draft-ietf-v6ops-ra-guard-implementation-07.txt		rfc7113.txt
	IPv6 Operations Working Group (v6ops) F. Gont		Internet Engineering Task Force (IETF) F. Gont
	Internet-Draft UK CPNI		Request for Comments: 7113 Huawei Technologies
	Updates: 6105 (if approved) November 14, 2012		Updates: 6105 February 2014
	Intended status: Informational		Category: Informational
	Expires: May 18, 2013		ISSN: 2070-1721
	Implementation Advice for IPv6 Router Advertisement Guard (RA-Guard)		Implementation Advice for IPv6 Router Advertisement Guard (RA-Guard)
	draft-ietf-v6ops-ra-guard-implementation-07
	Abstract		Abstract
	The IPv6 Router Advertisement Guard (RA-Guard) mechanism is commonly		The IPv6 Router Advertisement Guard (RA-Guard) mechanism is commonly
	employed to mitigate attack vectors based on forged ICMPv6 Router		employed to mitigate attack vectors based on forged ICMPv6 Router
	Advertisement messages. Many existing IPv6 deployments rely on RA-		Advertisement messages. Many existing IPv6 deployments rely on
	Guard as the first line of defense against the aforementioned attack		RA-Guard as the first line of defense against the aforementioned
	vectors. However, some implementations of RA-Guard have been found		attack vectors. However, some implementations of RA-Guard have been
	to be prone to circumvention by employing IPv6 Extension Headers.		found to be prone to circumvention by employing IPv6 Extension
	This document describes the evasion techniques that affect the		Headers. This document describes the evasion techniques that affect
	aforementioned implementations, and formally updates RFC 6105, such		the aforementioned implementations and formally updates RFC 6105,
	that the aforementioned RA-Guard evasion vectors are eliminated.		such that the aforementioned RA-Guard evasion vectors are eliminated.
	Status of this Memo
	This Internet-Draft is submitted in full conformance with the		Status of This Memo
	provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		This document is not an Internet Standards Track specification; it is
	Task Force (IETF). Note that other groups may also distribute		published for informational purposes.
	working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		This document is a product of the Internet Engineering Task Force
	and may be updated, replaced, or obsoleted by other documents at any		(IETF). It represents the consensus of the IETF community. It has
	time. It is inappropriate to use Internet-Drafts as reference		received public review and has been approved for publication by the
	material or to cite them other than as "work in progress."		Internet Engineering Steering Group (IESG). Not all documents
			approved by the IESG are a candidate for any level of Internet
			Standard; see Section 2 of RFC 5741.
	This Internet-Draft will expire on May 18, 2013.		Information about the current status of this document, any errata,
			and how to provide feedback on it may be obtained at
			http://www.rfc-editor.org/info/rfc7113.
	Copyright Notice		Copyright Notice
	Copyright (c) 2012 IETF Trust and the persons identified as the		Copyright (c) 2014 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Evasion techniques for some Router Advertisement Guard (RA		2. Evasion Techniques for Some RA-Guard Implementations . . . . . 3
	Guard) implementations . . . . . . . . . . . . . . . . . . . . 4		2.1. Attack Vector Based on IPv6 Extension Headers . . . . . . 3
	2.1. Attack Vector based on IPv6 Extension Headers . . . . . . 4		2.2. Attack Vector Based on IPv6 Fragmentation . . . . . . . . 4
	2.2. Attack vector based on IPv6 fragmentation . . . . . . . . 4		3. RA-Guard Implementation Advice . . . . . . . . . . . . . . . . 6
	3. RA-Guard implementation advice . . . . . . . . . . . . . . . . 8		4. Other Implications . . . . . . . . . . . . . . . . . . . . . . 9
	4. Other Implications . . . . . . . . . . . . . . . . . . . . . . 11		5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12		6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 13		7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
	7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14		7.1. Normative References . . . . . . . . . . . . . . . . . . . 10
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15		7.2. Informative References . . . . . . . . . . . . . . . . . . 11
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 15		Appendix A. Assessment Tools . . . . . . . . . . . . . . . . . . 12
	8.2. Informative References . . . . . . . . . . . . . . . . . . 15
	Appendix A. Assessment tools . . . . . . . . . . . . . . . . . . 17
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18
	1. Introduction		1. Introduction
	IPv6 Router Advertisement Guard (RA-Guard) is a mitigation technique		IPv6 Router Advertisement Guard (RA-Guard) is a mitigation technique
	for attack vectors based on ICMPv6 Router Advertisement messages.		for attack vectors based on ICMPv6 Router Advertisement [RFC4861]
	[RFC6104] describes the problem statement of "Rogue IPv6 Router		messages. [RFC6104] describes the problem statement of "Rogue IPv6
	Advertisements", and [RFC6105] specifies the "IPv6 Router		Router Advertisements", and [RFC6105] specifies the "IPv6 Router
	Advertisement Guard" functionality.		Advertisement Guard" functionality.
