: RFC3692-style Experiment [RFC4727]

3.5.6.3. Specific Security Implications

No security implications are known, other than the general security
implications of IPv6 EHs. For a discussion of possible security
implications of specific options specified for the DO header, please
see Section 4.4.

3.5.6.4. Operational and Interoperability Impact If Blocked

Discarding packets that contain a Destination Options header would
break protocols that rely on this EH type for conveying information
(such as the Identifier-Locator Network Protocol (ILNP) [RFC6740] and
Mobile IPv6 [RFC6275]), as well as IPv6 tunnels that employ the
Tunnel Encapsulation Limit option [RFC2473].

3.5.6.5. Advice

Intermediate systems should permit packets that contain a Destination
Options header.

3.5.7. Mobility Header (Protocol Number=135)

3.5.7.1. Uses

The Mobility Header is an EH used by mobile nodes, correspondent
nodes, and home agents in all messaging related to the creation and
management of bindings in Mobile IPv6.

3.5.7.2. Specification

This EH is specified in [RFC6275].

3.5.7.3. Specific Security Implications

A thorough security assessment of the security implications of the
Mobility Header and related mechanisms can be found in Section 15 of
[RFC6275].

3.5.7.4. Operational and Interoperability Impact If Blocked

Discarding packets containing this EH would break Mobile IPv6.

3.5.7.5. Advice

Intermediate systems should permit packets that contain a Mobility
Header.

3.5.8. Host Identity Protocol (Protocol Number=139)

3.5.8.1. Uses

This EH is employed with the Host Identity Protocol (HIP), which is a
protocol that allows consenting hosts to securely establish and
maintain shared IP-layer state, allowing the separation of the
identifier and locator roles of IP addresses, thereby enabling
continuity of communications across IP address changes.

3.5.8.2. Specification

This EH is specified in [RFC7401].

3.5.8.3. Specific Security Implications

The security implications of the HIP header are discussed in detail
in Section 8 of [RFC7401].

3.5.8.4. Operational and Interoperability Impact If Blocked

Discarding packets that contain a HIP header would break HIP
deployments.

3.5.8.5. Advice

Intermediate systems should permit packets that contain a HIP header.

3.5.9. Shim6 Protocol (Protocol Number=140)

3.5.9.1. Uses

This EH is employed by the Shim6 protocol [RFC5533].

3.5.9.2. Specification

This EH is specified in [RFC5533].

3.5.9.3. Specific Security Implications

The specific security implications are discussed in detail in
Section 16 of [RFC5533].

3.5.9.4. Operational and Interoperability Impact If Blocked

Discarding packets that contain this EH will break Shim6.

3.5.9.5. Advice

Intermediate systems should permit packets containing this EH.

3.5.10. Use for Experimentation and Testing (Protocol Numbers=253 and
254)

3.5.10.1. Uses

These IPv6 EHs are employed for performing RFC3692-style experiments
(see [RFC3692] for details).

3.5.10.2. Specification

These EHs are specified in [RFC3692] and [RFC4727].

3.5.10.3. Specific Security Implications

The security implications of these EHs will depend on their specific
use.

3.5.10.4. Operational and Interoperability Impact If Blocked

For obvious reasons, discarding packets that contain these EHs limits
the ability to perform legitimate experiments across IPv6 routers.

3.5.10.5. Advice

Operators should determine, according to their own circumstances,
whether to discard packets containing these EHs.

3.6. Advice on the Handling of Packets with Unknown IPv6 Extension
Headers

We refer to IPv6 EHs that have not been assigned an Internet Protocol
number by IANA (and marked as such) in [IANA-PROTOCOLS] as "unknown
IPv6 Extension Headers" ("unknown IPv6 EHs").

3.6.1. Uses

New IPv6 EHs may be specified as part of future extensions to the
IPv6 protocol.

Since IPv6 EHs and upper-layer protocols employ the same namespace,
it is impossible to tell whether an unknown Internet Protocol number
is being employed for an IPv6 EH or an upper-layer protocol.

3.6.2. Specification

The processing of unknown IPv6 EHs is specified in [RFC7045].

3.6.3. Specific Security Implications

For obvious reasons, it is impossible to determine specific security
implications of unknown IPv6 EHs.

3.6.4. Operational and Interoperability Impact If Blocked

As noted in [RFC7045], discarding unknown IPv6 EHs may slow down the
deployment of new IPv6 EHs and transport protocols. The
corresponding IANA registry, which is [IANA-PROTOCOLS], should be
monitored such that filtering rules are updated as new IPv6 EHs are
standardized.

We note that since IPv6 EHs and upper-layer protocols share the same
numbering space, discarding unknown IPv6 EHs may result in packets
encapsulating unknown upper-layer protocols being discarded.

