< draft-ietf-6man-segment-routing-header-13.txt		draft-ietf-6man-segment-routing-header-14.txt >
	Network Working Group S. Previdi		Network Working Group C. Filsfils, Ed.
	Internet-Draft Individual		Internet-Draft Cisco Systems, Inc.
	Intended status: Standards Track C. Filsfils, Ed.		Intended status: Standards Track S. Previdi
	Expires: November 24, 2018 Cisco Systems, Inc.		Expires: December 30, 2018 Individual
	J. Leddy		J. Leddy
	Comcast		Comcast
	S. Matsushima		S. Matsushima
	Softbank		Softbank
	D. Voyer, Ed.		D. Voyer, Ed.
	Bell Canada		Bell Canada
	May 23, 2018		June 28, 2018
	IPv6 Segment Routing Header (SRH)		IPv6 Segment Routing Header (SRH)
	draft-ietf-6man-segment-routing-header-13		draft-ietf-6man-segment-routing-header-14
	Abstract		Abstract
	Segment Routing can be applied to the IPv6 data plane using a new		Segment Routing can be applied to the IPv6 data plane using a new
	type of Routing Extension Header. This document describes the		type of Routing Extension Header. This document describes the
	Segment Routing Extension Header and how it is used by Segment		Segment Routing Extension Header and how it is used by Segment
	Routing capable nodes.		Routing capable nodes.
	Requirements Language		Requirements Language
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	document are to be interpreted as described in RFC 2119 [RFC2119].		"OPTIONAL" in this document are to be interpreted as described in BCP
			14 [RFC2119] [RFC8174] when, and only when, they appear in all
			capitals, as shown here.
	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 November 24, 2018.		This Internet-Draft will expire on December 30, 2018.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 25 ¶		skipping to change at page 2, line 25 ¶
	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 . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Segment Routing Extension Header . . . . . . . . . . . . . . 4		2. Segment Routing Extension Header . . . . . . . . . . . . . . 4
	2.1. SRH TLVs . . . . . . . . . . . . . . . . . . . . . . . . 5		2.1. SRH TLVs . . . . . . . . . . . . . . . . . . . . . . . . 5
	2.1.1. Padding TLVs . . . . . . . . . . . . . . . . . . . . 7		2.1.1. Padding TLVs . . . . . . . . . . . . . . . . . . . . 6
	2.1.2. HMAC TLV . . . . . . . . . . . . . . . . . . . . . . 8		2.1.2. HMAC TLV . . . . . . . . . . . . . . . . . . . . . . 8
	3. SR Nodes . . . . . . . . . . . . . . . . . . . . . . . . . . 9		3. SR Nodes . . . . . . . . . . . . . . . . . . . . . . . . . . 9
	3.1. Source SR Node . . . . . . . . . . . . . . . . . . . . . 9		3.1. Source SR Node . . . . . . . . . . . . . . . . . . . . . 9
	3.2. Transit Node . . . . . . . . . . . . . . . . . . . . . . 9		3.2. Transit Node . . . . . . . . . . . . . . . . . . . . . . 9
	3.3. SR Segment Endpoint Node . . . . . . . . . . . . . . . . 10		3.3. SR Segment Endpoint Node . . . . . . . . . . . . . . . . 9
	4. Packet Processing . . . . . . . . . . . . . . . . . . . . . . 10		4. Packet Processing . . . . . . . . . . . . . . . . . . . . . . 9
	4.1. Source SR Node . . . . . . . . . . . . . . . . . . . . . 10		4.1. Source SR Node . . . . . . . . . . . . . . . . . . . . . 9
	4.1.1. Reduced SRH . . . . . . . . . . . . . . . . . . . . . 10		4.1.1. Reduced SRH . . . . . . . . . . . . . . . . . . . . . 10
	4.2. Transit Node . . . . . . . . . . . . . . . . . . . . . . 11		4.2. Transit Node . . . . . . . . . . . . . . . . . . . . . . 10
	4.3. Segment Endpoint Node . . . . . . . . . . . . . . . . . . 11		4.3. SR Segment Endpoint Node . . . . . . . . . . . . . . . . 11
	4.3.1. FIB Entry Is Locally Instantiated SRv6 END SID . . . 11		4.3.1. FIB Entry Is Locally Instantiated SRv6 END SID . . . 11
	4.3.2. FIB Entry is a Local Interface . . . . . . . . . . . 12		4.3.2. FIB Entry is a Local Interface . . . . . . . . . . . 13
	4.3.3. FIB Entry Is A Non-Local Route . . . . . . . . . . . 13		4.3.3. FIB Entry Is A Non-Local Route . . . . . . . . . . . 13
	4.3.4. FIB Entry Is A No Match . . . . . . . . . . . . . . . 13		4.3.4. FIB Entry Is A No Match . . . . . . . . . . . . . . . 13
	4.4. Load Balancing and ECMP . . . . . . . . . . . . . . . . . 13		4.3.5. Load Balancing and ECMP . . . . . . . . . . . . . . . 13
	5. Illustrations . . . . . . . . . . . . . . . . . . . . . . . . 13		5. Illustrations . . . . . . . . . . . . . . . . . . . . . . . . 14
	5.1. Abstract Representation of an SRH . . . . . . . . . . . . 13		5.1. Abstract Representation of an SRH . . . . . . . . . . . . 14
	5.2. Example Topology . . . . . . . . . . . . . . . . . . . . 14		5.2. Example Topology . . . . . . . . . . . . . . . . . . . . 15
	5.3. Source SR Node . . . . . . . . . . . . . . . . . . . . . 15		5.3. Source SR Node . . . . . . . . . . . . . . . . . . . . . 15
	5.3.1. Intra SR Domain Packet . . . . . . . . . . . . . . . 15		5.3.1. Intra SR Domain Packet . . . . . . . . . . . . . . . 15
	5.3.2. Transit Packet Through SR Domain . . . . . . . . . . 15		5.3.2. Transit Packet Through SR Domain . . . . . . . . . . 16
	5.4. Transit Node . . . . . . . . . . . . . . . . . . . . . . 15		5.4. Transit Node . . . . . . . . . . . . . . . . . . . . . . 16
	5.5. SR End Node . . . . . . . . . . . . . . . . . . . . . . . 16		5.5. SR Segment Endpoint Node . . . . . . . . . . . . . . . . 16
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 16		6. Security Considerations . . . . . . . . . . . . . . . . . . . 17
	6.1. Threat model . . . . . . . . . . . . . . . . . . . . . . 17		6.1. Threat model . . . . . . . . . . . . . . . . . . . . . . 17
	6.1.1. Source routing threats . . . . . . . . . . . . . . . 17		6.1.1. Source routing threats . . . . . . . . . . . . . . . 17
	6.1.2. Applicability of RFC 5095 to SRH . . . . . . . . . . 17		6.1.2. Applicability of RFC 5095 to SRH . . . . . . . . . . 18
	6.1.3. Service stealing threat . . . . . . . . . . . . . . . 18		6.1.3. Service stealing threat . . . . . . . . . . . . . . . 19
	6.1.4. Topology disclosure . . . . . . . . . . . . . . . . . 18		6.1.4. Topology disclosure . . . . . . . . . . . . . . . . . 19
