draft-ietf-opsec-ipv6-eh-filtering-09.txt		draft-ietf-opsec-ipv6-eh-filtering-10.txt
	opsec F. Gont		opsec F. Gont
	Internet-Draft SI6 Networks		Internet-Draft EdgeUno
	Intended status: Informational W. Liu		Intended status: Informational W. Liu
	Expires: 3 November 2022 Huawei Technologies		Expires: 4 November 2022 Huawei Technologies
	2 May 2022		3 May 2022
	Recommendations on the Filtering of IPv6 Packets Containing IPv6		Recommendations on the Filtering of IPv6 Packets Containing IPv6
	Extension Headers at Transit Routers		Extension Headers at Transit Routers
	draft-ietf-opsec-ipv6-eh-filtering-09		draft-ietf-opsec-ipv6-eh-filtering-10
	Abstract		Abstract
	This document analyzes the security implications of IPv6 Extension		This document analyzes the security implications of IPv6 Extension
	Headers and associated IPv6 options. Additionally, it discusses the		Headers and associated IPv6 options. Additionally, it discusses the
	operational and interoperability implications of discarding packets		operational and interoperability implications of discarding packets
	based on the IPv6 Extension Headers and IPv6 options they contain.		based on the IPv6 Extension Headers and IPv6 options they contain.
	Finally, it provides advice on the filtering of such IPv6 packets at		Finally, it provides advice on the filtering of such IPv6 packets at
	transit routers for traffic *not* directed to them, for those cases		transit routers for traffic not directed to them, for those cases
	where such filtering is deemed as necessary.		where such filtering is deemed as necessary.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on 3 November 2022.		This Internet-Draft will expire on 4 November 2022.
	Copyright Notice		Copyright Notice
	Copyright (c) 2022 IETF Trust and the persons identified as the		Copyright (c) 2022 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents (https://trustee.ietf.org/		Provisions Relating to IETF Documents (https://trustee.ietf.org/
	license-info) in effect on the date of publication of this document.		license-info) in effect on the date of publication of this document.
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	and restrictions with respect to this document. Code Components		and restrictions with respect to this document. Code Components
	extracted from this document must include Revised BSD License text as		extracted from this document must include Revised BSD License text as
	described in Section 4.e of the Trust Legal Provisions and are		described in Section 4.e of the Trust Legal Provisions and are
	provided without warranty as described in the Revised BSD License.		provided without warranty as described in the Revised BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Terminology and Conventions Used in This Document . . . . . . 4		2. Terminology and Assumptions Employed in This Document . . . . 4
	2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4		2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
	2.2. Applicability Statement . . . . . . . . . . . . . . . . . 4		2.2. Applicability Statement . . . . . . . . . . . . . . . . . 4
	2.3. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4		2.3. Router Default Behavior and Features . . . . . . . . . . 4
	3. IPv6 Extension Headers . . . . . . . . . . . . . . . . . . . 5		3. IPv6 Extension Headers . . . . . . . . . . . . . . . . . . . 5
	3.1. General Discussion . . . . . . . . . . . . . . . . . . . 5		3.1. General Discussion . . . . . . . . . . . . . . . . . . . 5
	3.2. General Security Implications . . . . . . . . . . . . . . 6		3.2. General Security Implications . . . . . . . . . . . . . . 6
	3.3. Summary of Advice on the Handling of IPv6 Packets with		3.3. Rationale for Our Advice on the Handling of IPv6 Packets
			with Specific IPv6 Extension Headers . . . . . . . . . . 6
			3.4. Summary of Advice on the Handling of IPv6 Packets with
	Specific IPv6 Extension Headers . . . . . . . . . . . . . 6		Specific IPv6 Extension Headers . . . . . . . . . . . . . 6
	3.4. Advice on the Handling of IPv6 Packets with Specific IPv6		3.5. Advice on the Handling of IPv6 Packets with Specific IPv6
	Extension Headers . . . . . . . . . . . . . . . . . . . . 7		Extension Headers . . . . . . . . . . . . . . . . . . . . 7
	3.5. Advice on the Handling of Packets with Unknown IPv6		3.6. Advice on the Handling of Packets with Unknown IPv6
	Extension Headers . . . . . . . . . . . . . . . . . . . . 16		Extension Headers . . . . . . . . . . . . . . . . . . . . 16
	4. IPv6 Options . . . . . . . . . . . . . . . . . . . . . . . . 17		4. IPv6 Options . . . . . . . . . . . . . . . . . . . . . . . . 17
	4.1. General Discussion . . . . . . . . . . . . . . . . . . . 17		4.1. General Discussion . . . . . . . . . . . . . . . . . . . 17
	4.2. General Security Implications of IPv6 Options . . . . . . 17		4.2. General Security Implications of IPv6 Options . . . . . . 17
	4.3. Advice on the Handling of Packets with Specific IPv6		4.3. Summary of Advice on the Handling of IPv6 Packets with
	Options . . . . . . . . . . . . . . . . . . . . . . . . . 18		Specific IPv6 Extension Headers . . . . . . . . . . . . . 18
	4.4. Advice on the handling of Packets with Unknown IPv6		4.4. Advice on the Handling of Packets with Specific IPv6
	Options . . . . . . . . . . . . . . . . . . . . . . . . . 30		Options . . . . . . . . . . . . . . . . . . . . . . . . . 19
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30		4.5. Advice on the handling of Packets with Unknown IPv6
	6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 30		Options . . . . . . . . . . . . . . . . . . . . . . . . . 32
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 31		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
	8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31		6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 32
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . 31		7. Security Considerations . . . . . . . . . . . . . . . . . . . 32
	9.1. Normative References . . . . . . . . . . . . . . . . . . 31		8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 33
	9.2. Informative References . . . . . . . . . . . . . . . . . 35		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37		9.1. Normative References . . . . . . . . . . . . . . . . . . 33
			9.2. Informative References . . . . . . . . . . . . . . . . . 37
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 39
	1. Introduction		1. Introduction
	IPv6 Extension Headers (EHs) allow for the extension of the IPv6		IPv6 Extension Headers (EHs) allow for the extension of the IPv6
	protocol, and provide support for core functionality such as IPv6		protocol, and provide support for core functionality such as IPv6
	fragmentation. However, common implementation limitations suggest		fragmentation. However, common implementation limitations suggest
	that EHs present a challenge for IPv6 packet routing equipment,		that EHs present a challenge for IPv6 packet routing equipment,
	particularly when the IPv6 header chain needs to be processed for		particularly when the IPv6 header chain needs to be processed for
	e.g. enforcing ACLs or implementing other functions [RFC9098].		e.g. enforcing ACLs or implementing other functions [RFC9098].
	Recent studies (see e.g. [RFC7872]) suggest that there is widespread		Several studies (e.g. [Huston-2022], [I-D.vyncke-v6ops-james], and
	dropping of IPv6 packets that contain IPv6 Extension Headers (EHs).		[RFC7872]) suggest that there is widespread dropping of IPv6 packets
	In some cases, such packet drops occur at transit routers. While		that contain IPv6 Extension Headers (EHs). In some cases, such
	some operators "officially" drop packets that contain IPv6 EHs, it is		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		possible that some of the measured packet drops are the result of
	improper configuration defaults, or inappropriate advice in this		inappropriate advice in this area.
	area.
	This document analyzes both the general security implications of IPv6		This document analyzes both the general security implications of IPv6
	EHs, as well as the security implications of specific EH and Option		EHs, as well as the security implications of specific EH and Option
	types. It also provides advice on the filtering of IPv6 packets		types. It also provides advice on the filtering of IPv6 packets
	based on the IPv6 EHs and the IPv6 options they contain. Since		based on the IPv6 EHs and the IPv6 options they contain. Since
	various protocols may use IPv6 EHs (possibly with IPv6 options),		various protocols may use IPv6 EHs (possibly with IPv6 options),
	discarding packets based on the IPv6 EHs or IPv6 options they contain		discarding packets based on the IPv6 EHs or IPv6 options they contain
	can have implications on the proper functioning of such protocols.		can have implications on the proper functioning of such protocols.
	Thus, this document also attempts to discuss the operational and		Thus, this document also attempts to discuss the operational and
	interoperability implications of such filtering policies.		interoperability implications of such filtering policies.
	skipping to change at page 3, line 29 ¶		skipping to change at page 3, line 33 ¶
	The resulting packet filtering policy typically depends on where in		The resulting packet filtering policy typically depends on where in
	the network such policy is enforced: when the policy is enforced in a		the network such policy is enforced: when the policy is enforced in a
	transit network, the policy typically follows a "deny-list" approach,		transit network, the policy typically follows a "deny-list" approach,
	where only packets with clear negative implications are dropped. On		where only packets with clear negative implications are dropped. On
	the other hand, when the policy is enforced closer to the destination		the other hand, when the policy is enforced closer to the destination
	systems, the policy typically follows an "accept-list" approach,		systems, the policy typically follows an "accept-list" approach,
	where only traffic that is expected to be received is allowed. The		where only traffic that is expected to be received is allowed. The
	advice in this document is aimed only at transit routers that may		advice in this document is aimed only at transit routers that may
	need to enforce a filtering policy based on the EHs and IPv6 options		need to enforce a filtering policy based on the EHs and IPv6 options
	a packet may contain, following a "deny-list" approach, and hence is		a packet may contain, following a "deny-list" approach, and hence is
	likely to be much more permissive that a filtering policy to be		likely to be much more permissive than a filtering policy to be
	employed at e.g. the edge of an enterprise network. The advice in		employed at e.g. the edge of an enterprise network. The advice in
	this document is meant to improve the current situation of the		this document is meant to improve the current situation of the
	dropping of packets with IPv6 EHs in the Internet [RFC7872] in such		dropping of packets with IPv6 EHs in the Internet [RFC7872] in such
	cases where packets are being dropped due to inappropriate or missing		cases where packets are being dropped due to inappropriate or missing
	guidelines.		guidelines.
	This document is similar in nature to [RFC7126], which addresses the		This document is similar in nature to [RFC7126], which addresses the
	same problem for the IPv4 case. However, in IPv6, the problem space		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,		is compounded by the fact that IPv6 specifies a number of IPv6 EHs,
	and a number of IPv6 options which may be valid only when included in		and a number of IPv6 options which may be valid only when included in
	specific EH types.		specific EH types.
	This document completes and complements the considerations for		This document completes and complements the considerations for
	protecting the control plane from packets containing IP options that		protecting the control plane from packets containing IP options that
	can be found in [RFC6192].		can be found in [RFC6192].