3.6.5. Advice

Operators should determine, according to their own circumstances,
whether to discard packets containing unknown IPv6 EHs.

4. IPv6 Options

4.1. General Discussion

The following subsections describe specific security implications of
different IPv6 options and provide advice regarding filtering packets
that contain such options.

4.2. General Security Implications of IPv6 Options

The general security implications of IPv6 options are closely related
to those discussed in Section 3.2 for IPv6 EHs. Essentially, packets
that contain IPv6 options might need to be processed by an IPv6
router's general-purpose CPU and, hence, could present a Distributed
Denial-of-Service (DDoS) risk to that router's general-purpose CPU
(and thus to the router itself). For some architectures, a possible
mitigation would be to rate-limit the packets that are to be
processed by the general-purpose CPU (see, e.g., [Cisco-EH]).

4.3. Summary of Advice on the Handling of IPv6 Packets with Specific
IPv6 Options

This section summarizes the advice provided in Section 4.4, and it
includes references to the specific sections in which a detailed
analysis can be found.

+===============================+======================+===========+
| Option | Filtering Policy | Reference |
+===============================+======================+===========+
| Pad1 (Type=0x00) | Permit | Section |
| | | 4.4.1 |
+-------------------------------+----------------------+-----------+
| PadN (Type=0x01) | Permit | Section |
| | | 4.4.2 |
+-------------------------------+----------------------+-----------+
| Tunnel Encapsulation Limit | Permit | Section |
| (Type=0x04) | | 4.4.3 |
+-------------------------------+----------------------+-----------+
| Router Alert (Type=0x05) | Permit based on | Section |
| | needed functionality | 4.4.4 |
+-------------------------------+----------------------+-----------+
| CALIPSO (Type=0x07) | Permit based on | Section |
| | needed functionality | 4.4.5 |
+-------------------------------+----------------------+-----------+
| SMF_DPD (Type=0x08) | Permit based on | Section |
| | needed functionality | 4.4.6 |
+-------------------------------+----------------------+-----------+
| PDM Option (Type=0x0F) | Permit | Section |
| | | 4.4.7 |
+-------------------------------+----------------------+-----------+
| RPL Option (Type=0x23) | Permit | Section |
| | | 4.4.8 |
+-------------------------------+----------------------+-----------+
| Quick-Start (Type=0x26) | Permit | Section |
| | | 4.4.9 |
+-------------------------------+----------------------+-----------+
| Deprecated (Type=0x4D) | Drop | Section |
| | | 4.4.10 |
+-------------------------------+----------------------+-----------+
| MPL Option (Type=0x6D) | Permit | Section |
| | | 4.4.12 |
+-------------------------------+----------------------+-----------+
| Jumbo Payload (Type=0xC2) | Permit based on | Section |
| | needed functionality | 4.4.16 |
+-------------------------------+----------------------+-----------+
| RPL Option (Type=0x63) | Drop | Section |
| | | 4.4.11 |
+-------------------------------+----------------------+-----------+
| Endpoint Identification | Drop | Section |
| (Type=0x8A) | | 4.4.13 |
+-------------------------------+----------------------+-----------+
| ILNP Nonce (Type=0x8B) | Permit | Section |
| | | 4.4.14 |
+-------------------------------+----------------------+-----------+
| Line-Identification Option | Drop | Section |
| (Type=0x8C) | | 4.4.15 |
+-------------------------------+----------------------+-----------+
| Home Address (Type=0xC9) | Permit | Section |
| | | 4.4.17 |
+-------------------------------+----------------------+-----------+
| IP_DFF (Type=0xEE) | Permit based on | Section |
| | needed functionality | 4.4.18 |
+-------------------------------+----------------------+-----------+
| RFC3692-style Experiment | Permit based on | Section |
| (Types = 0x1E, 0x3E, 0x5E, | needed functionality | 4.4.19 |
| 0x7E, 0x9E, 0xBE, 0xDE, 0xFE) | | |
+-------------------------------+----------------------+-----------+

Table 2: Summary of Advice on the Handling of IPv6 Packets with
Specific IPv6 Options

4.4. Advice on the Handling of Packets with Specific IPv6 Options

The following subsections contain a description of each of the IPv6
options that have so far been specified, a summary of the security
implications of each of such options, a discussion of possible
interoperability implications if packets containing such options are
discarded, and specific advice regarding whether packets containing
these options should be permitted.

4.4.1. Pad1 (Type=0x00)

4.4.1.1. Uses

This option is used when necessary to align subsequent options and to
pad out the containing header to a multiple of 8 octets in length.

4.4.1.2. Specification

This option is specified in [RFC8200].