	The concept behind RA-Guard is that a layer-2 device filters ICMPv6		The concept behind RA-Guard is that a Layer-2 (L2) device filters
	Router Advertisement messages, according to a number of different		ICMPv6 Router Advertisement messages, according to a number of
	criteria. The most basic filtering criterion is that Router		different criteria. The most basic filtering criterion is that
	Advertisement messages are discarded by the layer-2 device unless		Router Advertisement messages are discarded by the L2 device unless
	they are received on a specified port of the layer-2 device.		they are received on a specified port of the L2 device. Clearly, the
	Clearly, the effectiveness of the RA Guard mitigation relies on the		effectiveness of RA-Guard relies on the ability of the L2 device to
	ability of the layer-2 device to identify ICMPv6 Router Advertisement		identify ICMPv6 Router Advertisement messages.
	messages.
	Some popular RA-Guard implementations have been found to be easy to		Some popular RA-Guard implementations have been found to be easy to
	circumvent by employing IPv6 extension headers [CPNI-IPv6]. This		circumvent by employing IPv6 Extension Headers [CPNI-IPv6]. This
	document describes such evasion techniques, and provides advice to		document describes such evasion techniques and provides advice to
	RA-Guard implementers such that the aforementioned evasion vectors		RA-Guard implementers such that the aforementioned evasion vectors
	can be eliminated.		can be eliminated.
	It should be noted that the aforementioned techniques could also be		It should be noted that the previously mentioned techniques could
	exploited to evade network monitoring tools such as NDPMon [NDPMon],		also be exploited to evade network monitoring tools such as NDPMon
	ramond [ramond], and rafixd [rafixd], and could probably be exploited		[NDPMon], ramond [ramond], and rafixd [rafixd], and could probably be
	to perform stealth DHCPv6 attacks.		exploited to perform stealth DHCPv6 [RFC3315] attacks.
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in RFC 2119 [RFC2119].
	2. Evasion techniques for some Router Advertisement Guard (RA Guard)		2. Evasion Techniques for Some RA-Guard Implementations
	implementations
	The following subsections describe two different vectors that have		The following subsections describe two different vectors that have
	been found to be effective for the evasion of popular implementations		been found to be effective for the evasion of popular implementations
	of the RA-Guard protection. Section 2.1 describes an attack vector		of RA-Guard. Section 2.1 describes an attack vector based on the use
	based on the use of IPv6 Extension Headers with the ICMPv6 Router		of IPv6 Extension Headers with ICMPv6 Router Advertisement messages,
	Advertisement messages, which may be used to circumvent the RA-Guard		which may be used to circumvent the RA-Guard protection of those
	protection of those implementations that fail to process an entire		implementations that fail to process an entire IPv6 header chain when
	IPv6 header chain when trying to identify the ICMPv6 Router		trying to identify the ICMPv6 Router Advertisement messages.
	Advertisement messages. Section 2.2 describes an attack method based		Section 2.2 describes an attack method based on the use of IPv6
	on the use of IPv6 fragmentation, possibly in conjunction with the		fragmentation, possibly in conjunction with the use of IPv6 Extension
	use of IPv6 Extension Headers. This later vector has been found to		Headers. This later vector has been found to be effective against
	be effective with all existing implementations of the RA-Guard		all existing implementations of RA-Guard.
	mechanism.
	2.1. Attack Vector based on IPv6 Extension Headers		2.1. Attack Vector Based on IPv6 Extension Headers
	While there is currently no legitimate use for IPv6 Extension Headers		While there is currently no legitimate use for IPv6 Extension Headers
	in ICMPv6 Router Advertisement messages, Neighbor Discovery		in ICMPv6 Router Advertisement messages, Neighbor Discovery [RFC4861]
	implementations allow the use of Extension Headers with these		implementations allow the use of Extension Headers with these
	messages, by simply ignoring the received options. Some RA-Guard		messages, by simply ignoring the received options. Some RA-Guard
	implementations try to identify ICMPv6 Router Advertisement messages		implementations try to identify ICMPv6 Router Advertisement messages
	by simply looking at the "Next Header" field of the fixed IPv6		by simply looking at the "Next Header" field of the fixed IPv6
	header, rather than following the entire header chain. As a result,		header, rather than following the entire header chain. As a result,
	such implementations fail to identify any ICMPv6 Router Advertisement		such implementations fail to identify any ICMPv6 Router Advertisement
	messages that include any Extension Headers (for example, a Hop by		messages that include any Extension Headers (for example, a Hop-by-
	Hop Options header, a Destination Options Header, etc.), and can be		Hop Options header, a Destination Options header, etc.), and can be
	easily circumvented.		easily circumvented.
	The following figure illustrates the structure of ICMPv6 Router		The following figure illustrates the structure of ICMPv6 Router
	Advertisement messages that implement this evasion technique:		Advertisement messages that implement this evasion technique:
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|NH=60| |NH=58| | |		|NH=60| |NH=58| | |
	+-+-+-+ +-+-+-+ + +		+-+-+-+ +-+-+-+ + +
	| IPv6 header | Dst Opt Hdr | ICMPv6 Router Advertisement |		| IPv6 Header | Dst Opt Hdr | ICMPv6 Router Advertisement |
	+ + + +		+ + + +
	| | | |		| | | |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	2.2. Attack vector based on IPv6 fragmentation		2.2. Attack Vector Based on IPv6 Fragmentation
	This section presents a different attack vector, which has been found		This section presents a different attack vector, which has been found
	to be effective against all implementations of RA-Guard. The basic		to be effective against all implementations of RA-Guard. The basic
	idea behind this attack vector is that if the forged ICMPv6 Router		idea behind this attack vector is that if the forged ICMPv6 Router
	Advertisement is fragmented into at least two fragments, the layer-2		Advertisement is fragmented into at least two fragments, the L2
	device implementing "RA-Guard" would be unable to identify the attack		device implementing RA-Guard would be unable to identify the attack
	packet, and would thus fail to block it.		packet and would thus fail to block it.