	Section 2 of this document specifies the terminology and conventions		Section 2 specifies the terminology and conventions employed
	employed throughout this document. Section 3 of this document		throughout this document. Section 3 discusses IPv6 EHs and provides
	discusses IPv6 EHs and provides advice in the area of filtering IPv6		advice in the area of filtering IPv6 packets that contain such IPv6
	packets that contain such IPv6 EHs. Section 4 of this document		EHs. Section 4 discusses IPv6 options and provides advice in the
	discusses IPv6 options and provides advice in the area of filtering		area of filtering IPv6 packets that contain such options.
	IPv6 packets that contain such options.
	2. Terminology and Conventions Used in This Document		2. Terminology and Assumptions Employed in This Document
	2.1. Terminology		2.1. Terminology
	The terms "permit" (allow the traffic), "drop" (drop with no		The terms "permit" (allow the traffic), "drop" (drop with no
	notification to sender), and "reject" (drop with appropriate		notification to sender), and "reject" (drop with appropriate
	notification to sender) are employed as defined in [RFC3871].		notification to sender) are employed as defined in [RFC3871].
	Throughout this document we also employ the term "discard" as a		Throughout this document we also employ the term "discard" as a
	generic term to indicate the act of discarding a packet, irrespective		generic term to indicate the act of discarding a packet, irrespective
	of whether the sender is notified of such drops, and irrespective of		of whether the sender is notified of such drops, and irrespective of
	whether the specific filtering action is logged.		whether the specific filtering action is logged.
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	2.2. Applicability Statement		2.2. Applicability Statement
	This document provides advice on the filtering of IPv6 packets with		This document provides advice on the filtering of IPv6 packets with
	EHs at transit routers for traffic *not* explicitly destined to them,		EHs at transit routers for traffic not explicitly destined to them,
	for cases in which such filtering is deemed as necessary.		for cases in which such filtering is deemed as necessary.
	2.3. Conventions		2.3. Router Default Behavior and Features
	This document assumes that nodes comply with the requirements in		This document assumes that nodes comply with the requirements in
	[RFC7045]. Namely,		[RFC7045]. Namely,
	"If a forwarding node discards a packet containing a standard IPv6		"If a forwarding node discards a packet containing a standard IPv6
	extension header, it MUST be the result of a configurable policy		extension header, it MUST be the result of a configurable policy
	and not just the result of a failure to recognise such a header.		and not just the result of a failure to recognise such a header.
	This means that the discard policy for each standard type of		This means that the discard policy for each standard type of
	extension header MUST be individually configurable. The default		extension header MUST be individually configurable. The default
	configuration SHOULD allow all standard extension headers."		configuration SHOULD allow all standard extension headers."
	The advice provided in this document is only meant to guide an		The advice provided in this document is only meant to guide an
	operator in configuring forwarding devices, and is *not* to be		operator in configuring forwarding devices, and is not to be
	interpreted as advice regarding default configuration settings for		interpreted as advice regarding default configuration settings for
	network devices. That is, this document provides advice with respect		network devices. That is, this document provides advice with respect
	to operational configurations, but does not change the implementation		to operational policies, but does not change the implementation
	defaults required by [RFC7045].		defaults required by [RFC7045].
	We recommend that configuration options are made available to govern		We recommend that configuration options are made available to govern
	the processing of each IPv6 EH type and each IPv6 option type. Such		the processing of each IPv6 EH type and each IPv6 option type. Such
	configuration options should include the following possible settings:		configuration options should include the following possible settings:
	* Permit this IPv6 EH or IPv6 Option type.		* Permit this IPv6 EH or IPv6 Option type.
	* Drop (and log) packets containing this IPv6 EH or option type.		* Drop packets containing this IPv6 EH or option type.
	* Reject (and log) packets containing this IPv6 EH or option type		* Reject packets containing this IPv6 EH or option type (where the
	(where the packet drop is signaled with an ICMPv6 error message).		packet drop is signaled with an ICMPv6 error message).
	* Rate-limit traffic containing this IPv6 EH or option type.		* Rate-limit traffic containing this IPv6 EH or option type.
	* Ignore this IPv6 EH or option type (as if it was not present) and		* Ignore this IPv6 EH or option type (as if it was not present) and
	process the packet according the rules for the remaining headers.		process the packet according the rules for the remaining headers.
	We note that if a packet carries forwarding information (e.g., in		We note that if a packet carries forwarding information (e.g., in
	an IPv6 Routing Header) this might be an inappropriate or		an IPv6 Routing Header) this might be an inappropriate or
	undesirable action.		undesirable action.
	We note that special care needs to be taken when devices log packet		We note that special care needs to be taken when devices log packet
	skipping to change at page 6, line 19 ¶		skipping to change at page 6, line 25 ¶
	In some device architectures, IPv6 packets that contain IPv6 EHs can		In some device architectures, IPv6 packets that contain IPv6 EHs can
	cause the corresponding packets to be processed on the slow path, and		cause the corresponding packets to be processed on the slow path, and
	hence may be leveraged for the purpose of Denial of Service (DoS)		hence may be leveraged for the purpose of Denial of Service (DoS)
	attacks [RFC9098] [Cisco-EH] [FW-Benchmark].		attacks [RFC9098] [Cisco-EH] [FW-Benchmark].
	Operators are urged to consider the IPv6 EH and IPv6 options handling		Operators are urged to consider the IPv6 EH and IPv6 options handling
	capabilities of their devices as they make deployment decisions in		capabilities of their devices as they make deployment decisions in
	the future.		the future.
	3.3. Summary of Advice on the Handling of IPv6 Packets with Specific		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 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		IPv6 Extension Headers
	This section summarizes the advice provided in Section 3.4, providing		This section summarizes the advice provided in Section 3.5, providing
	references to the specific sections in which a detailed analysis can		references to the specific sections in which a detailed analysis can
	be found.		be found.
	+=========================+==========================+===========+		+=========================+==========================+===========+
	| EH type | Filtering policy | Reference |		| EH type | Filtering policy | Reference |
	+=========================+==========================+===========+		+=========================+==========================+===========+
	| IPv6 Hop-by-Hop Options | Drop or Ignore | Section |		| IPv6 Hop-by-Hop Options | Drop or Ignore | Section |
	| (Proto=0) | | 3.4.1 |		| (Proto=0) | | 3.5.1 |
	+-------------------------+--------------------------+-----------+		+-------------------------+--------------------------+-----------+
	| Routing Header for IPv6 | Drop only RHT0 and RHT1. | Section |		| Routing Header for IPv6 | Drop only RHT0 and RHT1. | Section |
	| (Proto=43) | Permit other RH Types | 3.4.2 |		| (Proto=43) | Permit other RH Types | 3.5.2 |
	+-------------------------+--------------------------+-----------+		+-------------------------+--------------------------+-----------+
	| Fragment Header for | Permit | Section |		| Fragment Header for | Permit | Section |
	| IPv6 (Proto=44) | | 3.4.3 |		| IPv6 (Proto=44) | | 3.5.3 |
	+-------------------------+--------------------------+-----------+		+-------------------------+--------------------------+-----------+
	| Encapsulating Security | Permit | Section |		| Encapsulating Security | Permit | Section |
	| Payload (Proto=50) | | 3.4.4 |		| Payload (Proto=50) | | 3.5.4 |
	+-------------------------+--------------------------+-----------+		+-------------------------+--------------------------+-----------+
	| Authentication Header | Permit | Section |		| Authentication Header | Permit | Section |
	| (Proto=51) | | 3.4.5 |		| (Proto=51) | | 3.5.5 |
	+-------------------------+--------------------------+-----------+		+-------------------------+--------------------------+-----------+
	| Destination Options for | Permit | Section |		| Destination Options for | Permit | Section |
	| IPv6 (Proto=60) | | 3.4.6 |		| IPv6 (Proto=60) | | 3.5.6 |
	+-------------------------+--------------------------+-----------+		+-------------------------+--------------------------+-----------+
	| Mobility Header | Permit | Section |		| Mobility Header | Permit | Section |
	| (Proto=135) | | 3.4.7 |		| (Proto=135) | | 3.5.7 |
	+-------------------------+--------------------------+-----------+		+-------------------------+--------------------------+-----------+
	| Host Identity Protocol | Permit | Section |		| Host Identity Protocol | Permit | Section |
	| (Proto=139) | | 3.4.8 |		| (Proto=139) | | 3.5.8 |
	+-------------------------+--------------------------+-----------+		+-------------------------+--------------------------+-----------+
	| Shim6 Protocol | Permit | Section |		| Shim6 Protocol | Permit | Section |
	| (Proto=140) | | 3.4.9 |		| (Proto=140) | | 3.5.9 |
	+-------------------------+--------------------------+-----------+		+-------------------------+--------------------------+-----------+
	| Use for experimentation | Drop | Section |		| Use for experimentation | Drop | Section |
	| and testing (Proto=253 | | 3.4.10 |		| and testing (Proto=253 | | 3.5.10 |
	| and 254) | | |		| and 254) | | |
	+-------------------------+--------------------------+-----------+		+-------------------------+--------------------------+-----------+
	Table 1: Summary of Advice on the Handling of IPv6 Packets		Table 1: Summary of Advice on the Handling of IPv6 Packets
	with Specific IPv6 Extension Headers		with Specific IPv6 Extension Headers
	3.4. Advice on the Handling of IPv6 Packets with Specific IPv6		3.5. Advice on the Handling of IPv6 Packets with Specific IPv6
	Extension Headers		Extension Headers
	3.4.1. IPv6 Hop-by-Hop Options (Protocol Number=0)		3.5.1. IPv6 Hop-by-Hop Options (Protocol Number=0)
	3.4.1.1. Uses		3.5.1.1. Uses
	The Hop-by-Hop Options header is used to carry optional information		The Hop-by-Hop Options header is used to carry optional information
	that may be examined by every node along a packet's delivery path.		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		It is expected that nodes will examine the Hop-by-Hop Options header
	if explicitly configured to do so.		if explicitly configured to do so.
	NOTE: A previous revision of the IPv6 core specification, [RFC2460],		NOTE: A previous revision of the IPv6 core specification, [RFC2460],
	originally required that all nodes examined and processed the Hop-by-		originally required that all nodes examined and processed the Hop-by-
	Hop Options header. However, even before the publication of		Hop Options header. However, even before the publication of
	[RFC8200] a number of implementations already provided the option of		[RFC8200] a number of implementations already provided the option of
	ignoring this header unless explicitly configured to examine it.		ignoring this header unless explicitly configured to examine it.