4.4.1.3. Specific Security Implications

None.

4.4.1.4. Operational and Interoperability Impact If Blocked

Discarding packets that contain this option would potentially break
any protocol that relies on IPv6 options.

4.4.1.5. Advice

Intermediate systems should not discard packets based on the presence
of this option.

4.4.2. PadN (Type=0x01)

4.4.2.1. Uses

This option is used when necessary to align subsequent options and to
pad out the containing header to a multiple of 8 octets in length.

4.4.2.2. Specification

This option is specified in [RFC8200].

4.4.2.3. Specific Security Implications

Because of the possible size of this option, it could be leveraged as
a large-bandwidth covert channel.

4.4.2.4. Operational and Interoperability Impact If Blocked

Discarding packets that contain this option would potentially break
any protocol that relies on IPv6 options.

4.4.2.5. Advice

Intermediate systems should not discard IPv6 packets based on the
presence of this option.

4.4.3. Tunnel Encapsulation Limit (Type=0x04)

4.4.3.1. Uses

The Tunnel Encapsulation Limit option can be employed to specify how
many further levels of nesting the packet is permitted to undergo.

4.4.3.2. Specification

This option is specified in [RFC2473].

4.4.3.3. Specific Security Implications

These are discussed in [RFC2473].

4.4.3.4. Operational and Interoperability Impact If Blocked

Discarding packets based on the presence of this option could result
in tunnel traffic being discarded.

4.4.3.5. Advice

Intermediate systems should not discard packets based on the presence
of this option.

4.4.4. Router Alert (Type=0x05)

4.4.4.1. Uses

The Router Alert option [RFC2711] is employed by a number of
protocols, including the Resource reSerVation Protocol (RSVP)
[RFC2205], Multicast Listener Discovery (MLD) [RFC2710] [RFC3810],
Multicast Router Discovery (MRD) [RFC4286], and General Internet
Signaling Transport (GIST) [RFC5971]. Its usage is discussed in
detail in [RFC6398].

4.4.4.2. Specification

This option is specified in [RFC2711].

4.4.4.3. Specific Security Implications

Since this option causes the contents of the packet to be inspected
by the handling device, this option could be leveraged for performing
DoS attacks. The security implications of the Router Alert option
are discussed in detail in [RFC6398].

4.4.4.4. Operational and Interoperability Impact If Blocked

Discarding packets that contain this option would break any protocols
that rely on them, such as RSVP and multicast deployments. Please
see Section 4.4.4.3 for further details.

4.4.4.5. Advice

Packets containing this option should be permitted in environments
where support for RSVP, multicast routing, or similar protocols is
required.

4.4.5. CALIPSO (Type=0x07)

4.4.5.1. Uses

This option is used for encoding explicit packet Sensitivity Labels
on IPv6 packets. It is intended for use only within Multi-Level
Secure (MLS) networking environments that are both trusted and
trustworthy.

4.4.5.2. Specification

This option is specified in [RFC5570].

4.4.5.3. Specific Security Implications

Presence of this option in a packet does not by itself create any
specific new threat. Packets with this option ought not normally be
seen on the global public Internet.

4.4.5.4. Operational and Interoperability Impact If Blocked

If packets with this option are discarded or if the option is
stripped from the packet during transmission from source to
destination, then the packet itself is likely to be discarded by the
receiver because it is not properly labeled. In some cases, the
receiver might receive the packet but associate an incorrect
Sensitivity Label with the received data from the packet whose Common
Architecture Label IPv6 Security Option (CALIPSO) was stripped by a
middlebox (such as a packet scrubber). Associating an incorrect
Sensitivity Label can cause the received information to be handled
either as more sensitive than it really is ("upgrading") or as less
sensitive than it really is ("downgrading"), either of which is
problematic. As noted in [RFC5570], IPsec [RFC4301] [RFC4302]
[RFC4303] can be employed to protect the CALIPSO.

4.4.5.5. Advice

Recommendations for handling the CALIPSO depend on the deployment
environment rather than on whether an intermediate system happens to
be deployed as a transit device (e.g., IPv6 transit router).

Explicit configuration is the only method via which an intermediate
system can know whether that particular intermediate system has been
deployed within an MLS environment. In many cases, ordinary
commercial intermediate systems (e.g., IPv6 routers and firewalls)
are the majority of the deployed intermediate systems inside an MLS
network environment.

For intermediate systems that DO NOT implement [RFC5570], there
should be a configuration option to either (a) drop packets
containing the CALIPSO or (b) ignore the presence of the CALIPSO and
forward the packets normally. In non-MLS environments, such
intermediate systems should have this configuration option set to (a)
above. In MLS environments, such intermediate systems should have
this option set to (b) above. The default setting for this
configuration option should be set to (a) above, because MLS
environments are much less common than non-MLS environments.