	6.1.5. ICMP Generation . . . . . . . . . . . . . . . . . . . 18		6.1.5. ICMP Generation . . . . . . . . . . . . . . . . . . . 19
	6.2. Security fields in SRH . . . . . . . . . . . . . . . . . 19		6.2. Security fields in SRH . . . . . . . . . . . . . . . . . 19
	6.2.1. Selecting a hash algorithm . . . . . . . . . . . . . 20		6.2.1. Selecting a hash algorithm . . . . . . . . . . . . . 21
	6.2.2. Performance impact of HMAC . . . . . . . . . . . . . 20		6.2.2. Performance impact of HMAC . . . . . . . . . . . . . 21
	6.2.3. Pre-shared key management . . . . . . . . . . . . . . 21		6.2.3. Pre-shared key management . . . . . . . . . . . . . . 22
	6.3. Deployment Models . . . . . . . . . . . . . . . . . . . . 22		6.3. Deployment Models . . . . . . . . . . . . . . . . . . . . 22
	6.3.1. Nodes within the SR domain . . . . . . . . . . . . . 22		6.3.1. Nodes within the SR domain . . . . . . . . . . . . . 22
	6.3.2. Nodes outside of the SR domain . . . . . . . . . . . 22		6.3.2. Nodes outside of the SR domain . . . . . . . . . . . 22
	6.3.3. SR path exposure . . . . . . . . . . . . . . . . . . 23		6.3.3. SR path exposure . . . . . . . . . . . . . . . . . . 23
	6.3.4. Impact of BCP-38 . . . . . . . . . . . . . . . . . . 23		6.3.4. Impact of BCP-38 . . . . . . . . . . . . . . . . . . 23
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
	7.1. Segment Routing Header Flags Register . . . . . . . . . . 24		7.1. Segment Routing Header Flags Register . . . . . . . . . . 24
	7.2. Segment Routing Header TLVs Register . . . . . . . . . . 24		7.2. Segment Routing Header TLVs Register . . . . . . . . . . 24
	8. Implementation Status . . . . . . . . . . . . . . . . . . . . 24		8. Implementation Status . . . . . . . . . . . . . . . . . . . . 25
	8.1. Linux . . . . . . . . . . . . . . . . . . . . . . . . . . 24		8.1. Linux . . . . . . . . . . . . . . . . . . . . . . . . . . 25
	8.2. Cisco Systems . . . . . . . . . . . . . . . . . . . . . . 25		8.2. Cisco Systems . . . . . . . . . . . . . . . . . . . . . . 25
	8.3. FD.io . . . . . . . . . . . . . . . . . . . . . . . . . . 25		8.3. FD.io . . . . . . . . . . . . . . . . . . . . . . . . . . 25
	8.4. Barefoot . . . . . . . . . . . . . . . . . . . . . . . . 25		8.4. Barefoot . . . . . . . . . . . . . . . . . . . . . . . . 25
	8.5. Juniper . . . . . . . . . . . . . . . . . . . . . . . . . 25		8.5. Juniper . . . . . . . . . . . . . . . . . . . . . . . . . 26
	9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25		9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 26
	10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26		10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 26		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
	11.1. Normative References . . . . . . . . . . . . . . . . . . 26		11.1. Normative References . . . . . . . . . . . . . . . . . . 26
	11.2. Informative References . . . . . . . . . . . . . . . . . 27		11.2. Informative References . . . . . . . . . . . . . . . . . 27
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
	1. Introduction		1. Introduction
	Segment Routing can be applied to the IPv6 data plane using a new		Segment Routing can be applied to the IPv6 data plane using a new
	type of Routing Extension Header (SRH). This document describes the		type of Routing Extension Header (SRH). This document describes the
	Segment Routing Extension Header and how it is used by Segment		Segment Routing Extension Header and how it is used by Segment
	Routing capable nodes.		Routing capable nodes.
	The Segment Routing Architecture [I-D.ietf-spring-segment-routing]		The Segment Routing Architecture [I-D.ietf-spring-segment-routing]
	describes Segment Routing and its instantiation in two data planes		describes Segment Routing and its instantiation in two data planes
	skipping to change at page 4, line 5 ¶		skipping to change at page 4, line 5 ¶
	SR with the MPLS data plane is defined in		SR with the MPLS data plane is defined in
	[I-D.ietf-spring-segment-routing-mpls].		[I-D.ietf-spring-segment-routing-mpls].
	SR with the IPv6 data plane is defined in		SR with the IPv6 data plane is defined in
	[I-D.filsfils-spring-srv6-network-programming].		[I-D.filsfils-spring-srv6-network-programming].
	The encoding of MPLS labels and label stacking are defined in		The encoding of MPLS labels and label stacking are defined in
	[RFC3032].		[RFC3032].
	The encoding of IPv6 segments in the Segment Routing Extension header		The encoding of IPv6 segments in the Segment Routing Extension Header
	is defined in this document.		is defined in this document.
	Terminology used within this document is defined in detail in		Terminology used within this document is defined in detail in
	[I-D.ietf-spring-segment-routing]. Specifically, these terms:		[I-D.ietf-spring-segment-routing]. Specifically, these terms:
	Segment Routing, SR Domain, SRv6, Segment ID (SID), SRv6 SID, Active		Segment Routing, SR Domain, SRv6, Segment ID (SID), SRv6 SID, Active
	Segment, and SR Policy.		Segment, and SR Policy.
	2. Segment Routing Extension Header		2. Segment Routing Extension Header
	Routing Headers are defined in [RFC8200]. The Segment Routing Header		Routing Headers are defined in [RFC8200]. The Segment Routing Header
	skipping to change at page 5, line 17 ¶		skipping to change at page 5, line 17 ¶
	o Segments Left: Defined in [RFC8200]		o Segments Left: Defined in [RFC8200]
	o Last Entry: contains the index (zero based), in the Segment List,		o Last Entry: contains the index (zero based), in the Segment List,
	of the last element of the Segment List.		of the last element of the Segment List.
	o Flags: 8 bits of flags. Following flags are defined:		o Flags: 8 bits of flags. Following flags are defined:
	0 1 2 3 4 5 6 7		0 1 2 3 4 5 6 7
	+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+
	| U |H| U |		|U U U U U U U U|
	+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+
	U: Unused and for future use. SHOULD be 0 on transmission and		U: Unused and for future use. MUST be 0 on transmission and
	MUST be ignored on receipt.		ignored on receipt.