	3.4.1.2. Specification		3.5.1.2. Specification
	This EH is specified in [RFC8200]. At the time of this writing, the		This EH is specified in [RFC8200]. As of May 2022, the following
	following options have been specified for the Hop-by-Hop Options EH:		options have been specified for the Hop-by-Hop Options EH:
	* Type 0x00: Pad1 [RFC8200]		* Type 0x00: Pad1 [RFC8200]
	* Type 0x01: PadN [RFC8200]		* Type 0x01: PadN [RFC8200]
	* Type 0x05: Router Alert [RFC2711]		* Type 0x05: Router Alert [RFC2711]
	* Type 0x07: CALIPSO [RFC5570]		* Type 0x07: CALIPSO [RFC5570]
	* Type 0x08: SMF_DPD [RFC6621]		* Type 0x08: SMF_DPD [RFC6621]
	skipping to change at page 9, line 16 ¶		skipping to change at page 9, line 16 ¶
	* Type 0x7E: RFC3692-style Experiment [RFC4727]		* Type 0x7E: RFC3692-style Experiment [RFC4727]
	* Type 0x9E: RFC3692-style Experiment [RFC4727]		* Type 0x9E: RFC3692-style Experiment [RFC4727]
	* Type 0xBE: RFC3692-style Experiment [RFC4727]		* Type 0xBE: RFC3692-style Experiment [RFC4727]
	* Type 0xDE: RFC3692-style Experiment [RFC4727]		* Type 0xDE: RFC3692-style Experiment [RFC4727]
	* Type 0xFE: RFC3692-style Experiment [RFC4727]		* Type 0xFE: RFC3692-style Experiment [RFC4727]
	3.4.1.3. Specific Security Implications		3.5.1.3. Specific Security Implications
	Legacy nodes that process this extension header might be subject to		Legacy nodes that process this extension header might be subject to
	Denial of Service attacks.		Denial of Service attacks.
	NOTE: While [RFC8200] has removed this requirement, the deployed base		NOTE: While [RFC8200] has removed this requirement, the deployed base
	may still reflect the classical behavior for a while, and hence the		may still reflect the classical behavior for a while, and hence the
	potential security problems of this EH are still of concern.		potential security problems of this EH are still of concern.
	3.4.1.4. Operational and Interoperability Impact if Blocked		3.5.1.4. Operational and Interoperability Impact if Blocked
	Discarding packets containing a Hop-by-Hop Options EH would break any		Discarding packets containing a Hop-by-Hop Options EH would break any
	of the protocols that rely on it for proper functioning. For		of the protocols that rely on it for proper functioning. For
	example, it would break RSVP [RFC2205] and multicast deployments, and		example, it would break RSVP [RFC2205] and multicast deployments, and
	would cause IPv6 jumbograms to be discarded.		would cause IPv6 jumbograms to be discarded.
	3.4.1.5. Advice		3.5.1.5. Advice
	Nodes implementing [RFC8200] would already ignore this extension		Nodes implementing [RFC8200] would already ignore this extension
	header unless explicitly required to process it. For legacy		header unless explicitly required to process it. For legacy
	([RFC2460]) nodes, the recommended configuration for the processing		([RFC2460]) nodes, the recommended configuration for the processing
	of these packets depends on the features and capabilities of the		of these packets depends on the features and capabilities of the
	underlying platform, the configuration of the platform, and also the		underlying platform, the configuration of the platform, and also the
	deployment environment of the platform. On platforms that allow		deployment environment of the platform. On platforms that allow
	forwarding of packets with HBH Options on the fast path, we recommend		forwarding of packets with HBH Options on the fast path, we recommend
	that packets with a HBH Options EH be forwarded as normal.		that packets with a HBH Options EH be forwarded as normal.
	Otherwise, on platforms in which processing of packets with a IPv6		Otherwise, on platforms in which processing of packets with a IPv6
	skipping to change at page 10, line 9 ¶		skipping to change at page 10, line 9 ¶
	be selected. Finally, when packets containing a HBH Options EH are		be selected. Finally, when packets containing a HBH Options EH are
	processed in the slow-path, and the underlying platform does not have		processed in the slow-path, and the underlying platform does not have
	any mitigation options available for attacks based on these packets,		any mitigation options available for attacks based on these packets,
	we recommend that such platforms discard packets containing IPv6 HBH		we recommend that such platforms discard packets containing IPv6 HBH
	Options EHs.		Options EHs.
	Finally, we note that RPL (Routing Protocol for Low-Power and Lossy		Finally, we note that RPL (Routing Protocol for Low-Power and Lossy
	Networks) routers [RFC6550] must not discard packets based on the		Networks) routers [RFC6550] must not discard packets based on the
	presence of an IPv6 Hop-by-Hop Options EH, as this would break RPL.		presence of an IPv6 Hop-by-Hop Options EH, as this would break RPL.
	3.4.2. Routing Header for IPv6 (Protocol Number=43)		3.5.2. Routing Header for IPv6 (Protocol Number=43)
	3.4.2.1. Uses		3.5.2.1. Uses
	The Routing header is used by an IPv6 source to list one or more		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		intermediate nodes to be "visited" on the way to a packet's
	destination.		destination.
	3.4.2.2. Specification		3.5.2.2. Specification
	This EH is specified in [RFC8200]. [RFC2460] had originally		This EH is specified in [RFC8200]. [RFC2460] had originally
	specified the Routing Header Type 0, which was later obsoleted by		specified the Routing Header Type 0, which was later obsoleted by
	[RFC5095], and thus removed from [RFC8200].		[RFC5095], and thus removed from [RFC8200].
	At the time of this writing, the following Routing Types have been		At of May 2022, the following Routing Types have been specified:
	specified:
	* Type 0: Source Route (DEPRECATED) [RFC2460] [RFC5095]		* Type 0: Source Route (DEPRECATED) [RFC2460] [RFC5095]
	* Type 1: Nimrod (DEPRECATED)		* Type 1: Nimrod (DEPRECATED)
	* Type 2: Type 2 Routing Header [RFC6275]		* Type 2: Type 2 Routing Header [RFC6275]
	* Type 3: RPL Source Route Header [RFC6554]		* Type 3: RPL Source Route Header [RFC6554]
	* Type 4: Segment Routing Header (SRH) [RFC8754]		* Type 4: Segment Routing Header (SRH) [RFC8754]
	* Types 5-252: Unassigned		* Types 5-252: Unassigned
	* Type 253: RFC3692-style Experiment 1 [RFC4727]		* Type 253: RFC3692-style Experiment 1 [RFC4727]
	* Type 254: RFC3692-style Experiment 2 [RFC4727]		* Type 254: RFC3692-style Experiment 2 [RFC4727]
	* Type 255: Reserved		* Type 255: Reserved
	3.4.2.3. Specific Security Implications		3.5.2.3. Specific Security Implications
	The security implications of RHT0 have been discussed in detail in		The security implications of RHT0 have been discussed in detail in
	[Biondi2007] and [RFC5095]. RHT1 was never widely implemented. The		[Biondi2007] and [RFC5095]. RHT1 was never widely implemented. The
	security implications of RHT2, RHT3, and RHT4 (SRH) are discussed in		security implications of RHT2, RHT3, and RHT4 (SRH) are discussed in
	[RFC6275], [RFC6554], and [RFC8754], respectively.		[RFC6275], [RFC6554], and [RFC8754], respectively.
	3.4.2.4. Operational and Interoperability Impact if Blocked		3.5.2.4. Operational and Interoperability Impact if Blocked
	Blocking packets containing a RHT0 or RHT1 has no operational		Blocking packets containing a RHT0 or RHT1 has no operational
	implications, since both have been deprecated. Blocking packets with		implications, since both have been deprecated. Blocking packets with
	a RHT2 would break Mobile IPv6. Packets with a RHT3 may be safely		a RHT2 would break Mobile IPv6. Packets with a RHT3 may be safely
	blocked at RPL domain boundaries, since RHT3 headers are employed		blocked at RPL domain boundaries, since RHT3 headers are employed
	within a single RPL domain. Blocking packets with a RHT4 (SRH) will		within a single RPL domain. Blocking packets with a RHT4 (SRH) will
	break Segment Routing (SR) deployments, if the filtering policy is		break Segment Routing (SR) deployments, if the filtering policy is
	enforced on packets being forwarded within an SR domain.		enforced on packets being forwarded within an SR domain.
	3.4.2.5. Advice		3.5.2.5. Advice
	Intermediate systems should discard packets containing a RHT0, RHT1,		Intermediate systems should discard packets containing a RHT0, RHT1,
	or RHT3. Other routing header types should be permitted, as required		or RHT3. Other routing header types should be permitted, as required
	by [RFC7045].		by [RFC7045].
	3.4.3. Fragment Header for IPv6 (Protocol Number=44)		3.5.3. Fragment Header for IPv6 (Protocol Number=44)
	3.4.3.1. Uses		3.5.3.1. Uses
	This EH provides the fragmentation functionality for IPv6.		This EH provides the fragmentation functionality for IPv6.
	3.4.3.2. Specification		3.5.3.2. Specification
	This EH is specified in [RFC8200].		This EH is specified in [RFC8200].
	3.4.3.3. Specific Security Implications		3.5.3.3. Specific Security Implications
	The security implications of the Fragment Header range from Denial of		The security implications of the Fragment Header range from Denial of
	Service attacks (e.g. based on flooding a target with IPv6 fragments)		Service attacks (e.g. based on flooding a target with IPv6 fragments)
	to information leakage attacks [RFC7739].		to information leakage attacks [RFC7739].
	3.4.3.4. Operational and Interoperability Impact if Blocked		3.5.3.4. Operational and Interoperability Impact if Blocked
	Blocking packets that contain a Fragment Header will break any		Blocking packets that contain a Fragment Header will break any
	protocol that may rely on fragmentation (e.g., the DNS [RFC1034]).		protocol that may rely on fragmentation (e.g., the DNS [RFC1034]).
	However, IP fragmentation is known to introduce fragility to Internet		However, IP fragmentation is known to introduce fragility to Internet
	communication [RFC8900].		communication [RFC8900].
	3.4.3.5. Advice		3.5.3.5. Advice
	Intermediate systems should permit packets that contain a Fragment		Intermediate systems should permit packets that contain a Fragment
	Header.		Header.
	3.4.4. Encapsulating Security Payload (Protocol Number=50)		3.5.4. Encapsulating Security Payload (Protocol Number=50)
	3.4.4.1. Uses		3.5.4.1. Uses
	This EH is employed for the IPsec suite [RFC4303].		This EH is employed for the IPsec suite [RFC4303].
	3.4.4.2. Specification		3.5.4.2. Specification
	This EH is specified in [RFC4303].		This EH is specified in [RFC4303].