For intermediate systems that DO implement [RFC5570], there should be
configuration options (a) and (b) from the preceding paragraph and
also a third configuration option (c) to process packets containing a
CALIPSO as per [RFC5570]. When deployed in non-MLS environments,
such intermediate systems should have this configuration option set
to (a) above. When deployed in MLS environments, such intermediate
systems should have this configuration option set to (c). The
default setting for this configuration option MAY be set to (a)
above, because MLS environments are much less common than non-MLS
environments.

4.4.6. SMF_DPD (Type=0x08)

4.4.6.1. Uses

This option is employed in the (experimental) Simplified Multicast
Forwarding (SMF) for unique packet identification for IPv6
Identification-based DPD (I-DPD) and as a mechanism to guarantee non-
collision of hash values for different packets when Hash-based DPD
(H-DPD) is used.

4.4.6.2. Specification

This option is specified in [RFC6621].

4.4.6.3. Specific Security Implications

None. The use of transient numeric identifiers is subject to the
security and privacy considerations discussed in [NUMERIC-IDS].

4.4.6.4. Operational and Interoperability Impact If Blocked

Dropping packets containing this option within a Mobile Ad Hoc
Network (MANET) domain would break SMF. However, dropping such
packets at the border of such domain would have no negative impact.

4.4.6.5. Advice

Intermediate systems that are not within a MANET domain should
discard packets that contain this option.

4.4.7. PDM (Type=0x0F)

4.4.7.1. Uses

This option is employed to convey sequence numbers and timing
information in IPv6 packets as a basis for measurements.

4.4.7.2. Specification

This option is specified in [RFC8250].

4.4.7.3. Specific Security Implications

These are discussed in [RFC8250]. Additionally, since this option
employs transient numeric identifiers, implementations may be subject
to the issues discussed in [NUMERIC-IDS].

4.4.7.4. Operational and Interoperability Impact If Blocked

Dropping packets containing this option will result in negative
interoperability implications for traffic employing this option as a
basis for measurements.

4.4.7.5. Advice

Intermediate systems should not discard packets based on the presence
of this option.

4.4.8. RPL Option (Type=0x23)

4.4.8.1. Uses

The RPL Option provides a mechanism to include routing information in
each datagram that a RPL router forwards.

4.4.8.2. Specification

This option is specified in [RFC9008].

4.4.8.3. Specific Security Implications

These are discussed in [RFC9008].

4.4.8.4. Operational and Interoperability Impact If Blocked

This option can survive outside of a RPL instance. As a result,
discarding packets based on the presence of this option would break
some use cases for RPL (see [RFC9008]).

4.4.8.5. Advice

Intermediate systems should not discard IPv6 packets based on the
presence of this option.

4.4.9. Quick-Start (Type=0x26)

4.4.9.1. Uses

This IP option is used in the specification of Quick-Start for TCP
and IP, which is an experimental mechanism that allows transport
protocols, in cooperation with routers, to determine an allowed
sending rate at the start and, at times, in the middle of a data
transfer (e.g., after an idle period) [RFC4782].

4.4.9.2. Specification

This option is specified in [RFC4782] on the "Experimental" track.

4.4.9.3. Specific Security Implications

Section 9.6 of [RFC4782] notes that Quick-Start is vulnerable to two
kinds of attacks:

* attacks to increase the routers' processing and state load and

* attacks with bogus Quick-Start Requests to temporarily tie up
available Quick-Start bandwidth, preventing routers from approving
Quick-Start Requests from other connections

We note that if routers in a given environment do not implement and
enable the Quick-Start mechanism, only the general security
implications of IP options (discussed in Section 4.2) would apply.

4.4.9.4. Operational and Interoperability Impact If Blocked

If packets with IPv6 Quick Start options are blocked, the host trying
to establish a TCP connection will fall back to not including the
Quick Start option -- this means that the feature will be disabled,
and additional delays in connection establishment will be introduced
(as discussed in Section 4.7.2 of [RFC4782]). We note, however, that
Quick-Start has been proposed as a mechanism that could be of use in
controlled environments and not as a mechanism that would be intended
or appropriate for ubiquitous deployment in the global Internet
[RFC4782].

4.4.9.5. Advice

Intermediate systems should not discard IPv6 packets based on the
presence of this option.

4.4.10. Deprecated (Type=0x4D)

4.4.10.1. Uses

No information has been found about this option type.

4.4.10.2. Specification

No information has been found about this option type.

4.4.10.3. Specific Security Implications

No information has been found about this option type; hence, it has
been impossible to perform the corresponding security assessment.