	A first variant of this attack vector would be an original ICMPv6		A first variant of this attack vector would be an original ICMPv6
	Router Advertisement message preceded with a Destination Options		Router Advertisement message preceded with a Destination Options
	Header, that results in two fragments. The following figure		header, which results in two fragments. The following figure
	illustrates the "original" attack packet, prior to fragmentation, and		illustrates the "original" attack packet, prior to fragmentation, and
	the two resulting fragments which are actually sent as part of the		the two resulting fragments that are actually sent as part of the
	attack.		attack.
	Original packet:		Original Packet:
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|NH=60| |NH=58| | |		|NH=60| |NH=58| | |
	+-+-+-+ +-+-+-+ + +		+-+-+-+ +-+-+-+ + +
	| IPv6 header | Dst Opt Hdr | ICMPv6 RA |		| IPv6 Header | Dst Opt Hdr | ICMPv6 RA |
	+ + + +		+ + + +
	| | | |		| | | |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	First fragment:		First Fragment:
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|NH=44| |NH=60| |NH=58| |		|NH=44| |NH=60| |NH=58| |
	+-+-+-+ +-+-+-+ +-+-+-+ +		+-+-+-+ +-+-+-+ +-+-+-+ +
	| IPv6 Header | Frag Hdr | Dst Opt Hdr |		| IPv6 Header | Frag Hdr | Dst Opt Hdr |
	+ + + +		+ + + +
	| | | |		| | | |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Second fragment:		Second Fragment:
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|NH=44| |NH=60| | | |		|NH=44| |NH=60| | | |
	+-+-+-+ +-+-+-+ + + +		+-+-+-+ +-+-+-+ + + +
	| IPv6 header | Frag Hdr | Dst Opt Hdr | ICMPv6 RA |		| IPv6 Header | Frag Hdr | Dst Opt Hdr | ICMPv6 RA |
	+ + + + +		+ + + + +
	| | | | |		| | | | |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	It should be noted that the "Hdr Ext Len" field of the Destination		It should be noted that the "Hdr Ext Len" field of the Destination
	Options Header is present in the first fragment (rather than the		Options header is present in the First Fragment (rather than the
	second). Therefore, it is impossible for a device processing only		second). Therefore, it is impossible for a device processing only
	the second fragment to locate the ICMPv6 header contained in that		the second fragment to locate the ICMPv6 header contained in that
	fragment, since it is unknown how many bytes should be "skipped" to		fragment, since it is unknown how many bytes should be "skipped" to
	get to the next header following the Destination Options Header.		get to the next header following the Destination Options header.
	Thus, by leveraging the use of the Fragment Header together with the		Thus, by leveraging the use of the Fragment Header together with the
	use of the Destination Options header, the attacker is able to		use of the Destination Options header, the attacker is able to
	conceal the type and contents of the ICMPv6 message he is sending (an		conceal the type and contents of the ICMPv6 message he is sending (an
	ICMPv6 Router Advertisement in this example). Unless the layer-2		ICMPv6 Router Advertisement in this example). Unless the L2 device
	device were to implement IPv6 fragment reassembly, it would be		were to implement IPv6 fragment reassembly, it would be impossible
	impossible for the device to identify the ICMPv6 type of the message.		for the device to identify the ICMPv6 type of the message.
	A layer-2 device could, however, at least detect that that an		An L2 device could, however, at least detect that an ICMPv6
	ICMPv6 message (or some type) is being sent, since the "Next		message (of some type) is being sent, since the "Next Header"
	Header" field of the Destination Options header contained in the		field of the Destination Options header contained in the First
	first fragment is set to "58" (ICMPv6).		Fragment is set to "58" (ICMPv6).
	This idea can be taken further, such that it is also impossible for		This idea can be taken further, such that it is also impossible for
	the layer-2 device to detect that the attacker is sending an ICMPv6		the L2 device to detect that the attacker is sending an ICMPv6
	message in the first place. This can be achieved with an original		message in the first place. This can be achieved with an original
	ICMPv6 Router Advertisement message preceded with two Destination		ICMPv6 Router Advertisement message preceded with two Destination
	Options Headers, that results in two fragments. The following figure		Options headers that results in two fragments. The following figure
	illustrates the "original" attack packet, prior to fragmentation, and		illustrates the "original" attack packet, prior to fragmentation, and
	the two resulting packets which are actually sent as part of the		the two resulting packets that are actually sent as part of the
	attack.		attack.