	3.4.4.3. Specific Security Implications		3.5.4.3. Specific Security Implications
	Besides the general implications of IPv6 EHs, this EH could be		Besides the general implications of IPv6 EHs, this EH could be
	employed to potentially perform a DoS attack at the destination		employed to potentially perform a DoS attack at the destination
	system by wasting CPU resources in validating the contents of the		system by wasting CPU resources in validating the contents of the
	packet.		packet.
	3.4.4.4. Operational and Interoperability Impact if Blocked		3.5.4.4. Operational and Interoperability Impact if Blocked
	Discarding packets that employ this EH would break IPsec deployments.		Discarding packets that employ this EH would break IPsec deployments.
	3.4.4.5. Advice		3.5.4.5. Advice
	Intermediate systems should permit packets containing the		Intermediate systems should permit packets containing the
	Encapsulating Security Payload EH.		Encapsulating Security Payload EH.
	3.4.5. Authentication Header (Protocol Number=51)		3.5.5. Authentication Header (Protocol Number=51)
	3.4.5.1. Uses		3.5.5.1. Uses
	The Authentication Header can be employed for provide authentication		The Authentication Header can be employed for provide authentication
	services in IPv4 and IPv6.		services in IPv4 and IPv6.
	3.4.5.2. Specification		3.5.5.2. Specification
	This EH is specified in [RFC4302].		This EH is specified in [RFC4302].
	3.4.5.3. Specific Security Implications		3.5.5.3. Specific Security Implications
	Besides the general implications of IPv6 EHs, this EH could be		Besides the general implications of IPv6 EHs, this EH could be
	employed to potentially perform a DoS attack at the destination		employed to potentially perform a DoS attack at the destination
	system by wasting CPU resources in validating the contents of the		system by wasting CPU resources in validating the contents of the
	packet.		packet.
	3.4.5.4. Operational and Interoperability Impact if Blocked		3.5.5.4. Operational and Interoperability Impact if Blocked
	Discarding packets that employ this EH would break IPsec deployments.		Discarding packets that employ this EH would break IPsec deployments.
	3.4.5.5. Advice		3.5.5.5. Advice
	Intermediate systems should permit packets containing an		Intermediate systems should permit packets containing an
	Authentication Header.		Authentication Header.
	3.4.6. Destination Options for IPv6 (Protocol Number=60)		3.5.6. Destination Options for IPv6 (Protocol Number=60)
	3.4.6.1. Uses		3.5.6.1. Uses
	The Destination Options header is used to carry optional information		The Destination Options header is used to carry optional information
	that needs be examined only by a packet's destination node(s).		that needs be examined only by a packet's destination node(s).
	3.4.6.2. Specification		3.5.6.2. Specification
	This EH is specified in [RFC8200]. At the time of this writing, the		This EH is specified in [RFC8200]. As of May 2022, the following
	following options have been specified for this EH:		options have been specified for this EH:
	* Type 0x00: Pad1 [RFC8200]		* Type 0x00: Pad1 [RFC8200]
	* Type 0x01: PadN [RFC8200]		* Type 0x01: PadN [RFC8200]
	* Type 0x04: Tunnel Encapsulation Limit [RFC2473]		* Type 0x04: Tunnel Encapsulation Limit [RFC2473]
			* Type 0x0F: IPv6 Performance and Diagnostic Metrics (PDM) [RFC8250]
	* Type 0x4D: (Deprecated)		* Type 0x4D: (Deprecated)
	* Type 0xC9: Home Address [RFC6275]		* Type 0xC9: Home Address [RFC6275]
	* Type 0x8A: Endpoint Identification (Deprecated)		* Type 0x8A: Endpoint Identification (Deprecated)
	[draft-ietf-nimrod-eid]		[draft-ietf-nimrod-eid]
	* Type 0x8B: ILNP Nonce [RFC6744]		* Type 0x8B: ILNP Nonce [RFC6744]
	* Type 0x8C: Line-Identification Option [RFC6788]		* Type 0x8C: Line-Identification Option [RFC6788]
	skipping to change at page 13, line 50 ¶		skipping to change at page 14, line 4 ¶
	* Type 0x3E: RFC3692-style Experiment [RFC4727]		* Type 0x3E: RFC3692-style Experiment [RFC4727]
	* Type 0x5E: RFC3692-style Experiment [RFC4727]		* Type 0x5E: RFC3692-style Experiment [RFC4727]
	* Type 0x7E: RFC3692-style Experiment [RFC4727]		* Type 0x7E: RFC3692-style Experiment [RFC4727]
	* Type 0x9E: RFC3692-style Experiment [RFC4727]		* Type 0x9E: RFC3692-style Experiment [RFC4727]
	* Type 0xBE: RFC3692-style Experiment [RFC4727]		* Type 0xBE: RFC3692-style Experiment [RFC4727]
	* Type 0xDE: RFC3692-style Experiment [RFC4727]		* Type 0xDE: RFC3692-style Experiment [RFC4727]
	* Type 0xFE: RFC3692-style Experiment [RFC4727]		* Type 0xFE: RFC3692-style Experiment [RFC4727]
	3.4.6.3. Specific Security Implications		3.5.6.3. Specific Security Implications
	No security implications are known, other than the general		No security implications are known, other than the general
	implications of IPv6 EHs. For a discussion of possible security		implications of IPv6 EHs. For a discussion of possible security
	implications of specific options specified for the DO header, please		implications of specific options specified for the DO header, please
	see the Section 4.3.		see the Section 4.4.
	3.4.6.4. Operational and Interoperability Impact if Blocked		3.5.6.4. Operational and Interoperability Impact if Blocked
	Discarding packets that contain a Destination Options header would		Discarding packets that contain a Destination Options header would
	break protocols that rely on this EH type for conveying information,		break protocols that rely on this EH type for conveying information,
	including protocols such as ILNP [RFC6740] and Mobile IPv6 [RFC6275],		including protocols such as ILNP [RFC6740] and Mobile IPv6 [RFC6275],
	and IPv6 tunnels that employ the Tunnel Encapsulation Limit option.		and IPv6 tunnels that employ the Tunnel Encapsulation Limit option.
	3.4.6.5. Advice		3.5.6.5. Advice
	Intermediate systems should permit packets that contain a Destination		Intermediate systems should permit packets that contain a Destination
	Options Header.		Options Header.
	3.4.7. Mobility Header (Protocol Number=135)		3.5.7. Mobility Header (Protocol Number=135)
	3.4.7.1. Uses		3.5.7.1. Uses
	The Mobility Header is an EH used by mobile nodes, correspondent		The Mobility Header is an EH used by mobile nodes, correspondent
	nodes, and home agents in all messaging related to the creation and		nodes, and home agents in all messaging related to the creation and
	management of bindings in Mobile IPv6.		management of bindings in Mobile IPv6.
	3.4.7.2. Specification		3.5.7.2. Specification
	This EH is specified in [RFC6275].		This EH is specified in [RFC6275].
	3.4.7.3. Specific Security Implications		3.5.7.3. Specific Security Implications
	A thorough security assessment of the security implications of the		A thorough security assessment of the security implications of the
	Mobility Header and related mechanisms can be found in Section 15 of		Mobility Header and related mechanisms can be found in Section 15 of
	[RFC6275].		[RFC6275].
	3.4.7.4. Operational and Interoperability Impact if Blocked		3.5.7.4. Operational and Interoperability Impact if Blocked
	Discarding packets containing this EH would break Mobile IPv6.		Discarding packets containing this EH would break Mobile IPv6.
	3.4.7.5. Advice		3.5.7.5. Advice
	Intermediate systems should permit packets containing this EH.		Intermediate systems should permit packets containing this EH.
	3.4.8. Host Identity Protocol (Protocol Number=139)		3.5.8. Host Identity Protocol (Protocol Number=139)
	3.4.8.1. Uses		3.5.8.1. Uses
	This EH is employed with the Host Identity Protocol (HIP), an		This EH is employed with the Host Identity Protocol (HIP), a protocol
	experimental protocol that allows consenting hosts to securely		that allows consenting hosts to securely establish and maintain
	establish and maintain shared IP-layer state, allowing separation of		shared IP-layer state, allowing separation of the identifier and
	the identifier and locator roles of IP addresses, thereby enabling		locator roles of IP addresses, thereby enabling continuity of
	continuity of communications across IP address changes.		communications across IP address changes.
	3.4.8.2. Specification		3.5.8.2. Specification
	This EH is specified in [RFC7401].		This EH is specified in [RFC7401].
	3.4.8.3. Specific Security Implications		3.5.8.3. Specific Security Implications
	The security implications of the HIP header are discussed in detail		The security implications of the HIP header are discussed in detail
	in Section 8 of [RFC6275].		in Section 8 of [RFC6275].
	3.4.8.4. Operational and Interoperability Impact if Blocked		3.5.8.4. Operational and Interoperability Impact if Blocked
	Discarding packets that contain the Host Identity Protocol would		Discarding packets that contain the Host Identity Protocol would
	break HIP deployments.		break HIP deployments.
	3.4.8.5. Advice		3.5.8.5. Advice
	Intermediate systems should permit packets that contain a Host		Intermediate systems should permit packets that contain a Host
	Identity Protocol EH.		Identity Protocol EH.
	3.4.9. Shim6 Protocol (Protocol Number=140)		3.5.9. Shim6 Protocol (Protocol Number=140)
	3.4.9.1. Uses		3.5.9.1. Uses
	This EH is employed by the Shim6 [RFC5533] Protocol.		This EH is employed by the Shim6 [RFC5533] Protocol.
	3.4.9.2. Specification		3.5.9.2. Specification
	This EH is specified in [RFC5533].		This EH is specified in [RFC5533].
	3.4.9.3. Specific Security Implications		3.5.9.3. Specific Security Implications
	The specific security implications are discussed in detail in		The specific security implications are discussed in detail in
	Section 16 of [RFC5533].		Section 16 of [RFC5533].
	3.4.9.4. Operational and Interoperability Impact if Blocked		3.5.9.4. Operational and Interoperability Impact if Blocked
	Discarding packets that contain this EH will break Shim6.		Discarding packets that contain this EH will break Shim6.
	3.4.9.5. Advice		3.5.9.5. Advice
	Intermediate systems should permit packets containing this EH.		Intermediate systems should permit packets containing this EH.
	3.4.10. Use for experimentation and testing (Protocol Numbers=253 and		3.5.10. Use for experimentation and testing (Protocol Numbers=253 and
	254)		254)
	3.4.10.1. Uses		3.5.10.1. Uses
	These IPv6 EHs are employed for performing RFC3692-Style experiments		These IPv6 EHs are employed for performing RFC3692-Style experiments
	(see [RFC3692] for details).		(see [RFC3692] for details).
	3.4.10.2. Specification		3.5.10.2. Specification
	These EHs are specified in [RFC3692] and [RFC4727].		These EHs are specified in [RFC3692] and [RFC4727].