4.4.10.4. Operational and Interoperability Impact If Blocked

Unknown.

4.4.10.5. Advice

Intermediate systems should discard packets that contain this option.

4.4.11. RPL Option (Type=0x63)

4.4.11.1. Uses

The RPL Option provides a mechanism to include routing information in
each datagram that a RPL router forwards.

4.4.11.2. Specification

This option was originally specified in [RFC6553]. It has been
deprecated by [RFC9008].

4.4.11.3. Specific Security Implications

These are discussed in Section 5 of [RFC6553].

4.4.11.4. Operational and Interoperability Impact If Blocked

This option is meant to be employed within a RPL instance. As a
result, discarding packets based on the presence of this option
outside of a RPL instance will not result in interoperability
implications.

4.4.11.5. Advice

Intermediate systems should discard packets that contain a RPL
Option.

4.4.12. MPL Option (Type=0x6D)

4.4.12.1. Uses

This option is used with the Multicast Protocol for Low power and
Lossy Networks (MPL), which provides IPv6 multicast forwarding in
constrained networks.

4.4.12.2. Specification

This option is specified in [RFC7731] and is meant to be included
only in Hop-by-Hop Options headers.

4.4.12.3. Specific Security Implications

These are discussed in [RFC7731].

4.4.12.4. Operational and Interoperability Impact If Blocked

Dropping packets that contain an MPL Option within an MPL network
would break the MPL. However, dropping such packets at the border of
such networks will have no negative impact.

4.4.12.5. Advice

Intermediate systems should not discard packets based on the presence
of this option. However, since this option has been specified for
the Hop-by-Hop Options header, such systems should consider the
discussion in Section 3.5.1.

4.4.13. Endpoint Identification (Type=0x8A)

4.4.13.1. Uses

The Endpoint Identification option was meant to be used with the
Nimrod routing architecture [NIMROD-DOC] but has never seen
widespread deployment.

4.4.13.2. Specification

This option is specified in [NIMROD-DOC].

4.4.13.3. Specific Security Implications

Undetermined.

4.4.13.4. Operational and Interoperability Impact If Blocked

None.

4.4.13.5. Advice

Intermediate systems should discard packets that contain this option.

4.4.14. ILNP Nonce (Type=0x8B)

4.4.14.1. Uses

This option is employed by the Identifier-Locator Network Protocol
for IPv6 (ILNPv6) to provide protection against off-path attacks for
packets when ILNPv6 is in use and as a signal during initial network-
layer session creation that ILNPv6 is proposed for use with this
network-layer session, rather than classic IPv6.

4.4.14.2. Specification

This option is specified in [RFC6744].

4.4.14.3. Specific Security Implications

These are discussed in [RFC6744].

4.4.14.4. Operational and Interoperability Impact If Blocked

Discarding packets that contain this option will break ILNPv6
deployments.

4.4.14.5. Advice

Intermediate systems should not discard packets based on the presence
of this option.

4.4.15. Line-Identification Option (Type=0x8C)

4.4.15.1. Uses

This option is used by an Edge Router to identify the subscriber
premises in scenarios where several subscriber premises may be
logically connected to the same interface of an Edge Router.

4.4.15.2. Specification

This option is specified in [RFC6788].

4.4.15.3. Specific Security Implications

These are discussed in [RFC6788].

4.4.15.4. Operational and Interoperability Impact If Blocked

Since this option is meant to be used when tunneling Neighbor
Discovery messages in some broadband network deployment scenarios,
discarding packets based on the presence of this option at
intermediate systems will result in no interoperability implications.

4.4.15.5. Advice

Intermediate systems should discard packets that contain this option.

4.4.16. Jumbo Payload (Type=0XC2)

4.4.16.1. Uses

The Jumbo Payload option provides the means for supporting payloads
larger than 65535 bytes.

4.4.16.2. Specification

This option is specified in [RFC2675].

4.4.16.3. Specific Security Implications

There are no specific issues arising from this option, except for
improper validity checks of the option and associated packet lengths.

4.4.16.4. Operational and Interoperability Impact If Blocked

Discarding packets based on the presence of this option will cause
IPv6 jumbograms to be discarded.

4.4.16.5. Advice

An operator should permit this option only in specific scenarios in
which support for IPv6 jumbograms is required.

4.4.17. Home Address (Type=0xC9)

4.4.17.1. Uses

The Home Address option is used by a Mobile IPv6 node while away from
home to inform the recipient of the mobile node's home address.

4.4.17.2. Specification

This option is specified in [RFC6275].

4.4.17.3. Specific Security Implications

There are no (known) additional security implications, other than
those discussed in [RFC6275].

4.4.17.4. Operational and Interoperability Impact If Blocked

Discarding IPv6 packets based on the presence of this option will
break Mobile IPv6.