	Original packet:		Original Packet:
	+-+-+-+-+-+-+-+-+-+-+-+-//+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-//+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|NH=60| |NH=60| |NH=58| | |		|NH=60| |NH=60| |NH=58| | |
	+-+-+-+ +-+-+-+ +-+-+-+ + +		+-+-+-+ +-+-+-+ +-+-+-+ + +
	| IPv6 header | Dst Opt Hdr | Dst Opt Hdr | ICMPv6 RA |		| IPv6 header | Dst Opt Hdr | Dst Opt Hdr | ICMPv6 RA |
	+ + + + +		+ + + + +
	| | | | |		| | | | |
	+-+-+-+-+-+-+-+-+-+-+-+-//+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-//+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	First fragment:		First Fragment:
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|NH=44| |NH=60| |NH=60| |		|NH=44| |NH=60| |NH=60| |
	+-+-+-+ +-+-+-+ +-+-+-+ +		+-+-+-+ +-+-+-+ +-+-+-+ +
	| IPv6 header | Frag Hdr | Dst Opt Hdr |		| IPv6 header | Frag Hdr | Dst Opt Hdr |
	+ + + +		+ + + +
	| | | |		| | | |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			Second Fragment:
	Second fragment:
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|NH=44| |NH=60| | |NH=58| | |		|NH=44| |NH=60| | |NH=58| | |
	+-+-+-+ +-+-+-+ + +-+-+-+ + +		+-+-+-+ +-+-+-+ + +-+-+-+ + +
	| IPv6 header | Frag Hdr | Dst O Hdr | Dst Opt Hdr | ICMPv6 RA |		| IPv6 header | Frag Hdr | Dst O Hdr | Dst Opt Hdr | ICMPv6 RA |
	+ + + + + +		+ + + + + +
	| | | | | |		| | | | | |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	In this variant, the "Next Header" field of the Destination Options		In this variant, the "Next Header" field of the Destination Options
	header contained in the first fragment is set "60" (Destination		header contained in the First Fragment is set to "60" (Destination
	Options header), and thus it is impossible for a device processing		Options header); thus, it is impossible for a device processing only
	only the first fragment to detect that an ICMPv6 message is being		the First Fragment to detect that an ICMPv6 message is being sent in
	sent in the first place.		the first place.
	The second fragment presents the same challenges as the second		The second fragment presents the same challenges as the second
	fragment of the previous variant. That is, it would be impossible		fragment of the previous variant. That is, it would be impossible
	for a device processing only the second fragment to locate the second		for a device processing only the second fragment to locate the second
	Destination Options header (and hence the ICMPv6 header), since the		Destination Options header (and hence the ICMPv6 header), since the
	"Hdr Ext Len" field of the first Destination Options header is		"Hdr Ext Len" field of the first Destination Options header is
	present in the first fragment (rather than the second).		present in the First Fragment (rather than the second).
	3. RA-Guard implementation advice		3. RA-Guard Implementation Advice
	The following filtering rules must be implemented as part of an "RA-		The following filtering rules must be implemented as part of an
	Guard" implementation on ports that face interfaces that are not		RA-Guard implementation on ports that face interfaces that are not
	allowed to send ICMPv6 Router Advertisement messages, such that the		allowed to send ICMPv6 Router Advertisement messages, such that the
	vulnerabilities discussed in this document are eliminated:		vulnerabilities discussed in this document are eliminated:
	1. If the IPv6 Source Address of the packet is not a link-local		1. If the IPv6 Source Address of the packet is not a link-local
	address (fe80::/10), RA-Guard must pass the packet.		address (fe80::/10), RA-Guard must pass the packet.
	RATIONALE: This prevents "RA-Guard" from dedicating compute		RATIONALE: This prevents RA-Guard from dedicating processing
	cycles to filtering packets that originate off-net and, if		cycles to filtering packets that originate off-net and that,
	they are RA's, would not be accepted by the host. Section		if they are RA's, would not be accepted by the host. Section
	6.1.2 of [RFC4861] requires nodes to discard Router		6.1.2 of [RFC4861] requires nodes to discard Router
	Advertisement messages if their IPv6 Source Address is not a		Advertisement messages if their IPv6 Source Address is not a
	link-local address.		link-local address.
	2. If the Hop Limit is not 255, RA-Guard must pass the packet.		2. If the Hop Limit is not 255, RA-Guard must pass the packet.
	RATIONALE: This prevents "RA-Guard" from dedicating compute		RATIONALE: This prevents RA-Guard from dedicating processing
	cycles to filtering packets that originate off-net and, if		cycles to filtering packets that originate off-net and that,
	they are RA's, would not be accepted by the host. Section		if they are RA's, would not be accepted by the destination
	6.1.2 of [RFC4861] requires nodes to discard Router		host. Section 6.1.2 of [RFC4861] requires nodes to discard
	Advertisement messages if their Hop Limit is not 255.		Router Advertisement messages if their Hop Limit is not 255.
	3. RA-Guard must parse the IPv6 entire header chain present in the		3. RA-Guard must parse the entire IPv6 header chain present in the
	packet, to identify whether the packet is a Router Advertisement		packet, to identify whether the packet is a Router Advertisement
	message.		message.
	RATIONALE: [RFC6564] specifies a uniform format for IPv6		NOTE: RA-Guard implementations must not enforce a limit on the
	Extension Header, thus meaning that an IPv6 node can parse an
	IPv6 header chain even if it contains Extension Headers that
	are not currently supported by that node. Additionally,
	[I-D.ietf-6man-oversized-header-chain] requires that if a
	packet is fragmented, the first fragment contains the entire
	IPv6 header chain.