	H-flag: HMAC flag. If set, the HMAC TLV is present and is
	encoded as the last TLV of the SRH. In other words, the last
	36 octets of the SRH represent the HMAC information. See
	Section 2.1.2 for details on the HMAC TLV.
	o Tag: tag a packet as part of a class or group of packets, e.g.,		o Tag: tag a packet as part of a class or group of packets, e.g.,
	packets sharing the same set of properties. When tag is not used		packets sharing the same set of properties. When tag is not used
	at source it SHOULD be set to zero on transmission. When tag is		at source it MUST be set to zero on transmission. When tag is not
	not used during SRH Processing it MUST be ignored. The allocation		used during SRH Processing it SHOULD be ignored. The allocation
	and use of tag is outside the scope of this document.		and use of tag is outside the scope of this document.
	o Segment List[n]: 128 bit IPv6 addresses representing the nth		o Segment List[n]: 128 bit IPv6 addresses representing the nth
	segment in the Segment List. The Segment List is encoded starting		segment in the Segment List. The Segment List is encoded starting
	from the last segment of the SR Policy. I.e., the first element		from the last segment of the SR Policy. I.e., the first element
	of the segment list (Segment List [0]) contains the last segment		of the segment list (Segment List [0]) contains the last segment
	of the SR Policy, the second element contains the penultimate		of the SR Policy, the second element contains the penultimate
	segment of the SR Policy and so on.		segment of the SR Policy and so on.
	o Type Length Value (TLV) are described in Section 2.1.		o Type Length Value (TLV) are described in Section 2.1.
	skipping to change at page 6, line 20 ¶		skipping to change at page 6, line 12 ¶
	Type: An 8 bit value. Unrecognized Types MUST be ignored on receipt.		Type: An 8 bit value. Unrecognized Types MUST be ignored on receipt.
	Length: The length of the Variable length data. It is RECOMMENDED		Length: The length of the Variable length data. It is RECOMMENDED
	that the total length of new TLVs be multiple of 8 bytes to avoid the		that the total length of new TLVs be multiple of 8 bytes to avoid the
	use of Padding TLVs.		use of Padding TLVs.
	Variable length data: Length bytes of data that is specific to the		Variable length data: Length bytes of data that is specific to the
	Type.		Type.
	Type Length Value (TLV) contain optional information that may be used		Type Length Value (TLV) contain OPTIONAL information that may be used
	by the node identified in the Destination Address (DA) of the packet.		by the node identified in the Destination Address (DA) of the packet.
	The information carried in the TLVs is not intended to be used by the
	routing layer. Typically, TLVs carry information that is consumed by
	other components (e.g.: OAM) than the routing function.
	Each TLV has its own length, format and semantic. The code-point		Each TLV has its own length, format and semantic. The code-point
	allocated (by IANA) to each TLV Type defines both the format and the		allocated (by IANA) to each TLV Type defines both the format and the
	semantic of the information carried in the TLV. Multiple TLVs may be		semantic of the information carried in the TLV. Multiple TLVs may be
	encoded in the same SRH.		encoded in the same SRH.
	TLVs may change en route at each segment. To identify when a TLV		TLVs may change en route at each segment. To identify when a TLV
	type may change en route the most significant bit of the Type has the		type may change en route the most significant bit of the Type has the
	following significance:		following significance:
	skipping to change at page 7, line 16 ¶		skipping to change at page 7, line 5 ¶
	HMAC TLV		HMAC TLV
	Additional TLVs may be defined in the future.		Additional TLVs may be defined in the future.
	2.1.1. Padding TLVs		2.1.1. Padding TLVs
	There are two types of padding TLVs, pad0 and padN, the following		There are two types of padding TLVs, pad0 and padN, the following
	applies to both:		applies to both:
	Padding TLVs are optional and more than one Padding TLV MUST NOT		Padding TLVs are used to pad the TLVs to a multiple of 8 octets.
	appear in the SRH.
			More than one Padding TLV MUST NOT appear in the SRH.
	The Padding TLVs are used to align the SRH total length on the 8		The Padding TLVs are used to align the SRH total length on the 8
	octet boundary.		octet boundary.
	When present, a single Pad0 or PadN TLV MUST appear as the last		When present, a single Pad0 or PadN TLV MUST appear as the last
	TLV before the HMAC TLV (if HMAC TLV is present).		TLV.
	When present, a PadN TLV MUST have a length from 0 to 5 in order		When present, a PadN TLV MUST have a length from 0 to 5 in order
	to align the SRH total length on a 8-octet boundary.		to align the SRH total length on a 8-octet boundary.
	Padding TLVs are ignored by a node processing the SRH TLV, even if		Padding TLVs are ignored by a node processing the SRH TLV, even if
	more than one is present.		more than one is present.
	Padding TLVs are ignored during ICV calculation.		Padding TLVs are ignored during ICV calculation.
	2.1.1.1. PAD0		2.1.1.1. PAD0
	skipping to change at page 8, line 4 ¶		skipping to change at page 7, line 37 ¶
	| Type |		| Type |
	+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+
	Type: to be assigned by IANA (Suggested value 128)		Type: to be assigned by IANA (Suggested value 128)
	A single Pad0 TLV MUST be used when a single byte of padding is		A single Pad0 TLV MUST be used when a single byte of padding is
	required. If more than one byte of padding is required a Pad0 TLV		required. If more than one byte of padding is required a Pad0 TLV
	MUST NOT be used, the PadN TLV MUST be used.		MUST NOT be used, the PadN TLV MUST be used.
	2.1.1.2. PADN		2.1.1.2. PADN
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length | Padding (variable) |		| Type | Length | Padding (variable) |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	// Padding (variable) //		// Padding (variable) //
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Type: to be assigned by IANA (suggested value 129).		Type: to be assigned by IANA (suggested value 129).
	Length: 0 to 5		Length: 0 to 5
	Padding: Length octets of padding. Padding bits have no		Padding: Length octets of padding. Padding bits have no
	semantics. They SHOULD be set to 0 on transmission and MUST be		semantics. They MUST be set to 0 on transmission and ignored on
	ignored on receipt.		receipt.
	The PadN TLV MUST be used when more than one byte of padding is		The PadN TLV MUST be used when more than one byte of padding is
	required.		required.
	2.1.2. HMAC TLV		2.1.2. HMAC TLV
	HMAC TLV is optional and contains the HMAC information. The HMAC TLV		HMAC TLV is OPTIONAL and contains the HMAC information. The HMAC TLV
	has the following format:		has the following format:
	0 1 2 3		0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Length | RESERVED |		| Type | Length | RESERVED |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| HMAC Key ID (4 octets) |		| HMAC Key ID (4 octets) |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| //		| //
	| HMAC (32 octets) //		| HMAC (32 octets) //
	| //		| //
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	where:		where:
	o Type: to be assigned by IANA (suggested value 5).		o Type: to be assigned by IANA (suggested value 5).
	o Length: 38.		o Length: 38.
	o RESERVED: 2 octets. SHOULD be unset on transmission and MUST be		o RESERVED: 2 octets. MUST be 0 on transmission and ignored on
	ignored on receipt.		receipt.
	o HMAC Key ID: 4 octets.		o HMAC Key ID: 4 octets.
	o HMAC: 32 octets.		o HMAC: 32 octets.
	o HMAC and HMAC Key ID usage is described in Section 6		o HMAC and HMAC Key ID usage is described in Section 6
	The Following applies to the HMAC TLV:		The Following applies to the HMAC TLV:
	o When present, the HMAC TLV MUST be encoded as the last TLV of the		o Local policy determines when to check for an HMAC and potentially
	SRH.		a requirement on where the HMAC TLV must appear (e.g. first TLV).