4.4.17.5. Advice

Intermediate systems should not discard IPv6 packets based on the
presence of this option.

4.4.18. IP_DFF (Type=0xEE)

4.4.18.1. Uses

This option is employed with the (experimental) Depth-First
Forwarding (DFF) in unreliable networks.

4.4.18.2. Specification

This option is specified in [RFC6971].

4.4.18.3. Specific Security Implications

These are specified in [RFC6971].

4.4.18.4. Operational and Interoperability Impact If Blocked

Dropping packets containing this option within a routing domain that
is running DFF would break DFF. However, dropping such packets at
the border of such domains will have no operational or
interoperability implications.

4.4.18.5. Advice

Intermediate systems that do not operate within a routing domain that
is running DFF should discard packets containing this option.

4.4.19. RFC3692-Style Experiment (Types = 0x1E, 0x3E, 0x5E, 0x7E, 0x9E,
0xBE, 0xDE, 0xFE)

4.4.19.1. Uses

These options can be employed for performing RFC3692-style
experiments. It is only appropriate to use these values in
explicitly configured experiments; they must not be shipped as
defaults in implementations.

4.4.19.2. Specification

These options are specified in [RFC4727] in the context of
RFC3692-style experiments.

4.4.19.3. Specific Security Implications

The specific security implications will depend on the specific use of
these options.

4.4.19.4. Operational and Interoperability Impact If Blocked

For obvious reasons, discarding packets that contain these options
limits the ability to perform legitimate experiments across IPv6
routers.

4.4.19.5. Advice

Operators should determine, according to their own circumstances,
whether to discard packets containing these IPv6 options.

4.5. Advice on the Handling of Packets with Unknown IPv6 Options

We refer to IPv6 options that have not been assigned an IPv6 Option
Type in the corresponding registry, which is [IANA-IPV6-PARAM], as
"unknown IPv6 options".

4.5.1. Uses

New IPv6 options may be specified as part of future protocol work.

4.5.2. Specification

The processing of unknown IPv6 options is specified in [RFC8200].

4.5.3. Specific Security Implications

For obvious reasons, it is impossible to determine specific security
implications of unknown IPv6 options.

4.5.4. Operational and Interoperability Impact If Blocked

Discarding unknown IPv6 options may slow down the deployment of new
IPv6 options. As noted in [IPv6-OPTIONS], the corresponding IANA
registry, which is [IANA-IPV6-PARAM], should be monitored such that
IPv6 option filtering rules are updated as new IPv6 options are
standardized.

4.5.5. Advice

Operators should determine, according to their own circumstances,
whether to discard packets containing unknown IPv6 options.

5. IANA Considerations

This document has no IANA actions.

6. Privacy Considerations

There are no privacy considerations associated with this document.

7. Security Considerations

This document provides advice on the filtering of IPv6 packets that
contain IPv6 EHs (and possibly IPv6 options) at IPv6 transit routers.
It is meant to improve the current situation of widespread dropping
of such IPv6 packets in those cases where the drops result from
improper configuration defaults or inappropriate advice in this area.

As discussed in Section 3.3, one of the underlying principles for the
advice provided in this document is that IPv6 packets with specific
EHs or options that may represent an attack vector for infrastructure
devices should be dropped. While this policy helps mitigate some
specific attack vectors, the recommendations in this document will
not help to mitigate vulnerabilities based on implementation errors
[RFC9098].

We also note that depending on the router architecture, attempts to
filter packets based on the presence of IPv6 EHs or options might
itself represent an attack vector to network infrastructure devices
[RFC9098].

8. References

8.1. Normative References

[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
September 1997, <https://www.rfc-editor.org/info/rfc2205>.

[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <https://www.rfc-editor.org/info/rfc2473>.

[RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
RFC 2675, DOI 10.17487/RFC2675, August 1999,
<https://www.rfc-editor.org/info/rfc2675>.

[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710,
DOI 10.17487/RFC2710, October 1999,
<https://www.rfc-editor.org/info/rfc2710>.

[RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, DOI 10.17487/RFC2711, October 1999,
<https://www.rfc-editor.org/info/rfc2711>.

[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692,
DOI 10.17487/RFC3692, January 2004,
<https://www.rfc-editor.org/info/rfc3692>.

[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.

[RFC4286] Haberman, B. and J. Martin, "Multicast Router Discovery",
RFC 4286, DOI 10.17487/RFC4286, December 2005,
<https://www.rfc-editor.org/info/rfc4286>.

[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.

[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.

[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.

[RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
ICMPv6, UDP, and TCP Headers", RFC 4727,
DOI 10.17487/RFC4727, November 2006,
<https://www.rfc-editor.org/info/rfc4727>.