	RA-Guard implementations must not enforce a limit on the
	number of bytes they can inspect (starting from the beginning		number of bytes they can inspect (starting from the beginning
	of the IPv6 packet), since this could introduce false-		of the IPv6 packet), since this could introduce false
	positives: legitimate packets could be dropped simply because		positives: legitimate packets could be dropped simply because
	the RA-Guard device does not parse the entire IPv6 header		the RA-Guard device does not parse the entire IPv6 header
	chain present in the packet. An implementation that has such		chain present in the packet. An implementation that has such
	an implementation-specific limit must not claim compliance		an implementation-specific limit must not claim compliance
	with this specification, and must pass the packet when such		with this specification, and must pass the packet when such
	implementation-specific limit is reached.		implementation-specific limit is reached.
	4. When parsing the IPv6 header chain, if the packet is a first-		4. When parsing the IPv6 header chain, if the packet is a First
	fragment (i.e., a packet containing a Fragment Header with the		Fragment (i.e., a packet containing a Fragment Header with the
	Fragment Offset set to 0) and it fails to contain the entire IPv6		Fragment Offset set to 0) and it fails to contain the entire IPv6
	header chain (i.e., all the headers starting from the IPv6 header		header chain (i.e., all the headers starting from the IPv6 header
	up to, and including, the upper-layer header), RA-Guard must drop		up to, and including, the upper-layer header), RA-Guard must drop
	the packet, and should log the packet drop event in an		the packet and should log the packet drop event in an
	implementation-specific manner as a security fault.		implementation-specific manner as a security fault.
	RATIONALE: [I-D.ietf-6man-oversized-header-chain] specifies		RATIONALE: [RFC7112] specifies that the First Fragment (i.e.,
	that the first-fragment (i.e., the fragment with the Fragment		the fragment with the Fragment Offset set to 0) must contain
	Offset set to 0) MUST contain the entire IPv6 header chain,		the entire IPv6 header chain, and allows intermediate systems
	and allows intermmediate systems such as routers to drop those		such as routers to drop those packets that fail to comply with
	packets that fail to comply with this requirement.		this requirement.
	NOTE: This rule should only be applied to IPv6 fragments with		NOTE: This rule should only be applied to IPv6 fragments with
	a Fragment Offset of 0 (non-first fragments can be safely		a Fragment Offset of 0 (non-First Fragments can be safely
	passed, since they will never reassemble into a complete		passed, since they will never reassemble into a complete
	datagram if they are part of a Router Advertisement received		datagram if they are part of a Router Advertisement received
	on a port where such packets are not allowed).		on a port where such packets are not allowed).
	5. When parsing the IPv6 header chain, if the packet is identified		5. When parsing the IPv6 header chain, if the packet is identified
	to be an ICMPv6 Router Advertisement message, RA-Guard must drop		to be an ICMPv6 Router Advertisement message or the packet
	the packet, and should log the packet drop event in an		contains an unrecognized Next Header value [IANA-IP-PROTO],
	implementation-specific manner as a security fault.		RA-Guard must drop the packet, and should log the packet drop
			event in an implementation-specific manner as a security fault.
			RA-Guard must provide a configuration knob that controls whether
			packets with unrecognized Next Header values are dropped; this
			configuration knob must default to "drop".
	RATIONALE: By definition, Router Advertisement messages MUST		RATIONALE: By definition, Router Advertisement messages are
	originate on-link, MUST have a link-local IPv6 Source Address,		required to originate on-link, have a link-local IPv6 Source
	and MUST have a Hop Limit value of 255. [RFC4861].		Address, and have a Hop Limit value of 255 [RFC4861].
			[RFC7045] requires that nodes be configurable with respect to
			whether packets with unrecognized headers are forwarded, and
			allows the default behavior to be that such packets be
			dropped.
	6. In all other cases, RA-Guard must pass the packet as usual.		6. In all other cases, RA-Guard must pass the packet as usual.
	NOTE: For the purpose of enforcing the RA-Guard filtering policy,		NOTE: For the purpose of enforcing the RA-Guard filtering policy,
	an ESP header [RFC4303] should be considered to be an "upper-layer		an Encapsulating Security Payload (ESP) header [RFC4303] should be
	protocol" (that is, it should be considered the last header in the		considered to be an "upper-layer protocol" (that is, it should be
	IPv6 header chain). This means that packets employing ESP would		considered the last header in the IPv6 header chain). This means
	be passed by the RA-Guard device to the intended destination. If		that packets employing ESP would be passed by the RA-Guard device
	the destination host does not have a security association with the		to the intended destination. If the destination host does not
	sender of the aforementioned IPv6 packet, the packet would be		have a security association with the sender of the aforementioned
	dropped. Otherwise, if the packet is considered valid by the		IPv6 packet, the packet would be dropped. Otherwise, if the
	IPsec implementation at the receiving host and encapsulates a		packet is considered valid by the IPsec implementation at the
	Router Advertisement message, it is up to the receiving host what		receiving host and encapsulates a Router Advertisement message, it
	to do with such packet.		is up to the receiving host what to do with such a packet.
	If a packet is dropped due to this filtering policy, then the packet		If a packet is dropped due to this filtering policy, then the packet
	drop event should be logged in an implementation-specific manner as a		drop event should be logged in an implementation-specific manner as a
	security fault. The logging mechanism should include a drop counter		security fault. The logging mechanism should include a drop counter
	dedicated to RA-Guard packet drops.		dedicated to RA-Guard packet drops.