	3.4.10.3. Specific Security Implications		3.5.10.3. Specific Security Implications
	The security implications of these EHs will depend on their specific		The security implications of these EHs will depend on their specific
	use.		use.
	3.4.10.4. Operational and Interoperability Impact if Blocked		3.5.10.4. Operational and Interoperability Impact if Blocked
	For obvious reasons, discarding packets that contain these EHs limits		For obvious reasons, discarding packets that contain these EHs limits
	the ability to perform legitimate experiments across IPv6 routers.		the ability to perform legitimate experiments across IPv6 routers.
	3.4.10.5. Advice		3.5.10.5. Advice
	Operators should determine according to their own circumstances		Operators should determine according to their own circumstances
	whether to discard packets containing these EHs.		whether to discard packets containing these EHs.
	3.5. Advice on the Handling of Packets with Unknown IPv6 Extension		3.6. Advice on the Handling of Packets with Unknown IPv6 Extension
	Headers		Headers
	We refer to IPv6 EHs that have not been assigned an Internet Protocol		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		Number by IANA (and marked as such) in [IANA-PROTOCOLS] as "unknown
	IPv6 extension headers" ("unknown IPv6 EHs").		IPv6 extension headers" ("unknown IPv6 EHs").
	3.5.1. Uses		3.6.1. Uses
	New IPv6 EHs may be specified as part of future extensions to the		New IPv6 EHs may be specified as part of future extensions to the
	IPv6 protocol.		IPv6 protocol.
	Since IPv6 EHs and Upper-layer protocols employ the same namespace,		Since IPv6 EHs and Upper-layer protocols employ the same namespace,
	it is impossible to tell whether an unknown "Internet Protocol		it is impossible to tell whether an unknown "Internet Protocol
	Number" is being employed for an IPv6 EH or an Upper-Layer protocol.		Number" is being employed for an IPv6 EH or an Upper-Layer protocol.
	3.5.2. Specification		3.6.2. Specification
	The processing of unknown IPv6 EHs is specified in [RFC7045].		The processing of unknown IPv6 EHs is specified in [RFC7045].
	3.5.3. Specific Security Implications		3.6.3. Specific Security Implications
	For obvious reasons, it is impossible to determine specific security		For obvious reasons, it is impossible to determine specific security
	implications of unknown IPv6 EHs.		implications of unknown IPv6 EHs.
	3.5.4. Operational and Interoperability Impact if Blocked		3.6.4. Operational and Interoperability Impact if Blocked
	As noted in [RFC7045], discarding unknown IPv6 EHs may slow down the		As noted in [RFC7045], discarding unknown IPv6 EHs may slow down the
	deployment of new IPv6 EHs and transport protocols. The		deployment of new IPv6 EHs and transport protocols. The
	corresponding IANA registry ([IANA-PROTOCOLS]) should be monitored		corresponding IANA registry ([IANA-PROTOCOLS]) should be monitored
	such that filtering rules are updated as new IPv6 EHs are		such that filtering rules are updated as new IPv6 EHs are
	standardized.		standardized.
	We note that since IPv6 EHs and upper-layer protocols share the same		We note that since IPv6 EHs and upper-layer protocols share the same
	numbering space, discarding unknown IPv6 EHs may result in packets		numbering space, discarding unknown IPv6 EHs may result in packets
	encapsulating unknown upper-layer protocols being discarded.		encapsulating unknown upper-layer protocols being discarded.
	3.5.5. Advice		3.6.5. Advice
	Operators should determine according to their own circumstances		Operators should determine according to their own circumstances
	whether to discard packets containing unknown IPv6 EHs.		whether to discard packets containing unknown IPv6 EHs.
	4. IPv6 Options		4. IPv6 Options
	4.1. General Discussion		4.1. General Discussion
	The following subsections describe specific security implications of		The following subsections describe specific security implications of
	different IPv6 options, and provide advice regarding filtering		different IPv6 options, and provide advice regarding filtering
	skipping to change at page 18, line 5 ¶		skipping to change at page 18, line 5 ¶
	The general security implications of IPv6 options are closely related		The general security implications of IPv6 options are closely related
	to those discussed in Section 3.2 for IPv6 EHs. Essentially, packets		to those discussed in Section 3.2 for IPv6 EHs. Essentially, packets
	that contain IPv6 options might need to be processed by an IPv6		that contain IPv6 options might need to be processed by an IPv6
	router's general-purpose CPU,and hence could present a DDoS risk to		router's general-purpose CPU,and hence could present a DDoS risk to
	that router's general-purpose CPU (and thus to the router itself).		that router's general-purpose CPU (and thus to the router itself).
	For some architectures, a possible mitigation would be to rate-limit		For some architectures, a possible mitigation would be to rate-limit
	the packets that are to be processed by the general-purpose CPU (see		the packets that are to be processed by the general-purpose CPU (see
	e.g. [Cisco-EH]).		e.g. [Cisco-EH]).
	4.3. Advice on the Handling of Packets with Specific IPv6 Options		4.3. 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.
			+===============================+======================+===========+
			| 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=0C2) | Permit based on | Section |
			| | needed functionality | 4.4.16 |
			+-------------------------------+----------------------+-----------+
			| RPL Option (Type=0x63) | Drop in non-RPL | Section |
			| | routers | 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		The following subsections contain a description of each of the IPv6
	options that have so far been specified, a summary of the security		options that have so far been specified, a summary of the security
	implications of each of such options, a discussion of possible		implications of each of such options, a discussion of possible
	interoperability implications if packets containing such options are		interoperability implications if packets containing such options are
	discarded, and specific advice regarding whether packets containing		discarded, and specific advice regarding whether packets containing
	these options should be permitted.		these options should be permitted.
	4.3.1. Pad1 (Type=0x00)		4.4.1. Pad1 (Type=0x00)
	4.3.1.1. Uses		4.4.1.1. Uses
	This option is used when necessary to align subsequent options and to		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.		pad out the containing header to a multiple of 8 octets in length.
	4.3.1.2. Specification		4.4.1.2. Specification
	This option is specified in [RFC8200].		This option is specified in [RFC8200].
	4.3.1.3. Specific Security Implications		4.4.1.3. Specific Security Implications
	None.		None.
	4.3.1.4. Operational and Interoperability Impact if Blocked		4.4.1.4. Operational and Interoperability Impact if Blocked
	Discarding packets that contain this option would potentially break		Discarding packets that contain this option would potentially break
	any protocol that relies on IPv6 options.		any protocol that relies on IPv6 options.
	4.3.1.5. Advice		4.4.1.5. Advice
	Intermediate systems should not discard packets based on the presence		Intermediate systems should not discard packets based on the presence
	of this option.		of this option.
	4.3.2. PadN (Type=0x01)		4.4.2. PadN (Type=0x01)
	4.3.2.1. Uses		4.4.2.1. Uses
	This option is used when necessary to align subsequent options and to		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.		pad out the containing header to a multiple of 8 octets in length.
	4.3.2.2. Specification		4.4.2.2. Specification
	This option is specified in [RFC8200].		This option is specified in [RFC8200].
	4.3.2.3. Specific Security Implications		4.4.2.3. Specific Security Implications
	Because of the possible size of this option, it could be leveraged as		Because of the possible size of this option, it could be leveraged as
	a large-bandwidth covert channel.		a large-bandwidth covert channel.
	4.3.2.4. Operational and Interoperability Impact if Blocked		4.4.2.4. Operational and Interoperability Impact if Blocked
	Discarding packets that contain this option would potentially break		Discarding packets that contain this option would potentially break
	any protocol that relies on IPv6 options.		any protocol that relies on IPv6 options.
	4.3.2.5. Advice		4.4.2.5. Advice
	Intermediate systems should not discard IPv6 packets based on the		Intermediate systems should not discard IPv6 packets based on the
	presence of this option.		presence of this option.
	4.3.3. Jumbo Payload (Type=0XC2)		4.4.3. Tunnel Encapsulation Limit (Type=0x04)
	4.3.3.1. Uses
	The Jumbo payload option provides the means of specifying payloads
	larger than 65535 bytes.
	4.3.3.2. Specification
	This option is specified in [RFC2675].
	4.3.3.3. Specific Security Implications
	There are no specific issues arising from this option, except for
	improper validity checks of the option and associated packet lengths.
	4.3.3.4. Operational and Interoperability Impact if Blocked
	Discarding packets based on the presence of this option will cause
	IPv6 jumbograms to be discarded.
	4.3.3.5. Advice
	An operator should permit this option only in specific scenarios in
	which support for IPv6 jumbograms is desired.
	4.3.4. RPL Option (Type=0x63)
	4.3.4.1. Uses
	The RPL Option provides a mechanism to include routing information
	with each datagram that an RPL router forwards.
	4.3.4.2. Specification
	This option was originally specified in [RFC6553]. It has been
	deprecated by [RFC9008].
	4.3.4.3. Specific Security Implications
	Those described in [RFC9008].
	4.3.4.4. Operational and Interoperability Impact if Blocked
	This option is meant to be employed within an RPL instance. As a
	result, discarding packets based on the presence of this option
	outside of an RPL instance will not result in interoperability
	implications.
	4.3.4.5. Advice
	Non-RPL routers should discard packets that contain an RPL option.
	4.3.5. RPL Option (Type=0x23)
	4.3.5.1. Uses
	The RPL Option provides a mechanism to include routing information
	with each datagram that an RPL router forwards.
	4.3.5.2. Specification
	This option is specified in [RFC9008].
	4.3.5.3. Specific Security Implications
	Those described in [RFC9008].
	4.3.5.4. Operational and Interoperability Impact if Blocked
	This option can survive outside of an RPL instance. As a result,
	discarding packets based on the presence of this option would break
	some use cases for RPL (see [RFC9008]).
	4.3.5.5. Advice
	Intermediate systems should not discard IPv6 packets based on the
	presence of this option.
	4.3.6. Tunnel Encapsulation Limit (Type=0x04)		4.4.3.1. Uses
	4.3.6.1. Uses
	The Tunnel Encapsulation Limit option can be employed to specify how		The Tunnel Encapsulation Limit option can be employed to specify how
	many further levels of nesting the packet is permitted to undergo.		many further levels of nesting the packet is permitted to undergo.
	4.3.6.2. Specification		4.4.3.2. Specification
	This option is specified in [RFC2473].		This option is specified in [RFC2473].
	4.3.6.3. Specific Security Implications		4.4.3.3. Specific Security Implications
	Those described in [RFC2473].		Those described in [RFC2473].