			This local policy is outside the scope of this document. It may
	o If the HMAC TLV is present, the SRH H-Flag (Figure 2) MUST be set.		be based on the active segment at an SR Segment endpoint node, the
	Nodes processing SRH SHOULD process the HMAC TLV only when the		result of an ACL that considers incoming interface, or other
	H-Flag is set, and local policy.		packet fields.
	o When the H-flag is set in the SRH, the router inspecting the SRH
	MUST find the HMAC TLV in the last 38 octets of the SRH.
	3. SR Nodes		3. SR Nodes
	There are different types of nodes that may be involved in segment		There are different types of nodes that may be involved in segment
	routing networks: source SR nodes originate packets with a segment in		routing networks: source SR nodes originate packets with a segment in
	the destination address of the IPv6 header, transit nodes that		the destination address of the IPv6 header, transit nodes that
	forward packets destined to a remote segment, and segment endpoint		forward packets destined to a remote segment, and SR segment endpoint
	nodes that process a local segment in the destination address of an		nodes that process a local segment in the destination address of an
	IPv6 header.		IPv6 header.
	3.1. Source SR Node		3.1. Source SR Node
	A Source SR Node is any node that originates an IPv6 packet with a		A Source SR Node is any node that originates an IPv6 packet with a
	segment (i.e. SRv6 SID) in the destination address of the IPv6		segment (i.e. SRv6 SID) in the destination address of the IPv6
	header. The packet leaving the source SR Node may or may not contain		header. The packet leaving the source SR Node may or may not contain
	an SRH. This includes either:		an SRH. This includes either:
	A host originating an IPv6 packet.		A host originating an IPv6 packet.
	An SR domain ingress router encapsulating a received packet in an		An SR domain ingress router encapsulating a received packet in an
	outer IPv6 header, followed by an optional SRH.		outer IPv6 header, followed by an optional SRH.
	The mechanism through which a segment in the destination address of		The mechanism through which a segment in the destination address of
	the IPv6 header and the Segment List in the SRH, is derived is		the IPv6 header and the Segment List in the SRH, is derived is
	outside the scope of this document. For example, the Segment List		outside the scope of this document.
	may be obtained through local SR Policy computation, local
	configuration, interaction with a controller instantiating an SR
	Policy, or any other mechanism.
	3.2. Transit Node		3.2. Transit Node
	A transit node is any node forwarding an IPv6 packet where the		A transit node is any node forwarding an IPv6 packet where the
	destination address of that packet is not locally configured as a		destination address of that packet is not locally configured as a
	segment nor a local interface. A transit node is not required to be		segment nor a local interface. A transit node is not required to be
	capable of processing a segment nor SRH.		capable of processing a segment nor SRH.
	3.3. SR Segment Endpoint Node		3.3. SR Segment Endpoint Node
	A SR segment endpoint node is any node receiving an IPv6 packet where		A SR segment endpoint node is any node receiving an IPv6 packet where
	the destination address of that packet is locally configured as a		the destination address of that packet is locally configured as a
	segment or local interface.		segment or local interface.
	4. Packet Processing		4. Packet Processing
	This section describes SRv6 packet processing at the Source, Transit		This section describes SRv6 packet processing at the SR source,
	and Segment Endpoint nodes.		Transit and SR segment endpoint nodes.
	4.1. Source SR Node		4.1. Source SR Node
	A Source node steers a packet into an SR Policy and the SRH is		A Source node steers a packet into an SR Policy. If the SR Policy
	created as follows:		results in a segment list containing a single segment, and there is
			no need to add information to SRH flag or TLV, the DA is set to the
			single segment list entry and the SRH MAY be omitted.
			When needed, the SRH is created as follows:
	Next Header and Hdr Ext Len fields are set as specified in		Next Header and Hdr Ext Len fields are set as specified in
	[RFC8200].		[RFC8200].
	Routing Type field is set as TBD (to be allocated by IANA,		Routing Type field is set as TBD (to be allocated by IANA,
	suggested value 4).		suggested value 4).
	The DA of the packet is set with the value of the first segment.		The DA of the packet is set with the value of the first segment.
	The first element of the SRH Segment List is the ultimate segment.		The first element of the SRH Segment List is the ultimate segment.
	The second element is the penultimate segment and so on.		The second element is the penultimate segment and so on.
	The Segments Left field is set to n-1 where n is the number of		The Segments Left field is set to n-1 where n is the number of
	elements in the SR Policy.		elements in the SR Policy.
	The Last Entry field is set to n-1 where n is the number of		The Last Entry field is set to n-1 where n is the number of
	elements in the SR Policy.		elements in the SR Policy.
	HMAC TLV may be set according to Section 6.		HMAC TLV may be set according to Section 6.
	If the segment list contains a single segment and there is no need
	for information in flag or TLV, then the SRH MAY be omitted.
	The packet is forwarded toward the packet's Destination Address		The packet is forwarded toward the packet's Destination Address
	(the first segment).		(the first segment).
	4.1.1. Reduced SRH		4.1.1. Reduced SRH
	When a source does not require the entire SID list to be preserved in		When a source does not require the entire SID list to be preserved in
	the SRH, a reduced SRH may be used.		the SRH, a reduced SRH may be used.
	A reduced SRH does not contain the first segment of the related SR		A reduced SRH does not contain the first segment of the related SR
	Policy (the first segment is the one already in the DA of the IPv6		Policy (the first segment is the one already in the DA of the IPv6
	skipping to change at page 11, line 22 ¶		skipping to change at page 11, line 8 ¶
	NOT inspect the underneath routing header and MUST forward the packet		NOT inspect the underneath routing header and MUST forward the packet
	toward the DA according to its IPv6 routing table.		toward the DA according to its IPv6 routing table.
	When a SID is in the destination address of an IPv6 header of a		When a SID is in the destination address of an IPv6 header of a
	packet, it's routed through an IPv6 network as an IPv6 address.		packet, it's routed through an IPv6 network as an IPv6 address.
	SIDs, or the prefix(es) covering SIDs, and their reachability may be		SIDs, or the prefix(es) covering SIDs, and their reachability may be
	distributed by means outside the scope of this document. For		distributed by means outside the scope of this document. For
	example, [RFC5308] or [RFC5340] may be used to advertise a prefix		example, [RFC5308] or [RFC5340] may be used to advertise a prefix
	covering the SIDs on a node.		covering the SIDs on a node.
	4.3. Segment Endpoint Node		4.3. SR Segment Endpoint Node
	Without constraining the details of an implementation, the Segment		Without constraining the details of an implementation, the SR segment
	Endpoint Node creates Forwarding Information Base (FIB) entries for		endpoint node creates Forwarding Information Base (FIB) entries for
	its local SIDs.		its local SIDs.
	When an SRv6-capable node receives an IPv6 packet, it performs a		When an SRv6-capable node receives an IPv6 packet, it performs a
	longest-prefix-match lookup on the packets destination address. This		longest-prefix-match lookup on the packets destination address. This
	lookup can return any of the following:		lookup can return any of the following:
	A FIB entry that represents a locally instantiated SRv6 SID		A FIB entry that represents a locally instantiated SRv6 SID
	A FIB entry that represents a local interface, not locally		A FIB entry that represents a local interface, not locally
	instantiated as an SRv6 SID		instantiated as an SRv6 SID
	A FIB entry that represents a non-local route		A FIB entry that represents a non-local route
	No Match		No Match
	4.3.1. FIB Entry Is Locally Instantiated SRv6 END SID		4.3.1. FIB Entry Is Locally Instantiated SRv6 END SID
	This document, and section, defines a single SRv6 SID called END.		This document, and section, defines a single SRv6 SID called END.