	In order to protect current end-node IPv6 implementations, Rule #4		In order to protect current end-node IPv6 implementations, Rule #4
	has been defined as a default rule to drop packets that cannot be		has been defined as a default rule to drop packets that cannot be
	positively identified as not being Router Advertisement (RA) messages		positively identified as not being Router Advertisement (RA) messages
	(because the packet is a fragment that fails to include the entire		(because the packet is a fragment that fails to include the entire
	IPv6 header chain). This means that, at least in theory, RA-Guard		IPv6 header chain). This means that, at least in theory, RA-Guard
	could result in false-positive blocking of some legitimate non-RA		could result in false-positive blocking of some legitimate non-RA
	packets that could not be positively identified as being non-RA. In		packets that could not be positively identified as being non-RA. In
	order to reduce the likelihood of false positives, Rule #1 and Rule		order to reduce the likelihood of false positives, Rule #1 and Rule
	#2 require that packets that would not pass the required validation		#2 require that packets that would not pass the required validation
	checks for RA messages (Section 6.1.2 of [RFC4861]) be passed without		checks for RA messages (Section 6.1.2 of [RFC4861]) be passed without
	further inspection. In any case, as noted in		further inspection. In any case, as noted in [RFC7112], IPv6 packets
	[I-D.ietf-6man-oversized-header-chain], IPv6 packets that fail to		that fail to include the entire IPv6 header chain are virtually
	include the entire IPv6 header chain are virtually impossible to		impossible to police with state-less filters and firewalls and,
	police with state-less filters and firewalls, and hence are unlikely		hence, are unlikely to survive in real networks. [RFC7112] requires
	to survive in real networks. [I-D.ietf-6man-oversized-header-chain]		that hosts employing fragmentation include the entire IPv6 header
	requires that hosts employing fragmentation include the entire IPv6		chain in the First Fragment (the fragment with the Fragment Offset
	header chain in the first fragment (the fragment with the Fragment		set to 0), thus eliminating the aforementioned false positives.
	Offset set to 0), thus eliminating the aforementioned false
	positives.
	This filtering policy assumes that host implementations require that		This filtering policy assumes that host implementations require that
	the IPv6 Source Address of ICMPv6 Router Advertisement messages be a		the IPv6 Source Address of ICMPv6 Router Advertisement messages be a
	link-local address, and that they discard the packet if this check		link-local address and that they discard the packet if this check
	fails, as required by the current IETF specifications [RFC4861].		fails, as required by the current IETF specifications [RFC4861].
	Additionally, it assumes that hosts require the Hop Limit of Neighbor		Additionally, it assumes that hosts require the Hop Limit of Neighbor
	Discovery messages to be 255, and discard those packets otherwise.		Discovery messages to be 255, and that they discard those packets
			otherwise.
	The aforementioned filtering rules implicitly handle the case of		The aforementioned filtering rules implicitly handle the case of
	fragmented packets: if the RA-Guard device fails to identify the		fragmented packets: if the RA-Guard device fails to identify the
	upper-layer protocol as a result of the use of fragmentation, the		upper-layer protocol as a result of the use of fragmentation, the
	corresponding packets would be dropped.		corresponding packets would be dropped.
	Finally, we note that IPv6 implementations that allow overlapping		Finally, we note that IPv6 implementations that allow overlapping
	fragments (i.e. that do not comply with [RFC5722]) might still be		fragments (i.e., that do not comply with [RFC5722]) might still be
	subject of RA-based attacks. However, a recent assessment of IPv6		subject of RA-based attacks. However, a recent assessment of IPv6
	implementations [SI6-FRAG] with respect to their fragment reassembly		implementations [SI6-FRAG] with respect to their fragment reassembly
	policy seems to indicate that most current implementations comply		policy seems to indicate that most current implementations comply
	with [RFC5722].		with [RFC5722].
	4. Other Implications		4. Other Implications
	A similar concept to that of "RA-Guard" has been implemented for		A similar concept to that of RA-Guard has been implemented for
	protecting against forged DHCPv6 messages. Such protection can be		protecting against forged DHCPv6 messages. Such protection can be
	circumvented with the same techniques discussed in this document, and		circumvented with the same techniques discussed in this document, and
	the counter-measures for such evasion attack are analogous to those		the countermeasures for such evasion attack are analogous to those
	described in Section 3 of this document.		described in Section 3 of this document.
	[DHCPv6-Shield] specifies a mechanism to protect against rogue		[DHCPv6-Shield] specifies a mechanism to protect against rogue
	DHCPv6 servers, while taking into consideration the evasion		DHCPv6 servers, while taking into consideration the evasion
	techniques discussed in this document.		techniques discussed in this document.
	5. IANA Considerations		5. Security Considerations
	This document has no actions for IANA.
	6. Security Considerations
	This document describes a number of techniques that have been found		This document describes a number of techniques that have been found
	to be effective to circumvent popular RA-Guard implementations, and		to be effective to circumvent popular RA-Guard implementations and
	provides advice to RA-Guard implementations such that those evasion		provides advice to RA-Guard implementers such that those evasion
	vulnerabilities are eliminated.		vulnerabilities are eliminated.