	4.3.6.4. Operational and Interoperability Impact if Blocked		4.4.3.4. Operational and Interoperability Impact if Blocked
	Discarding packets based on the presence of this option could result		Discarding packets based on the presence of this option could result
	in tunnel traffic being discarded.		in tunnel traffic being discarded.
	4.3.6.5. Advice		4.4.3.5. Advice
	Intermediate systems should not discard packets based on the presence		Intermediate systems should not discard packets based on the presence
	of this option.		of this option.
	4.3.7. Router Alert (Type=0x05)		4.4.4. Router Alert (Type=0x05)
	4.3.7.1. Uses		4.4.4.1. Uses
	The Router Alert option [RFC2711] is employed by a number of		The Router Alert option [RFC2711] is employed by a number of
	protocols, including the Resource reSerVation Protocol (RSVP)		protocols, including the Resource reSerVation Protocol (RSVP)
	[RFC2205], Multicast Listener Discovery (MLD) [RFC2710] [RFC3810],		[RFC2205], Multicast Listener Discovery (MLD) [RFC2710] [RFC3810],
	Multicast Router Discovery (MRD) [RFC4286], and General Internet		Multicast Router Discovery (MRD) [RFC4286], and General Internet
	Signaling Transport (GIST) [RFC5971]. Its usage is discussed in		Signaling Transport (GIST) [RFC5971]. Its usage is discussed in
	detail in [RFC6398].		detail in [RFC6398].
	4.3.7.2. Specification		4.4.4.2. Specification
	This option is specified in [RFC2711].		This option is specified in [RFC2711].
	4.3.7.3. Specific Security Implications		4.4.4.3. Specific Security Implications
	Since this option causes the contents of the packet to be inspected		Since this option causes the contents of the packet to be inspected
	by the handling device, this option could be leveraged for performing		by the handling device, this option could be leveraged for performing
	DoS attacks. The security implications of the Router Alert option		DoS attacks. The security implications of the Router Alert option
	are discussed in detail in [RFC6398].		are discussed in detail in [RFC6398].
	4.3.7.4. Operational and Interoperability Impact if Blocked		4.4.4.4. Operational and Interoperability Impact if Blocked
	Discarding packets that contain this option would break any protocols		Discarding packets that contain this option would break any protocols
	that rely on them, such as RSVP and multicast deployments. Please		that rely on them, such as RSVP and multicast deployments. Please
	see Section 4.3.7.3 for further details.		see Section 4.4.4.3 for further details.
	4.3.7.5. Advice		4.4.4.5. Advice
	Packets containing this option should be permitted in environments		Packets containing this option should be permitted in environments
	where support for RSVP, multicast routing, or similar protocols is		where support for RSVP, multicast routing, or similar protocols is
	desired.		desired.
	4.3.8. Quick-Start (Type=0x26)		4.4.5. CALIPSO (Type=0x07)
	4.3.8.1. 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].
	4.3.8.2. Specification
	This option is specified in [RFC4782], on the "Experimental" track.
	4.3.8.3. 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.
	4.3.8.4. Operational and Interoperability Impact if Blocked
	The Quick-Start functionality would be disabled, and additional
	delays in TCP's connection establishment (for example) could be
	introduced. (Please see 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].
	4.3.8.5. Advice
	Intermediate systems should not discard IPv6 packets based on the
	presence of this option.
	4.3.9. CALIPSO (Type=0x07)
	4.3.9.1. Uses		4.4.5.1. Uses
	This option is used for encoding explicit packet Sensitivity Labels		This option is used for encoding explicit packet Sensitivity Labels
	on IPv6 packets. It is intended for use only within Multi-Level		on IPv6 packets. It is intended for use only within Multi-Level
	Secure (MLS) networking environments that are both trusted and		Secure (MLS) networking environments that are both trusted and
	trustworthy.		trustworthy.
	4.3.9.2. Specification		4.4.5.2. Specification
	This option is specified in [RFC5570].		This option is specified in [RFC5570].
	4.3.9.3. Specific Security Implications		4.4.5.3. Specific Security Implications
	Presence of this option in a packet does not by itself create any		Presence of this option in a packet does not by itself create any
	specific new threat. Packets with this option ought not normally be		specific new threat. Packets with this option ought not normally be
	seen on the global public Internet.		seen on the global public Internet.
	4.3.9.4. Operational and Interoperability Impact if Blocked		4.4.5.4. Operational and Interoperability Impact if Blocked
	If packets with this option are discarded or if the option is		If packets with this option are discarded or if the option is
	stripped from the packet during transmission from source to		stripped from the packet during transmission from source to
	destination, then the packet itself is likely to be discarded by the		destination, then the packet itself is likely to be discarded by the
	receiver because it is not properly labeled. In some cases, the		receiver because it is not properly labeled. In some cases, the
	receiver might receive the packet but associate an incorrect		receiver might receive the packet but associate an incorrect
	sensitivity label with the received data from the packet whose		sensitivity label with the received data from the packet whose
	CALIPSO was stripped by an intermediate router or firewall.		CALIPSO was stripped by a middle-box (such as a packet-scrubber).
	Associating an incorrect sensitivity label can cause the received		Associating an incorrect sensitivity label can cause the received
	information either to be handled as more sensitive than it really is		information either to be handled as more sensitive than it really is
	("upgrading") or as less sensitive than it really is ("downgrading"),		("upgrading") or as less sensitive than it really is ("downgrading"),
	either of which is problematic. As noted in [RFC5570], IPsec		either of which is problematic. As noted in [RFC5570], IPsec
	[RFC4301] [RFC4302] [RFC4303] can be employed to protect the CALIPSO		[RFC4301] [RFC4302] [RFC4303] can be employed to protect the CALIPSO
	option.		option.
	4.3.9.5. Advice		4.4.5.5. Advice
	Recommendations for handling the CALIPSO option depend on the		Recommendations for handling the CALIPSO option depend on the
	deployment environment, rather than whether an intermediate system		deployment environment, rather than whether an intermediate system
	happens to be deployed as a transit device (e.g., IPv6 transit		happens to be deployed as a transit device (e.g., IPv6 transit
	router).		router).
	Explicit configuration is the only method via which an intermediate		Explicit configuration is the only method via which an intermediate
	system can know whether that particular intermediate system has been		system can know whether that particular intermediate system has been
	deployed within a Multi-Level Secure (MLS) environment. In many		deployed within a Multi-Level Secure (MLS) environment. In many
	cases, ordinary commercial intermediate systems (e.g., IPv6 routers		cases, ordinary commercial intermediate systems (e.g., IPv6 routers
	skipping to change at page 24, line 42 ¶		skipping to change at page 23, line 27 ¶
	configuration options (a) and (b) from the preceding paragraph and		configuration options (a) and (b) from the preceding paragraph and
	also a third configuration option (c) to process packets containing a		also a third configuration option (c) to process packets containing a
	CALIPSO option as per [RFC5570]. When deployed in non-MLS		CALIPSO option as per [RFC5570]. When deployed in non-MLS
	environments, such intermediate systems should have this		environments, such intermediate systems should have this
	configuration option set to (a) above. When deployed in MLS		configuration option set to (a) above. When deployed in MLS
	environments, such intermediate systems should have this set to (c).		environments, such intermediate systems should have this set to (c).
	The default setting for this configuration option MAY be set to (a)		The default setting for this configuration option MAY be set to (a)
	above, because MLS environments are much less common than non-MLS		above, because MLS environments are much less common than non-MLS
	environments.		environments.
	4.3.10. SMF_DPD (Type=0x08)		4.4.6. SMF_DPD (Type=0x08)
	4.3.10.1. Uses		4.4.6.1. Uses
	This option is employed in the (experimental) Simplified Multicast		This option is employed in the (experimental) Simplified Multicast
	Forwarding (SMF) for unique packet identification for IPv6 I-DPD, and		Forwarding (SMF) for unique packet identification for IPv6 I-DPD, and
	as a mechanism to guarantee non-collision of hash values for		as a mechanism to guarantee non-collision of hash values for
	different packets when H-DPD is used.		different packets when H-DPD is used.
	4.3.10.2. Specification		4.4.6.2. Specification
	This option is specified in [RFC6621].		This option is specified in [RFC6621].
	4.3.10.3. Specific Security Implications		4.4.6.3. Specific Security Implications
	None. The use of transient numeric identifiers is subject to the		None. The use of transient numeric identifiers is subject to the
	security and privacy considerations discussed in		security and privacy considerations discussed in
	[I-D.irtf-pearg-numeric-ids-generation].		[I-D.irtf-pearg-numeric-ids-generation].
	4.3.10.4. Operational and Interoperability Impact if Blocked		4.4.6.4. Operational and Interoperability Impact if Blocked
	Dropping packets containing this option within a MANET domain would		Dropping packets containing this option within a MANET domain would
	break SMF. However, dropping such packets at the border of such		break SMF. However, dropping such packets at the border of such
	domain would have no negative impact.		domain would have no negative impact.
	4.3.10.5. Advice		4.4.6.5. Advice
	Intermediate systems that are not within a MANET domain should		Intermediate systems that are not within a MANET domain should
	discard packets that contain this option.		discard packets that contain this option.
	4.3.11. Home Address (Type=0xC9)		4.4.7. PDM (Type=0x0F)
	4.3.11.1. Uses		4.4.7.1. Uses
	The Home Address option is used by a Mobile IPv6 node while away from		This option is employed to convey sequence numbers and timing
	home, to inform the recipient of the mobile node's home address.		information in IPv6 packets as a basis for measurements.
	4.3.11.2. Specification		4.4.7.2. Specification
	This option is specified in [RFC6275].		This option is specified in [RFC8250].
	4.3.11.3. Specific Security Implications		4.4.7.3. Specific Security Implications
	No (known) additional security implications than those described in		Those specified in [RFC8250]. Additionally, since the options
	[RFC6275].		employs transient numeric identifiers, implementations may be subject
			to the issues discussed in [I-D.irtf-pearg-numeric-ids-generation].
	4.3.11.4. Operational and Interoperability Impact if Blocked		4.4.7.4. Operational and Interoperability Impact if Blocked
	Discarding IPv6 packets based on the presence of this option will		Dropping packets containing this option will result in negative
	break Mobile IPv6.		interoperaiblity implications for traffic employing this option as a
			basis for measurements.
	4.3.11.5. Advice		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
			with each datagram that an RPL router forwards.
			4.4.8.2. Specification
			This option is specified in [RFC9008].
			4.4.8.3. Specific Security Implications
			Those described in [RFC9008].
			4.4.8.4. Operational and Interoperability Impact if Blocked
			This option can survive outside of an 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		Intermediate systems should not discard IPv6 packets based on the
	presence of this option.		presence of this option.