	Future documents may define additional SRv6 SIDs. In which case, the		Future documents may define additional SRv6 SIDs. In which case, the
	entire content of this section will be defined in that document.		entire content of this section will be defined in that document.
	If the FIB entry represents a locally instantiated SRv6 SID, process		If the FIB entry represents a locally instantiated SRv6 SID, process
	the next header of the IPv6 header as defined in section 4 of		the next header of the IPv6 header as defined in section 4 of
	[RFC8200] until the upper-layer header, or "No Next Header" is		[RFC8200]
	reached.
			The following sections describe the actions to take while processing
			next header fields.
			4.3.1.1. SRH Processing
	When an SRH is processed {		When an SRH is processed {
	If Segments Left is equal to zero {		If Segments Left is equal to zero {
	Skip SRH Processing		Proceed to process the next header in the packet, whose type
			is identified by the Next Header field in the Routing header.
	}		}
	Else {		Else {
	If Segments Left is greater than (Last Entry+1) {		If local policy requires TLV processing {
			Perform TLV processing (see TLV Processing)
			}
			max_last_entry = ( Hdr Ext Len / 2 ) - 1
			If ((Last Entry > max_last_entry) or
			(Segments Left is greater than (Last Entry+1)) {
	Send an ICMP Parameter Problem, Code 0, message to the		Send an ICMP Parameter Problem, Code 0, message to the
	Source Address, pointing to the Segments Left field, and		Source Address, pointing to the Segments Left field, and
	discard the packet.		discard the packet.
	}		}
	Else {		Else {
	Decrement Segments Left by 1.		Decrement Segments Left by 1.
	Copy Segment List[Segments Left] from the SRH to the		Copy Segment List[Segments Left] from the SRH to the
	destination address of the IPv6 header.		destination address of the IPv6 header.
	If the IPv6 Hop Limit is less than or equal to 1 {		If the IPv6 Hop Limit is less than or equal to 1 {
	Send an ICMP Time Exceeded -- Hop Limit Exceeded in		Send an ICMP Time Exceeded -- Hop Limit Exceeded in
	skipping to change at page 12, line 33 ¶		skipping to change at page 12, line 39 ¶
	}		}
	Else {		Else {
	Decrement the Hop Limit by 1		Decrement the Hop Limit by 1
	Resubmit the packet to the IPv6 module for transmission		Resubmit the packet to the IPv6 module for transmission
	to the new destination.		to the new destination.
	}		}
	}		}
	}		}
	}		}
	If the upper-layer header or No Next Header is reached {		4.3.1.1.1. TLV Processing
			Local policy determines how TLV's are to be processed when the Active
			Segment is a local END SID. The definition of local policy is
			outside the scope of this document.
			For illustration purpose only, two example local policies that may be
			associated with an END SID are provided below.
			Example 1:
			For any packet received from interface I2
			Skip TLV processing
			Example 2:
			For any packet received from interface I1
			If first TLV is HMAC {
			Process the HMAC TLV
			}
			Else {
			Discard the packet
			}
			4.3.1.2. Upper-layer Header or No Next Header
	Send an ICMP destination unreachable to		Send an ICMP destination unreachable to
	the Source Address and discard the packet.		the Source Address and discard the packet.
	}
	4.3.2. FIB Entry is a Local Interface		4.3.2. FIB Entry is a Local Interface
	If the FIB entry represents a local interface, not locally		If the FIB entry represents a local interface, not locally
	instantiated as an SRv6 SID, the SRH is processed as follows:		instantiated as an SRv6 SID, the SRH is processed as follows:
	If Segments Left is zero, the node must ignore the Routing header		If Segments Left is zero, the node must ignore the Routing header
	and proceed to process the next header in the packet, whose type		and proceed to process the next header in the packet, whose type
	is identified by the Next Header field in the Routing header.		is identified by the Next Header field in the Routing Header.
	If Segments Left is non-zero, the node must discard the packet and		If Segments Left is non-zero, the node must discard the packet and
	send an ICMP Parameter Problem, Code 0, message to the packet's		send an ICMP Parameter Problem, Code 0, message to the packet's
	Source Address, pointing to the unrecognized Routing Type.		Source Address, pointing to the unrecognized Routing Type.
	4.3.3. FIB Entry Is A Non-Local Route		4.3.3. FIB Entry Is A Non-Local Route
	Processing is not changed by this document.		Processing is not changed by this document.
	4.3.4. FIB Entry Is A No Match		4.3.4. FIB Entry Is A No Match
	Processing is not changed by this document.		Processing is not changed by this document.
	4.4. Load Balancing and ECMP		4.3.5. Load Balancing and ECMP
	Within an SR domain, an SR source node encapsulates a packet in an		Within an SR domain, an SR source node encapsulates a packet in an
	outer IPv6 header for transport to an endpoint. The SR source node		outer IPv6 header for transport to an endpoint. The SR source node
	MUST impose a flow label computed based on the inner packet. The		MUST impose a flow label computed based on the inner packet. The
	computation of the flow label is as recommended in [RFC6438] for the		computation of the flow label is as recommended in [RFC6438] for the
	sending Tunnel End Point.		sending Tunnel End Point.
	At any transit node within an SR domain, the flow label MUST be used		At any transit node within an SR domain, the flow label MUST be used
	as defined in [RFC6438] to calculate the ECMP hash toward the		as defined in [RFC6438] to calculate the ECMP hash toward the
	destination address. If flow label is not used, the transit node may		destination address. If flow label is not used, the transit node may
	hash all packets between a pair of SR Edge nodes to the same link.		hash all packets between a pair of SR Edge nodes to the same link.
	At an SR segment endpoint node, the flow label MUST be used as		At an SR segment endpoint node, the flow label MUST be used as
	defined in [RFC6438] to calculate any ECMP hash used to forward the		defined in [RFC6438] to calculate any ECMP hash used to forward the
	processed packet to the next segment.		processed packet to the next segment.
	5. Illustrations		5. Illustrations
	This section provides illustrations of SRv6 packet processing at		This section provides illustrations of SRv6 packet processing at SR
	source, transit and endpoint nodes.		source, transit and SR segment endpoint nodes.
	5.1. Abstract Representation of an SRH		5.1. Abstract Representation of an SRH
	For a node k, its IPv6 address is represented as Ak, its SRv6 SID is		For a node k, its IPv6 address is represented as Ak, its SRv6 SID is
	represented as Sk.		represented as Sk.
	IPv6 headers are represented as the tuple of (source, destination).		IPv6 headers are represented as the tuple of (source, destination).