	As noted in Section 3, IPv6 implementations that allow overlapping		As noted in Section 3, IPv6 implementations that allow overlapping
	fragments (i.e. that do not comply with [RFC5722]) might still be		fragments (i.e., that do not comply with [RFC5722]) might still be
	subject of RA-based attacks. However, most current		subject of RA-based attacks. However, most current
	implementations seem to comply with [RFC5722].		implementations seem to comply with [RFC5722].
	We note that if an attacker sends a fragmented Router Advertisement		We note that if an attacker sends a fragmented ICMPv6 Router
	message on a port not allowed to send such packets, the first-		Advertisement message on a port not allowed to send such packets, the
	fragment would be dropped, and the rest of the fragments would be		First Fragment would be dropped, and the rest of the fragments would
	passed. This means that the victim node would tie memory buffers for		be passed. This means that the victim node would tie memory buffers
	the aforementioned fragments, which would never reassemble into a		for the aforementioned fragments, which would never reassemble into a
	complete datagram. If a large number of such packets were sent by an		complete datagram. If a large number of such packets were sent by an
	attacker, and the victim node failed to implement proper resource		attacker, and the victim node failed to implement proper resource
	management for the fragment reassembly buffer, this could lead to a		management for the IPv6 fragment reassembly buffer, this could lead
	Denial of Service (DoS). However, this does not really introduce a		to a Denial of Service (DoS). However, this does not really
	new attack vector, since an attacker could always perform the same		introduce a new attack vector, since an attacker could always perform
	attack by sending forged fragmented datagram in which at least one of		the same attack by sending forged fragmented datagrams in which at
	the fragments is missing. [CPNI-IPv6] discusses some resource		least one of the fragments is missing. [CPNI-IPv6] discusses some
	management strategies that could be implemented for the fragment		resource management strategies that could be implemented for the IPv6
	reassembly buffer.		fragment reassembly buffer.
	We note that most effective and efficient mitigation for these		We note that the most effective and efficient mitigation for these
	attacks would be to prohibit the use of IPv6 fragmentation with		attacks would rely on the prohibiting the use of IPv6 fragmentation
	Router Advertisement messages (as proposed by		with Router Advertisement messages (as specified by [RFC6980]), such
	[I-D.ietf-6man-nd-extension-headers]), such that the RA-Guard		that the RA-Guard functionality is easier to implement. However,
	functionality is easier to implement. However, since such mitigation		since such mitigation would require an update to existing
	would require an update to existing implementations, it cannot be		implementations, it cannot be relied upon in the short or near term.
	relied upon in the short or near term.
	Finally, we note that RA-Guard only mitigates attack vectors based on		Finally, we note that RA-Guard only mitigates attack vectors based on
	ICMPv6 Router advertisement messages. Protection against similar		ICMPv6 Router advertisement messages. Protection against similar
	attacks based on other messages (such as DCHPv6) is considered out of		attacks based on other messages (such as DCHPv6) is considered out of
	the scope of this document, and left for other documents(e.g.		the scope of this document and is left for other documents (e.g.,
	[DHCPv6-Shield]).		[DHCPv6-Shield]).
	7. Acknowledgements		6. Acknowledgements
	The author would like to thank Ran Atkinson, who provided very		The author would like to thank Ran Atkinson, who provided very
	detailed comments and suggested text that was incorporated into this		detailed comments and suggested text that was incorporated into this
	document.		document.
	The author would like to thank Ran Atkinson, Karl Auer, Robert		The author would like to thank Ran Atkinson, Karl Auer, Robert
	Downie, Washam Fan, David Farmer, Marc Heuse, Nick Hilliard, Ray		Downie, Washam Fan, David Farmer, Mike Heard, Marc Heuse, Nick
	Hunter, Joel Jaeggli, Simon Perreault, Arturo Servin, Gunter van de		Hilliard, Ray Hunter, Joel Jaeggli, Simon Perreault, Arturo Servin,
	Velde, James Woodyatt, and Bjoern A. Zeeb, for providing valuable		Gunter van de Velde, James Woodyatt, and Bjoern A. Zeeb, for
	comments on earlier versions of this document.		providing valuable comments on earlier versions of this document.
	The author would like to thank Arturo Servin, who presented this		The author would like to thank Arturo Servin, who presented this
	document at IETF 81.		document at IETF 81.
	This document resulted from the project "Security Assessment of the		This document resulted from the project "Security Assessment of the
	Internet Protocol version 6 (IPv6)" [CPNI-IPv6], carried out by		Internet Protocol version 6 (IPv6)" [CPNI-IPv6], carried out by
	Fernando Gont on behalf of the UK Centre for the Protection of		Fernando Gont on behalf of the UK Centre for the Protection of
	National Infrastructure (CPNI). The author would like to thank the		National Infrastructure (CPNI).
	UK CPNI, for their continued support.
	8. References		7. References
	8.1. Normative References		7.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins,
	Requirement Levels", BCP 14, RFC 2119, March 1997.		C., and M. Carney, "Dynamic Host Configuration
			Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003.
	[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",		[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
	RFC 4303, December 2005.		RFC 4303, December 2005.
	[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,		[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H.
	"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,		Soliman, "Neighbor Discovery for IP version 6
	September 2007.		(IPv6)", RFC 4861, September 2007.
	[RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments",		[RFC5722] Krishnan, S., "Handling of Overlapping IPv6
	RFC 5722, December 2009.		Fragments", RFC 5722, December 2009.