	4.3.12. Endpoint Identification (Type=0x8A)		4.4.9. Quick-Start (Type=0x26)
	4.3.12.1. Uses		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
			The Quick-Start functionality would be disabled, and additional
			delays in TCP's connection establishment (for example) could be
			introduced. (Please see 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, and 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
			with each datagram that an 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
			Those described in [RFC9008].
			4.4.11.4. Operational and Interoperability Impact if Blocked
			This option is meant to be employed within an RPL instance. As a
			result, discarding packets based on the presence of this option
			outside of an RPL instance will not result in interoperability
			implications.
			4.4.11.5. Advice
			Non-RPL routers should discard packets that contain an 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), that 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 Option headers.
			4.4.12.3. Specific Security Implications
			Those described 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 Multicast Protocol for Low power and Lossy Networks
			(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, 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		The Endpoint Identification option was meant to be used with the
	Nimrod routing architecture [NIMROD-DOC], but has never seen		Nimrod routing architecture [NIMROD-DOC], but has never seen
	widespread deployment.		widespread deployment.
	4.3.12.2. Specification		4.4.13.2. Specification
	This option is specified in [NIMROD-DOC].		This option is specified in [NIMROD-DOC].
	4.3.12.3. Specific Security Implications		4.4.13.3. Specific Security Implications
	Undetermined.		Undetermined.
	4.3.12.4. Operational and Interoperability Impact if Blocked		4.4.13.4. Operational and Interoperability Impact if Blocked
	None.		None.
	4.3.12.5. Advice		4.4.13.5. Advice
	Intermediate systems should discard packets that contain this option.		Intermediate systems should discard packets that contain this option.
	4.3.13. ILNP Nonce (Type=0x8B)		4.4.14. ILNP Nonce (Type=0x8B)
	4.3.13.1. Uses		4.4.14.1. Uses
	This option is employed by Identifier-Locator Network Protocol for		This option is employed by Identifier-Locator Network Protocol for
	IPv6 (ILNPv6) for providing protection against off-path attacks for		IPv6 (ILNPv6) for providing protection against off-path attacks for
	packets when ILNPv6 is in use, and as a signal during initial		packets when ILNPv6 is in use, and as a signal during initial
	network-layer session creation that ILNPv6 is proposed for use with		network-layer session creation that ILNPv6 is proposed for use with
	this network-layer session, rather than classic IPv6.		this network-layer session, rather than classic IPv6.
	4.3.13.2. Specification		4.4.14.2. Specification
	This option is specified in [RFC6744].		This option is specified in [RFC6744].
	4.3.13.3. Specific Security Implications		4.4.14.3. Specific Security Implications
	Those described in [RFC6744].		Those described in [RFC6744].
	4.3.13.4. Operational and Interoperability Impact if Blocked		4.4.14.4. Operational and Interoperability Impact if Blocked
	Discarding packets that contain this option will break INLPv6		Discarding packets that contain this option will break INLPv6
	deployments.		deployments.
	4.3.13.5. Advice		4.4.14.5. Advice
	Intermediate systems should not discard packets based on the presence		Intermediate systems should not discard packets based on the presence
	of this option.		of this option.
	4.3.14. Line-Identification Option (Type=0x8C)		4.4.15. Line-Identification Option (Type=0x8C)
	4.3.14.1. Uses		4.4.15.1. Uses
	This option is used by an Edge Router to identify the subscriber		This option is used by an Edge Router to identify the subscriber
	premises in scenarios where several subscriber premises may be		premises in scenarios where several subscriber premises may be
	logically connected to the same interface of an Edge Router.		logically connected to the same interface of an Edge Router.
	4.3.14.2. Specification		4.4.15.2. Specification
	This option is specified in [RFC6788].		This option is specified in [RFC6788].
	4.3.14.3. Specific Security Implications		4.4.15.3. Specific Security Implications
	Those described in [RFC6788].		Those described in [RFC6788].
	4.3.14.4. Operational and Interoperability Impact if Blocked		4.4.15.4. Operational and Interoperability Impact if Blocked
	Since this option is meant to be employed in Router Solicitation		Since this option is meant to be employed in Router Solicitation
	messages, discarding packets based on the presence of this option at		messages, discarding packets based on the presence of this option at
	intermediate systems will result in no interoperability implications.		intermediate systems will result in no interoperability implications.
	4.3.14.5. Advice		4.4.15.5. Advice
	Intermediate devices should discard packets that contain this option.		Intermediate devices should discard packets that contain this option.
	4.3.15. Deprecated (Type=0x4D)		4.4.16. Jumbo Payload (Type=0XC2)
	4.3.15.1. Uses		4.4.16.1. Uses
	No information has been found about this option type.		The Jumbo payload option provides the means of specifying payloads
			larger than 65535 bytes.
	4.3.15.2. Specification		4.4.16.2. Specification
	No information has been found about this option type.		This option is specified in [RFC2675].
	4.3.15.3. Specific Security Implications		4.4.16.3. Specific Security Implications
	No information has been found about this option type, and hence it		There are no specific issues arising from this option, except for
	has been impossible to perform the corresponding security assessment.		improper validity checks of the option and associated packet lengths.
	4.3.15.4. Operational and Interoperability Impact if Blocked		4.4.16.4. Operational and Interoperability Impact if Blocked
	Unknown.		Discarding packets based on the presence of this option will cause
			IPv6 jumbograms to be discarded.
	4.3.15.5. Advice		4.4.16.5. Advice
	Intermediate systems should discard packets that contain this option.		An operator should permit this option only in specific scenarios in
			which support for IPv6 jumbograms is desired.
	4.3.16. MPL Option (Type=0x6D)		4.4.17. Home Address (Type=0xC9)
	4.3.16.1. Uses		4.4.17.1. Uses
	This option is used with the Multicast Protocol for Low power and		The Home Address option is used by a Mobile IPv6 node while away from
	Lossy Networks (MPL), that provides IPv6 multicast forwarding in		home, to inform the recipient of the mobile node's home address.
	constrained networks.
	4.3.16.2. Specification		4.4.17.2. Specification
	This option is specified in [RFC7731], and is meant to be included		This option is specified in [RFC6275].
	only in Hop-by-Hop Option headers.
	4.3.16.3. Specific Security Implications		4.4.17.3. Specific Security Implications
	Those described in [RFC7731].		No (known) additional security implications than those described in
			[RFC6275].
	4.3.16.4. Operational and Interoperability Impact if Blocked		4.4.17.4. Operational and Interoperability Impact if Blocked
	Dropping packets that contain an MPL option within an MPL network		Discarding IPv6 packets based on the presence of this option will
	would break the Multicast Protocol for Low power and Lossy Networks		break Mobile IPv6.
	(MPL). However, dropping such packets at the border of such networks
	will have no negative impact.
	4.3.16.5. Advice		4.4.17.5. Advice
	Intermediate systems should not discard packets based on the presence		Intermediate systems should not discard IPv6 packets based on the
	of this option. However, since this option has been specified for		presence of this option.
	the Hop-by-Hop Options, such systems should consider the discussion
	in Section 3.4.1.
	4.3.17. IP_DFF (Type=0xEE)		4.4.18. IP_DFF (Type=0xEE)
	4.3.17.1. Uses		4.4.18.1. Uses
	This option is employed with the (Experimental) Depth-First		This option is employed with the (Experimental) Depth-First
	Forwarding (DFF) in Unreliable Networks.		Forwarding (DFF) in Unreliable Networks.
	4.3.17.2. Specification		4.4.18.2. Specification
	This option is specified in [RFC6971].		This option is specified in [RFC6971].
	4.3.17.3. Specific Security Implications		4.4.18.3. Specific Security Implications
	Those specified in [RFC6971].		Those specified in [RFC6971].
	4.3.17.4. Operational and Interoperability Impact if Blocked		4.4.18.4. Operational and Interoperability Impact if Blocked
	Dropping packets containing this option within a routing domain that		Dropping packets containing this option within a routing domain that
	is running DFF would break DFF. However, dropping such packets at		is running DFF would break DFF. However, dropping such packets at
	the border of such domains will have no security implications.		the border of such domains will have no security implications.
	4.3.17.5. Advice		4.4.18.5. Advice
	Intermediate systems that do not operate within a routing domain that		Intermediate systems that do not operate within a routing domain that
	is running DFF should discard packets containing this option.		is running DFF should discard packets containing this option.
	4.3.18. RFC3692-style Experiment (Types = 0x1E, 0x3E, 0x5E, 0x7E, 0x9E,		4.4.19. RFC3692-style Experiment (Types = 0x1E, 0x3E, 0x5E, 0x7E, 0x9E,
	0xBE, 0xDE, 0xFE)		0xBE, 0xDE, 0xFE)
	4.3.18.1. Uses		4.4.19.1. Uses
	These options can be employed for performing RFC3692-style		These options can be employed for performing RFC3692-style
	experiments. It is only appropriate to use these values in		experiments. It is only appropriate to use these values in
	explicitly configured experiments; they must not be shipped as		explicitly configured experiments; they must not be shipped as
	defaults in implementations.		defaults in implementations.
	4.3.18.2. Specification		4.4.19.2. Specification
	Specified in RFC 4727 [RFC4727] in the context of RFC3692-style		Specified in RFC 4727 [RFC4727] in the context of RFC3692-style
	experiments.		experiments.
	4.3.18.3. Specific Security Implications		4.4.19.3. Specific Security Implications
	The specific security implications will depend on the specific use of		The specific security implications will depend on the specific use of
	these options.		these options.
	4.3.18.4. Operational and Interoperability Impact if Blocked		4.4.19.4. Operational and Interoperability Impact if Blocked
	For obvious reasons, discarding packets that contain these options		For obvious reasons, discarding packets that contain these options
	limits the ability to perform legitimate experiments across IPv6		limits the ability to perform legitimate experiments across IPv6
	routers.		routers.
	4.3.18.5. Advice		4.4.19.5. Advice
	Operators should determine according to their own circumstances		Operators should determine according to their own circumstances
	whether to discard packets containing these IPv6 options.		whether to discard packets containing these IPv6 options.
	4.4. Advice on the handling of Packets with Unknown 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		We refer to IPv6 options that have not been assigned an IPv6 option
	type in the corresponding registry ([IANA-IPV6-PARAM]) as "unknown		type in the corresponding registry ([IANA-IPV6-PARAM]) as "unknown
	IPv6 options".		IPv6 options".
	4.4.1. Uses		4.5.1. Uses
	New IPv6 options may be specified as part of future protocol work.		New IPv6 options may be specified as part of future protocol work.
	4.4.2. Specification		4.5.2. Specification
	The processing of unknown IPv6 options is specified in [RFC8200].		The processing of unknown IPv6 options is specified in [RFC8200].