	For example, a packet with source address A1 and destination address		For example, a packet with source address A1 and destination address
	A2 is represented as (A1,A2). The payload of the packet is omitted.		A2 is represented as (A1,A2). The payload of the packet is omitted.
	skipping to change at page 16, line 4 ¶		skipping to change at page 16, line 38 ¶
	a reduced SRH, Router 3 encapsulates the received packet P3 in an		a reduced SRH, Router 3 encapsulates the received packet P3 in an
	outer header with a reduced SRH. The packet is		outer header with a reduced SRH. The packet is
	P6: (A3, S7)(S4; SL=1)(A1, A2)		P6: (A3, S7)(S4; SL=1)(A1, A2)
	5.4. Transit Node		5.4. Transit Node
	Nodes 5 acts as transit nodes for packet P1, and sends packet		Nodes 5 acts as transit nodes for packet P1, and sends packet
	P1: (A8,S7)(A9,S7;SL=1)		P1: (A8,S7)(A9,S7;SL=1)
	on the interface toward node 7.		on the interface toward node 7.
	5.5. SR End Node		5.5. SR Segment Endpoint Node
	Node 7 receives packet P1 and, using the logic in section 4.3.1,		Node 7 receives packet P1 and, using the logic in section 4.3.1,
	sends packet		sends packet
	P7: (A8,A9)(A9,S7; SL=0)		P7: (A8,A9)(A9,S7; SL=0)
	on the interface toward router 6.		on the interface toward router 6.
	6. Security Considerations		6. Security Considerations
	This section analyzes the security threat model, the security issues		This section analyzes the security threat model, the security issues
	and proposed solutions related to the new Segment Routing Header.		and proposed solutions related to the new Segment Routing Header.
	The Segment Routing Header (SRH) is simply another type of the		The Segment Routing Header (SRH) is simply another type of the
	routing header as described in [RFC8200] and is:		Routing Header as described in [RFC8200] and is:
	o Added by an SR edge router when entering the segment routing		o Added by an SR edge router when entering the segment routing
	domain or by the originating host itself. The source host can		domain or by the originating host itself. The source host can
	even be outside the SR domain;		even be outside the SR domain;
	o inspected and acted upon when reaching the destination address of		o inspected and acted upon when reaching the destination address of
	the IP header per [RFC8200].		the IP header per [RFC8200].
	Per [RFC8200], routers on the path that simply forward an IPv6 packet		Per [RFC8200], routers on the path that simply forward an IPv6 packet
	(i.e. the IPv6 destination address is none of theirs) will never		(i.e. the IPv6 destination address is none of theirs) will never
	inspect and process the content of the SRH. Routers whose FIB		inspect and process the content of the SRH. Routers whose FIB
	contains a locally instantiated SRv6 SID equal to the destination		contains a locally instantiated SRv6 SID equal to the destination
	address field of the IPv6 packet MUST parse the SRH and, if supported		address field of the IPv6 packet MUST parse the SRH if present, and
	and if the local configuration allows it, MUST act accordingly to the		if supported and if the local configuration allows it, MUST act
	SRH content.		accordingly to the SRH content.
	As specified in [RFC8200], the default behavior of a non SR-capable		As specified in [RFC8200], the default behavior of a non SR-capable
	router upon receipt of an IPv6 packet with SRH destined to an address		router upon receipt of an IPv6 packet with SRH destined to an address
	of its, is to:		of its, is to:
	o ignore the SRH completely if the Segment Left field is 0 and		o ignore the SRH completely if the Segment Left field is 0 and
	proceed to process the next header in the IPv6 packet;		proceed to process the next header in the IPv6 packet;
	o discard the IPv6 packet if Segment Left field is greater than 0,		o discard the IPv6 packet if Segment Left field is greater than 0,
	it MAY send a Parameter Problem ICMP message back to the Source		it MAY send a Parameter Problem ICMP message back to the Source
	skipping to change at page 18, line 40 ¶		skipping to change at page 19, line 26 ¶
	intercept packets containing SRH. On the other hand, if the attacker		intercept packets containing SRH. On the other hand, if the attacker
	can do a traceroute whose probes will be forwarded along the SR		can do a traceroute whose probes will be forwarded along the SR
	Policy, then there is little learned by intercepting the SRH itself.		Policy, then there is little learned by intercepting the SRH itself.
	6.1.5. ICMP Generation		6.1.5. ICMP Generation
	Per Section 4.4 of [RFC8200], when destination nodes (i.e. where the		Per Section 4.4 of [RFC8200], when destination nodes (i.e. where the
	destination address is one of theirs) receive a Routing Header with		destination address is one of theirs) receive a Routing Header with
	unsupported Routing Type, the required behavior is:		unsupported Routing Type, the required behavior is:
	o If Segments Left is zero, the node must ignore the Routing header		o If Segments Left is zero, the node must ignore the Routing Header
	and proceed to process the next header in the packet.		and proceed to process the next header in the packet.
	o If Segments Left is non-zero, the node must discard the packet and		o If Segments Left is non-zero, the node must discard the packet and
	send an ICMP Parameter Problem, Code 0, message to the packet's		send an ICMP Parameter Problem, Code 0, message to the packet's
	Source Address, pointing to the unrecognized Routing Type.		Source Address, pointing to the unrecognized Routing Type.
	This required behavior could be used by an attacker to force the		This required behavior could be used by an attacker to force the
	generation of ICMP message by any node. The attacker could send		generation of ICMP message by any node. The attacker could send
	packets with SRH (with Segment Left not set to 0) destined to a node		packets with SRH (with Segment Left not set to 0) destined to a node
	not supporting SRH. Per [RFC8200], the destination node could		not supporting SRH. Per [RFC8200], the destination node could
	skipping to change at page 20, line 50 ¶		skipping to change at page 21, line 36 ¶
	right-hand padded with 96 bits set to 0. The authors understand that		right-hand padded with 96 bits set to 0. The authors understand that
	this is not secure but is ok for limited tests.		this is not secure but is ok for limited tests.
	6.2.2. Performance impact of HMAC		6.2.2. Performance impact of HMAC
	While adding an HMAC to each and every SR packet increases the		While adding an HMAC to each and every SR packet increases the
	security, it has a performance impact. Nevertheless, it must be		security, it has a performance impact. Nevertheless, it must be
	noted that:		noted that:
	o the HMAC field is used only when SRH is added by a device (such as		o the HMAC field is used only when SRH is added by a device (such as
	a home set-up box) which is outside of the segment routing domain.		a home set-top box) which is outside of the segment routing
	If the SRH is added by a router in the trusted segment routing		domain. If the SRH is added by a router in the trusted segment
	domain, then, there is no need for an HMAC field, hence no		routing domain, then, there is no need for an HMAC field, hence no
	performance impact.		performance impact.
	o when present, the HMAC field MUST only be checked and validated by		o when present, the HMAC field need only be checked and validated by
	the first router of the segment routing domain, this router is		the first router of the segment routing domain, this router is
	named 'validating SR router'. Downstream routers may not inspect		named 'validating SR router'.
	the HMAC field.
	o this validating router can also have a cache of <IPv6 header +		o this validating SR router can also have a cache of <IPv6 header +
	SRH, HMAC field value> to improve the performance. It is not the		SRH, HMAC field value> to improve the performance. It is not the
	same use case as in IPsec where HMAC value was unique per packet,		same use case as in IPsec where HMAC value was unique per packet,
	in SRH, the HMAC value is unique per flow.		in SRH, the HMAC value is unique per flow.
	o Last point, hash functions such as SHA-2 have been optimized for		o hash functions such as SHA-2 have been optimized for security and
	security and performance and there are multiple implementations		performance and there are multiple implementations with good
	with good performance.		performance.