[RFC4782] Floyd, S., Allman, M., Jain, A., and P. Sarolahti, "Quick-
Start for TCP and IP", RFC 4782, DOI 10.17487/RFC4782,
January 2007, <https://www.rfc-editor.org/info/rfc4782>.

[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>.

[RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
Shim Protocol for IPv6", RFC 5533, DOI 10.17487/RFC5533,
June 2009, <https://www.rfc-editor.org/info/rfc5533>.

[RFC5570] StJohns, M., Atkinson, R., and G. Thomas, "Common
Architecture Label IPv6 Security Option (CALIPSO)",
RFC 5570, DOI 10.17487/RFC5570, July 2009,
<https://www.rfc-editor.org/info/rfc5570>.

[RFC5971] Schulzrinne, H. and R. Hancock, "GIST: General Internet
Signalling Transport", RFC 5971, DOI 10.17487/RFC5971,
October 2010, <https://www.rfc-editor.org/info/rfc5971>.

[RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
2011, <https://www.rfc-editor.org/info/rfc6275>.

[RFC6398] Le Faucheur, F., Ed., "IP Router Alert Considerations and
Usage", BCP 168, RFC 6398, DOI 10.17487/RFC6398, October
2011, <https://www.rfc-editor.org/info/rfc6398>.

[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.

[RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
Power and Lossy Networks (RPL) Option for Carrying RPL
Information in Data-Plane Datagrams", RFC 6553,
DOI 10.17487/RFC6553, March 2012,
<https://www.rfc-editor.org/info/rfc6553>.

[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554,
DOI 10.17487/RFC6554, March 2012,
<https://www.rfc-editor.org/info/rfc6554>.

[RFC6621] Macker, J., Ed., "Simplified Multicast Forwarding",
RFC 6621, DOI 10.17487/RFC6621, May 2012,
<https://www.rfc-editor.org/info/rfc6621>.

[RFC6740] Atkinson, RJ. and SN. Bhatti, "Identifier-Locator Network
Protocol (ILNP) Architectural Description", RFC 6740,
DOI 10.17487/RFC6740, November 2012,
<https://www.rfc-editor.org/info/rfc6740>.

[RFC6744] Atkinson, RJ. and SN. Bhatti, "IPv6 Nonce Destination
Option for the Identifier-Locator Network Protocol for
IPv6 (ILNPv6)", RFC 6744, DOI 10.17487/RFC6744, November
2012, <https://www.rfc-editor.org/info/rfc6744>.

[RFC6788] Krishnan, S., Kavanagh, A., Varga, B., Ooghe, S., and E.
Nordmark, "The Line-Identification Option", RFC 6788,
DOI 10.17487/RFC6788, November 2012,
<https://www.rfc-editor.org/info/rfc6788>.

[RFC6971] Herberg, U., Ed., Cardenas, A., Iwao, T., Dow, M., and S.
Cespedes, "Depth-First Forwarding (DFF) in Unreliable
Networks", RFC 6971, DOI 10.17487/RFC6971, June 2013,
<https://www.rfc-editor.org/info/rfc6971>.

[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>.

[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>.

[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.

[RFC7731] Hui, J. and R. Kelsey, "Multicast Protocol for Low-Power
and Lossy Networks (MPL)", RFC 7731, DOI 10.17487/RFC7731,
February 2016, <https://www.rfc-editor.org/info/rfc7731>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[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>.

[RFC8250] Elkins, N., Hamilton, R., and M. Ackermann, "IPv6
Performance and Diagnostic Metrics (PDM) Destination
Option", RFC 8250, DOI 10.17487/RFC8250, September 2017,
<https://www.rfc-editor.org/info/rfc8250>.

[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.

[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>.

[RFC9008] Robles, M.I., Richardson, M., and P. Thubert, "Using RPI
Option Type, Routing Header for Source Routes, and IPv6-
in-IPv6 Encapsulation in the RPL Data Plane", RFC 9008,
DOI 10.17487/RFC9008, April 2021,
<https://www.rfc-editor.org/info/rfc9008>.

8.2. Informative References

[Biondi-2007]
Biondi, P. and A. Ebalard, "IPv6 Routing Header Security",
CanSecWest Security Conference, April 2007,
<http://www.secdev.org/conf/IPv6_RH_security-csw07.pdf>.

[Cisco-EH] Cisco Systems, "IPv6 Extension Headers Review and
Considerations", Whitepaper, October 2006,
<https://www.cisco.com/en/US/technologies/tk648/tk872/
technologies_white_paper0900aecd8054d37d.pdf>.