	4.4.3. Specific Security Implications		4.5.3. Specific Security Implications
	For obvious reasons, it is impossible to determine specific security		For obvious reasons, it is impossible to determine specific security
	implications of unknown IPv6 options.		implications of unknown IPv6 options.
	4.4.4. Operational and Interoperability Impact if Blocked		4.5.4. Operational and Interoperability Impact if Blocked
	Discarding unknown IPv6 options may slow down the deployment of new		Discarding unknown IPv6 options may slow down the deployment of new
	IPv6 options. As noted in [draft-gont-6man-ipv6-opt-transmit], the		IPv6 options. As noted in [draft-gont-6man-ipv6-opt-transmit], the
	corresponding IANA registry ([IANA-IPV6-PARAM] should be monitored		corresponding IANA registry ([IANA-IPV6-PARAM] should be monitored
	such that IPv6 option filtering rules are updated as new IPv6 options		such that IPv6 option filtering rules are updated as new IPv6 options
	are standardized.		are standardized.
	4.4.5. Advice		4.5.5. Advice
	Operators should determine according to their own circumstances		Operators should determine according to their own circumstances
	whether to discard packets containing unknown IPv6 options.		whether to discard packets containing unknown IPv6 options.
	5. IANA Considerations		5. IANA Considerations
	This document has no actions for IANA.		This document has no actions for IANA.
	6. Privacy Considerations		6. Privacy Considerations
	skipping to change at page 31, line 14 ¶		skipping to change at page 33, line 5 ¶
	7. Security Considerations		7. Security Considerations
	This document provides advice on the filtering of IPv6 packets that		This document provides advice on the filtering of IPv6 packets that
	contain IPv6 EHs (and possibly IPv6 options) at IPv6 transit routers.		contain IPv6 EHs (and possibly IPv6 options) at IPv6 transit routers.
	It is meant to improve the current situation of widespread dropping		It is meant to improve the current situation of widespread dropping
	of such IPv6 packets in those cases where the drops result from		of such IPv6 packets in those cases where the drops result from
	improper configuration defaults, or inappropriate advice in this		improper configuration defaults, or inappropriate advice in this
	area.		area.
			As discussed in Section Section 3.3 of this document, one of the
			underlying principles for the advice provided in this document is
			that IPv6 packets with specific EHs or options which 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 ased on the presence of IPv6 EHs or options might
			itself represent an attack vector to network infrastructure devices
			[RFC9098].
	8. Acknowledgements		8. Acknowledgements
	The authors would like to thank Ron Bonica for his work on earlier		The authors would like to thank Ron Bonica for his work on earlier
	versions of this document.		versions of this document.
	The authors of this document would like to thank (in alphabetical		The authors of this document would like to thank (in alphabetical
	order) Mikael Abrahamsson, Brian Carpenter, Darren Dukes, Lars		order) Mikael Abrahamsson, Brian Carpenter, Tim Chown, Roman Danyliw,
	Eggert, David Farmer, Mike Heard, Bob Hinden, Christian Huitema,		Darren Dukes, Lars Eggert, David Farmer, Mike Heard, Bob Hinden,
	Benjamin Kaduk, Erik Kline, Jen Linkova, Carlos Pignataro, Alvaro		Christian Huitema, Benjamin Kaduk, Erik Kline, Murray Kucherawy, Jen
	Retana, Maria Ines Robles, Donald Smith, Pascal Thubert, Ole Troan,		Linkova, Carlos Pignataro, Alvaro Retana, Maria Ines Robles,
	Gunter Van De Velde, and Eric Vyncke, for providing valuable comments		Zaheduzzaman Sarker, Donald Smith, Pascal Thubert, Ole Troan, Gunter
	on earlier versions of this document.		Van De Velde, Eric Vyncke, and Robert Wilton, for providing valuable
			comments on earlier versions of this document.
	This document borrows some text and analysis from [RFC7126], authored		This document borrows some text and analysis from [RFC7126], authored
	by Fernando Gont, Randall Atkinson, and Carlos Pignataro.		by Fernando Gont, Randall Atkinson, and Carlos Pignataro.
	The authors would like to thank Eric Vyncke for his guidance during		The authors would like to thank Warren Kumari and Eric Vyncke for
	the publication process of this document.		their guidance during the publication process of this document.
	Fernando would also like to thank Brian Carpenter and Ran Atkinson		Fernando would also like to thank Brian Carpenter and Ran Atkinson
	who, over the years, have answered many questions and provided		who, over the years, have answered many questions and provided
	valuable comments that have benefited his protocol-related work		valuable comments that have benefited his protocol-related work
	(including the present document).		(including the present document).
	9. References		9. References
	9.1. Normative References		9.1. Normative References
	skipping to change at page 35, line 14 ¶		skipping to change at page 37, line 23 ¶
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6		[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
	(IPv6) Specification", STD 86, RFC 8200,		(IPv6) Specification", STD 86, RFC 8200,
	DOI 10.17487/RFC8200, July 2017,		DOI 10.17487/RFC8200, July 2017,
	<https://www.rfc-editor.org/info/rfc8200>.		<https://www.rfc-editor.org/info/rfc8200>.
			[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.,		[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
	Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header		Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
	(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,		(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
	<https://www.rfc-editor.org/info/rfc8754>.		<https://www.rfc-editor.org/info/rfc8754>.
	[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,		[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O.,
	and F. Gont, "IP Fragmentation Considered Fragile",		and F. Gont, "IP Fragmentation Considered Fragile",
	BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,		BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
	<https://www.rfc-editor.org/info/rfc8900>.		<https://www.rfc-editor.org/info/rfc8900>.
	skipping to change at page 36, line 13 ¶		skipping to change at page 38, line 28 ¶
	00.txt, November 1995.		00.txt, November 1995.
	[FW-Benchmark]		[FW-Benchmark]
	Zack, E., "Firewall Security Assessment and Benchmarking		Zack, E., "Firewall Security Assessment and Benchmarking
	IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1,		IPv6 Firewall Load Tests", IPv6 Hackers Meeting #1,
	Berlin, Germany. June 30, 2013,		Berlin, Germany. June 30, 2013,
	<https://www.ipv6hackers.org/files/meetings/ipv6-hackers-		<https://www.ipv6hackers.org/files/meetings/ipv6-hackers-
	1/zack-ipv6hackers1-firewall-security-assessment-and-		1/zack-ipv6hackers1-firewall-security-assessment-and-
	benchmarking.pdf>.		benchmarking.pdf>.
			[Huston-2022]
			Huston, G. and J. Damas, "IPv6 Fragmentation and EH
			Behaviours", IEPG Meeting - March 2022 @ IETF 113, March
			2022,
			<https://iepg.org/2022-03-20-ietf113/huston-v6frag.pdf>.
	[I-D.irtf-pearg-numeric-ids-generation]		[I-D.irtf-pearg-numeric-ids-generation]
	Gont, F. and I. Arce, "On the Generation of Transient		Gont, F. and I. Arce, "On the Generation of Transient
	Numeric Identifiers", Work in Progress, Internet-Draft,		Numeric Identifiers", Work in Progress, Internet-Draft,
	draft-irtf-pearg-numeric-ids-generation-08, 31 January		draft-irtf-pearg-numeric-ids-generation-08, 31 January
	2022, <https://www.ietf.org/archive/id/draft-irtf-pearg-		2022, <https://www.ietf.org/archive/id/draft-irtf-pearg-
	numeric-ids-generation-08.txt>.		numeric-ids-generation-08.txt>.
			[I-D.vyncke-v6ops-james]
			Vyncke, É., Léas, R., and J. Iurman, "Just Another
			Measurement of Extension header Survivability (JAMES)",
			Work in Progress, Internet-Draft, draft-vyncke-v6ops-
			james-01, 19 March 2022, <https://www.ietf.org/archive/id/
			draft-vyncke-v6ops-james-01.txt>.
	[IANA-IPV6-PARAM]		[IANA-IPV6-PARAM]
	Internet Assigned Numbers Authority, "Internet Protocol		Internet Assigned Numbers Authority, "Internet Protocol
	Version 6 (IPv6) Parameters", December 2013,		Version 6 (IPv6) Parameters", December 2013,
	<https://www.iana.org/assignments/ipv6-parameters/		<https://www.iana.org/assignments/ipv6-parameters/
	ipv6-parameters.xhtml>.		ipv6-parameters.xhtml>.
	[IANA-PROTOCOLS]		[IANA-PROTOCOLS]
	Internet Assigned Numbers Authority, "Protocol Numbers",		Internet Assigned Numbers Authority, "Protocol Numbers",
	2014, <https://www.iana.org/assignments/protocol-numbers/		2014, <https://www.iana.org/assignments/protocol-numbers/
	protocol-numbers.xhtml>.		protocol-numbers.xhtml>.
	skipping to change at page 37, line 21 ¶		skipping to change at page 40, line 4 ¶
	Extension Headers in the Real World", RFC 7872,		Extension Headers in the Real World", RFC 7872,
	DOI 10.17487/RFC7872, June 2016,		DOI 10.17487/RFC7872, June 2016,
	<https://www.rfc-editor.org/info/rfc7872>.		<https://www.rfc-editor.org/info/rfc7872>.
	[RFC9098] Gont, F., Hilliard, N., Doering, G., Kumari, W., Huston,		[RFC9098] Gont, F., Hilliard, N., Doering, G., Kumari, W., Huston,
	G., and W. Liu, "Operational Implications of IPv6 Packets		G., and W. Liu, "Operational Implications of IPv6 Packets
	with Extension Headers", RFC 9098, DOI 10.17487/RFC9098,		with Extension Headers", RFC 9098, DOI 10.17487/RFC9098,
	September 2021, <https://www.rfc-editor.org/info/rfc9098>.		September 2021, <https://www.rfc-editor.org/info/rfc9098>.
	Authors' Addresses		Authors' Addresses
	Fernando Gont		Fernando Gont
	SI6 Networks		EdgeUno
	Segurola y Habana 4310, 7mo Piso		Segurola y Habana 4310, 7mo Piso
	Villa Devoto		Villa Devoto
	Ciudad Autonoma de Buenos Aires		Ciudad Autonoma de Buenos Aires
	Argentina		Argentina
	Email: fgont@si6networks.com		Email: fernando.gont@edgeuno.com
	URI: https://www.si6networks.com		URI: https://www.edgeuno.com
	Will (Shucheng) Liu		Will (Shucheng) Liu
	Huawei Technologies		Huawei Technologies
	Bantian, Longgang District		Bantian, Longgang District
	Shenzhen		Shenzhen
	518129		518129
	P.R. China		P.R. China
	Email: liushucheng@huawei.com		Email: liushucheng@huawei.com
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