	With the above points in mind, the performance impact of using HMAC		With the above points in mind, the performance impact of using HMAC
	is minimized.		is minimized.
	6.2.3. Pre-shared key management		6.2.3. Pre-shared key management
	The field HMAC Key-id allows for:		The field HMAC Key-id allows for:
	o key roll-over: when there is a need to change the key (the hash		o key roll-over: when there is a need to change the key (the hash
	pre-shared secret), then multiple pre-shared keys can be used		pre-shared secret), then multiple pre-shared keys can be used
	simultaneously. The validating routing can have a table of <HMAC		simultaneously. The validating SR router can have a table of
	Key-id, pre-shared secret> for the currently active and future		<HMAC Key-id, pre-shared secret> for the currently active and
	keys.		future keys.
	o different algorithms: by extending the previous table to <HMAC		o different algorithms: by extending the previous table to <HMAC
	Key-id, hash function, pre-shared secret>, the validating router		Key-id, hash function, pre-shared secret>, the validating SR
	can also support simultaneously several hash algorithms (see		router can also support several hash algorithms (see section
	section Section 6.2.1)		Section 6.2.1)
	The pre-shared secret distribution can be done:		The pre-shared secret distribution can be done:
	o in the configuration of the validating routers, either by static		o in the configuration of the validating SR routers, either by
	configuration or any SDN oriented approach;		static configuration or any SDN oriented approach;
	o dynamically using a trusted key distribution such as [RFC6407]		o dynamically using a trusted key distribution such as [RFC6407]
	The intent of this document is NOT to define yet-another-key-		The intent of this document is NOT to define yet-another-key-
	distribution-protocol.		distribution-protocol.
	6.3. Deployment Models		6.3. Deployment Models
	6.3.1. Nodes within the SR domain		6.3.1. Nodes within the SR domain
	An SR domain is defined as a set of interconnected routers where all		SR Source Nodes within an SR Domain are trusted to generate IPv6
	routers at the perimeter are configured to add and act on SRH. Some		packets with SRH. SR segment endpoint nodes receiving packets on
	routers inside the SR domain can also act on SRH or simply forward		interface that are part of the SR Domain may process any packet
	IPv6 packets.		destined to a local segment, containing an SRH.
	The routers inside an SR domain can be trusted to generate SRH and to
	process SRH received on interfaces that are part of the SR domain.
	These nodes MUST drop all SRH packets received on an interface that
	is not part of the SR domain, destined to a locally instantiated SID,
	and containing an SRH whose HMAC field cannot be validated by local
	policies. This includes obviously packet with an SRH generated by a
	non-cooperative SR domain.
	If the validation fails, then these packets MUST be dropped, ICMP
	error messages (parameter problem) SHOULD be generated (but rate
	limited) and SHOULD be logged.
	6.3.2. Nodes outside of the SR domain		6.3.2. Nodes outside of the SR domain
	Nodes outside of the SR domain cannot be trusted for physical		Nodes outside the SR Domain cannot be trusted. SR Domain Ingress
	security; hence, they need to request by some trusted means (outside		routers SHOULD discard packets destined to SIDs within the SR Domain
	the scope of this document) a complete SRH for each new connection		(regardless of the presence of an SRH) to avoid attacks on the SR
	(i.e. new destination address). The received SRH MUST include an		Domain. This is accomplished via infrastructure Access Lists (iACLs)
	HMAC TLV which is computed correctly (see Section 6.2).		applied on domain ingress nodes. However the SR Domain may be
			extended to nodes outside of it via use of the SRH HMAC.
	When an outside node sends a packet with an SRH and towards an SR		Nodes outside the SR Domain may request, by some trusted means
	domain ingress node, the packet MUST contain the HMAC TLV (with a		outside the scope of this document, a complete SRH including an HMAC
	Key-id and HMAC fields) and the the destination address MUST be an		TLV which is computed correctly for the SRH (see Section 6.2).
	address of an SR domain ingress node .
	The ingress SR router, i.e., the router with a SID equal to the		SR Domain ingress routers permit traffic destined to select SIDs with
	destination address, MUST verify the HMAC TLV.		local policy requiring HMAC TLV processing for those select SIDs,
			i.e. these SIDs provide a gateway to the SR Domain for a set of
			segment lists.
	If the validation is successful, then the packet is simply forwarded		If HMAC validation is successful, the packet is forwarded to the next
	as usual for an SR packet. As long as the packet travels within the		segment. Within the SR Domain no further HMAC check need be
	SR domain, no further HMAC check needs to be done. Subsequent		performed. However, other segments in the SR domain MAY verify the
	routers in the SR domain MAY verify the HMAC TLV when they process		HMAC TLV when the SRH is processed, dependent on local policy.
	the SRH (i.e. when they are the destination).
	If the validation fails, then this packet MUST be dropped, an ICMP		If HMAC validation fails an ICMP error message (parameter problem)
	error message (parameter problem) SHOULD be generated (but rate		SHOULD be generated (but rate limited) and SHOULD be logged.
	limited) and SHOULD be logged.
	6.3.3. SR path exposure		6.3.3. SR path exposure
	As the intermediate SR nodes addresses appears in the SRH, if this		The SRH contains a Segment List. If an observer outside the SR
	SRH is visible to an outsider then he/she could reuse this knowledge		Domain is able to inspect the SRH, they may use the segments in the
	to launch an attack on the intermediate SR nodes or get some insider		Segment List to launch an attack on the SR Domain or obtain knowledge
	knowledge on the topology. This is especially applicable when the		of the topology within the SR Domain. When the SR Source node is
	path between the source node and the first SR domain ingress router		outside the SR Domain and the packet traverses the public internet to
	is on the public Internet.		the SR Domain ingress router it is likely that others will have
			access to the Segment List in the SRH.
	The first remark is to state that 'security by obscurity' is never		IPSec Encapsulating Security Payload (ESP), [RFC4303], cannot be use
	enough; in other words, the security policy of the SR domain MUST		to protect the SRH as the ESP header must appear after the routing
	assume that the internal topology and addressing is known by the		header (including SRH).
	attacker. A simple traceroute will also give the same information
	(with even more information as all intermediate nodes between SID
	will also be exposed). IPsec Encapsulating Security Payload
	[RFC4303] cannot be use to protect the SRH as per RFC4303 the ESP
	header must appear after any routing header (including SRH).
	To prevent a user to leverage the gained knowledge by intercepting		Exposure of segments and TLV content to observers outside the SR
	SRH, it it recommended to apply an infrastructure Access Control List		Domain should be considered in any deployment. There are two methods
	(iACL) at the edge of the SR domain. This iACL will drop all packets		to limit exposure, and attacks on segments within the SR Domain from
	from outside the SR-domain whose destination is any address of any		outside the SR Domain:
	router interface or SID inside the domain. This security policy
	should be tuned for local operations.		Limit the number of segments and the TLV data exposed in SRH from
			nodes outside the SR Domain.
			Restrict which SIDs may accept traffic from outside the SR Domain
			to only those enforcing HMAC verification by using iACLs (as
			described in Section 6.3.2).