	[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.		[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C.,
	Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,		and J. Mohacsi, "IPv6 Router Advertisement Guard",
	February 2011.		RFC 6105, February 2011.
	[RFC6564] Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and		[RFC6980] Gont, F., "Security Implications of IPv6
	M. Bhatia, "A Uniform Format for IPv6 Extension Headers",		Fragmentation with IPv6 Neighbor Discovery",
	RFC 6564, April 2012.		RFC 6980, August 2013.
	[I-D.ietf-6man-oversized-header-chain]		[RFC7045] Carpenter, B. and S. Jiang, "Transmission and
	Gont, F. and V. Manral, "Security and Interoperability		Processing of IPv6 Extension Headers", RFC 7045,
	Implications of Oversized IPv6 Header Chains",		December 2013.
	draft-ietf-6man-oversized-header-chain-02 (work in
	progress), November 2012.
	[I-D.ietf-6man-nd-extension-headers]		[RFC7112] Gont, F., Manral, V., and R. Bonica, "Implications
	Gont, F., "Security Implications of IPv6 Fragmentation		of Oversized IPv6 Header Chains", RFC 7112,
	with IPv6 Neighbor Discovery",		January 2014.
	draft-ietf-6man-nd-extension-headers-01 (work in
	progress), November 2012.
	8.2. Informative References		7.2. Informative References
	[RFC6104] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement		[CPNI-IPv6] Gont, F., "Security Assessment of the Internet
	Problem Statement", RFC 6104, February 2011.		Protocol version 6 (IPv6)", UK Centre for the
			Protection of National Infrastructure, (available on
			request).
	[DHCPv6-Shield]		[DHCPv6-Shield] Gont, F., Liu, W., and G. Van de Velde, "DHCPv6-
	Gont, F., "DHCPv6-Shield: Protecting Against Rogue DHCPv6		Shield: Protecting Against Rogue DHCPv6 Servers",
	Servers", IETF Internet Draft,		Work in Progress, October 2013.
	draft-gont-opsec-dhcpv6-shield, work in progress,
	May 2012.
	[CPNI-IPv6]		[IANA-IP-PROTO] IANA, "Assigned Internet Protocol Numbers",
	Gont, F., "Security Assessment of the Internet Protocol		<http://www.iana.org/assignments/protocol-numbers/>.
	version 6 (IPv6)", UK Centre for the Protection of
	National Infrastructure, (available on request).
	[NDPMon] "NDPMon - IPv6 Neighbor Discovery Protocol Monitor",		[NDPMon] "NDPMon - IPv6 Neighbor Discovery Protocol Monitor",
	<http://ndpmon.sourceforge.net/>.		<http://ndpmon.sourceforge.net/>.
	[rafixd] "rafixd", <http://www.kame.net/dev/cvsweb2.cgi/kame/kame/		[RFC6104] Chown, T. and S. Venaas, "Rogue IPv6 Router
	kame/rafixd/>.		Advertisement Problem Statement", RFC 6104,
			February 2011.
	[ramond] "ramond", <http://ramond.sourceforge.net/>.		[SI6-FRAG] SI6 Networks, "IPv6 NIDS evasion and improvements in
			IPv6 fragmentation/reassembly", 2012,
			<http://blog.si6networks.com/2012/02/
			ipv6-nids-evasion-and-improvements-in.html>.
	[SI6-FRAG]		[SI6-IPv6] "SI6 Networks' IPv6 toolkit",
	SI6 Networks, "IPv6 NIDS evasion and improvements in IPv6		<http://www.si6networks.com/tools/ipv6toolkit>.
	fragmentation/reassembly", 2012, <http://
	blog.si6networks.com/2012/02/
	ipv6-nids-evasion-and-improvements-in.html>.
	[SI6-IPv6]		[THC-IPV6] "The Hacker's Choice IPv6 Attack Toolkit",
	"SI6 Networks' IPv6 toolkit",		<http://www.thc.org/thc-ipv6/>.
	<http://www.si6networks.com/tools/ipv6toolkit>.
	[THC-IPV6]		[rafixd] "rafixd", <http://www.kame.net/dev/cvsweb2.cgi/kame/
	"The Hacker's Choice IPv6 Attack Toolkit",		kame/kame/rafixd/>.
	<http://www.thc.org/thc-ipv6/>.
	Appendix A. Assessment tools		[ramond] "ramond", <http://ramond.sourceforge.net/>.
	[SI6-IPv6] is a publicly-available set of tools (for Linux, *BSD, and		Appendix A. Assessment Tools
			[SI6-IPv6] is a publicly available set of tools (for Linux, *BSD, and
	Mac OS) that implements the techniques described in this document.		Mac OS) that implements the techniques described in this document.
	[THC-IPV6] is a publicly-available set of tools (for Linux) that		[THC-IPV6] is a publicly available set of tools (for Linux) that
	implements some of the techniques described in this document.		implements some of the techniques described in this document.
	Author's Address		Author's Address
	Fernando Gont		Fernando Gont
	Centre for the Protection of National Infrastructure		Huawei Technologies
			Evaristo Carriego 2644
			Haedo, Provincia de Buenos Aires 1706
			Argentina
	Email: fgont@si6networks.com		Phone: +54 11 4650 8472
	URI: http://www.cpni.gov.uk		EMail: fgont@si6networks.com
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