[FW-Benchmark]
Zack, E., "Firewall Security Assessment and Benchmarking
IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1,
Berlin, Germany, June 2013,
<https://www.ipv6hackers.org/files/meetings/ipv6-hackers-
1/zack-ipv6hackers1-firewall-security-assessment-and-
benchmarking.pdf>.

[Huston-2022]
Huston, G. and J. Damas, "IPv6 Fragmentation and EH
Behaviours", IEPG Meeting at IETF 113", March 2022,
<https://iepg.org/2022-03-20-ietf113/huston-v6frag.pdf>.

[IANA-IPV6-PARAM]
IANA, "Internet Protocol Version 6 (IPv6) Parameters",
<https://www.iana.org/assignments/ipv6-parameters>.

[IANA-PROTOCOLS]
IANA, "Protocol Numbers",
<https://www.iana.org/assignments/protocol-numbers>.

[IPv6-OPTIONS]
Gont, F., Liu, W., and R. P. Bonica, "Transmission and
Processing of IPv6 Options", Work in Progress, Internet-
Draft, draft-gont-6man-ipv6-opt-transmit-02, 21 August
2015, <https://datatracker.ietf.org/doc/html/draft-gont-
6man-ipv6-opt-transmit-02>.

[JAMES] Iurman, J., "Just Another Measurement of Extension header
Survivability (JAMES)", Work in Progress, Internet-Draft,
draft-vyncke-v6ops-james-02, 11 July 2022,
<https://datatracker.ietf.org/doc/html/draft-vyncke-v6ops-
james-02>.

[NIMROD-DOC]
"Nimrod Documentation",
<http://ana-3.lcs.mit.edu/~jnc/nimrod>.

[NIMROD-EID]
Lynn, C., "Endpoint Identifier Destination Option", Work
in Progress, Internet-Draft, draft-ietf-nimrod-eid-00, 2
March 1996, <https://datatracker.ietf.org/doc/html/draft-
ietf-nimrod-eid-00>.

[NUMERIC-IDS]
Gont, F. and I. Arce, "On the Generation of Transient
Numeric Identifiers", Work in Progress, Internet-Draft,
draft-irtf-pearg-numeric-ids-generation-11, 11 July 2022,
<https://datatracker.ietf.org/doc/html/draft-irtf-pearg-
numeric-ids-generation-11>.

[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>.

[RFC3871] Jones, G., Ed., "Operational Security Requirements for
Large Internet Service Provider (ISP) IP Network
Infrastructure", RFC 3871, DOI 10.17487/RFC3871, September
2004, <https://www.rfc-editor.org/info/rfc3871>.

[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>.

[RFC7126] Gont, F., Atkinson, R., and C. Pignataro, "Recommendations
on Filtering of IPv4 Packets Containing IPv4 Options",
BCP 186, RFC 7126, DOI 10.17487/RFC7126, February 2014,
<https://www.rfc-editor.org/info/rfc7126>.

[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>.

[RFC9098] Gont, F., Hilliard, N., Doering, G., Kumari, W., Huston,
G., and W. Liu, "Operational Implications of IPv6 Packets
with Extension Headers", RFC 9098, DOI 10.17487/RFC9098,
September 2021, <https://www.rfc-editor.org/info/rfc9098>.

Acknowledgements

The authors would like to thank Ron Bonica for his work on earlier
draft versions of this document.

The authors of this document would like to thank (in alphabetical
order) Mikael Abrahamsson, Brian Carpenter, Tim Chown, Roman Danyliw,
Darren Dukes, Lars Eggert, David Farmer, Mike Heard, Bob Hinden,
Christian Huitema, Benjamin Kaduk, Erik Kline, Murray Kucherawy, Jen
Linkova, Carlos Pignataro, Alvaro Retana, Maria Ines Robles,
Zaheduzzaman Sarker, Donald Smith, Pascal Thubert, Ole Troan, Gunter
Van de Velde, Éric Vyncke, and Robert Wilton for providing valuable
comments on earlier draft versions of this document.

This document borrows some text and analysis from [RFC7126], which is
authored by Fernando Gont, Randall Atkinson, and Carlos Pignataro.

The authors would like to thank Warren Kumari and Éric Vyncke for
their guidance during the publication process for this document.

Fernando would also like to thank Brian Carpenter and Ran Atkinson
who, over the years, have answered many questions and provided
valuable comments that have benefited his protocol-related work
(including the present document).

Authors' Addresses

Fernando Gont
SI6 Networks
Segurola y Habana 4310 7mo piso
Ciudad Autonoma de Buenos Aires
Argentina
Email: [email protected]
URI: https://www.si6networks.com

Will (Shucheng) Liu
Huawei Technologies
Bantian, Longgang District
Shenzhen
518129
China
Email: [email protected]