	6.3.4. Impact of BCP-38		6.3.4. Impact of BCP-38
	BCP-38 [RFC2827], also known as "Network Ingress Filtering", checks		BCP-38 [RFC2827], also known as "Network Ingress Filtering", checks
	whether the source address of packets received on an interface is		whether the source address of packets received on an interface is
	valid for this interface. The use of loose source routing such as		valid for this interface. The use of loose source routing such as
	SRH forces packets to follow a path which differs from the expected		SRH forces packets to follow a path which differs from the expected
	routing. Therefore, if BCP-38 was implemented in all routers inside		routing. Therefore, if BCP-38 was implemented in all routers inside
	the SR domain, then SR packets could be received by an interface		the SR domain, SR packets could be received by an interface which is
	which is not expected one and the packets could be dropped.		not the expected one, and the packets could be dropped.
	As an SR domain is usually a subset of one administrative domain, and		As BCP-38 is only deployed at the ingress routers of an
	as BCP-38 is only deployed at the ingress routers of this		administrative domain, and as Packets arriving at those ingress
	administrative domain and as packets arriving at those ingress		routers have been forwarded using the routing information, then there
	routers have been normally forwarded using the normal routing		is no reason why this ingress router should drop the SRH packet based
	information, then there is no reason why this ingress router should		on BCP-38. Routers inside the domain commonly do not apply BCP-38;
	drop the SRH packet based on BCP-38. Routers inside the domain		so, this is not a problem.
	commonly do not apply BCP-38; so, this is not a problem.
	7. IANA Considerations		7. IANA Considerations
	This document makes the following registrations in the Internet		This document makes the following registrations in the Internet
	Protocol Version 6 (IPv6) Parameters "Routing Type" registry		Protocol Version 6 (IPv6) Parameters "Routing Type" registry
	maintained by IANA:		maintained by IANA:
	Suggested Description Reference		Suggested Description Reference
	Value		Value
	----------------------------------------------------------		----------------------------------------------------------
	skipping to change at page 26, line 48 ¶		skipping to change at page 27, line 18 ¶
	[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation		[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
	of Type 0 Routing Headers in IPv6", RFC 5095,		of Type 0 Routing Headers in IPv6", RFC 5095,
	DOI 10.17487/RFC5095, December 2007,		DOI 10.17487/RFC5095, December 2007,
	<https://www.rfc-editor.org/info/rfc5095>.		<https://www.rfc-editor.org/info/rfc5095>.
	[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain		[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
	of Interpretation", RFC 6407, DOI 10.17487/RFC6407,		of Interpretation", RFC 6407, DOI 10.17487/RFC6407,
	October 2011, <https://www.rfc-editor.org/info/rfc6407>.		October 2011, <https://www.rfc-editor.org/info/rfc6407>.
			[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
			2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
			May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6		[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>.
	11.2. Informative References		11.2. Informative References
	[I-D.filsfils-spring-srv6-interop]		[I-D.filsfils-spring-srv6-interop]
	Filsfils, C., Clad, F., Camarillo, P., Abdelsalam, A.,		Filsfils, C., Clad, F., Camarillo, P., Abdelsalam, A.,
	Salsano, S., Bonaventure, O., Horn, J., and J. Liste,		Salsano, S., Bonaventure, O., Horn, J., and J. Liste,
	skipping to change at page 27, line 25 ¶		skipping to change at page 27, line 47 ¶
	daniel.bernier@bell.ca, d., Steinberg, D., Raszuk, R.,		daniel.bernier@bell.ca, d., Steinberg, D., Raszuk, R.,
	Matsushima, S., Lebrun, D., Decraene, B., Peirens, B.,		Matsushima, S., Lebrun, D., Decraene, B., Peirens, B.,
	Salsano, S., Naik, G., Elmalky, H., Jonnalagadda, P., and		Salsano, S., Naik, G., Elmalky, H., Jonnalagadda, P., and
	M. Sharif, "SRv6 Network Programming", draft-filsfils-		M. Sharif, "SRv6 Network Programming", draft-filsfils-
	spring-srv6-network-programming-04 (work in progress),		spring-srv6-network-programming-04 (work in progress),
	March 2018.		March 2018.
	[I-D.ietf-spring-segment-routing-mpls]		[I-D.ietf-spring-segment-routing-mpls]
	Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,		Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
	Litkowski, S., and R. Shakir, "Segment Routing with MPLS		Litkowski, S., and R. Shakir, "Segment Routing with MPLS
	data plane", draft-ietf-spring-segment-routing-mpls-13		data plane", draft-ietf-spring-segment-routing-mpls-14
	(work in progress), April 2018.		(work in progress), June 2018.
	[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-		[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
	Hashing for Message Authentication", RFC 2104,		Hashing for Message Authentication", RFC 2104,
	DOI 10.17487/RFC2104, February 1997,		DOI 10.17487/RFC2104, February 1997,
	<https://www.rfc-editor.org/info/rfc2104>.		<https://www.rfc-editor.org/info/rfc2104>.
	[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:		[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
	Defeating Denial of Service Attacks which employ IP Source		Defeating Denial of Service Attacks which employ IP Source
	Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,		Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
	May 2000, <https://www.rfc-editor.org/info/rfc2827>.		May 2000, <https://www.rfc-editor.org/info/rfc2827>.
	skipping to change at page 28, line 31 ¶		skipping to change at page 29, line 7 ¶
	DOI 10.17487/RFC6554, March 2012,		DOI 10.17487/RFC6554, March 2012,
	<https://www.rfc-editor.org/info/rfc6554>.		<https://www.rfc-editor.org/info/rfc6554>.
	[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for		[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
	Writing an IANA Considerations Section in RFCs", BCP 26,		Writing an IANA Considerations Section in RFCs", BCP 26,
	RFC 8126, DOI 10.17487/RFC8126, June 2017,		RFC 8126, DOI 10.17487/RFC8126, June 2017,
	<https://www.rfc-editor.org/info/rfc8126>.		<https://www.rfc-editor.org/info/rfc8126>.
	Authors' Addresses		Authors' Addresses
	Stefano Previdi
	Individual
	Italy
	Email: stefano@previdi.net
	Clarence Filsfils (editor)		Clarence Filsfils (editor)
	Cisco Systems, Inc.		Cisco Systems, Inc.
	Brussels		Brussels
	BE		BE
	Email: cfilsfil@cisco.com		Email: cfilsfil@cisco.com
			Stefano Previdi
			Individual
			Italy
			Email: stefano@previdi.net
	John Leddy		John Leddy
	Comcast		Comcast
	4100 East Dry Creek Road		4100 East Dry Creek Road
	Centennial, CO 80122		Centennial, CO 80122
	US		US
	Email: John_Leddy@comcast.com		Email: John_Leddy@comcast.com
	Satoru Matsushima		Satoru Matsushima
	Softbank		Softbank
	Email: satoru.matsushima@g.softbank.co.jp		Email: satoru.matsushima@g.softbank.co.jp
	Daniel Voyer (editor)		Daniel Voyer (editor)
	Bell Canada		Bell Canada
	Email: daniel.voyer@bell.ca		Email: daniel.voyer@bell.ca
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