draft-ietf-mpls-sr-over-ip-00.txt		draft-ietf-mpls-sr-over-ip-01.txt
	Network Working Group X. Xu		Network Working Group X. Xu
	Internet-Draft Alibaba		Internet-Draft Alibaba Inc.
	Intended status: Standards Track S. Bryant		Intended status: Standards Track S. Bryant
	Expires: February 2, 2019 Huawei		Expires: April 21, 2019 Huawei
	A. Farrel		A. Farrel
	Juniper		Old Dog Consulting
	S. Hassan		S. Hassan
	Cisco		Cisco
	W. Henderickx		W. Henderickx
	Nokia		Nokia
	Z. Li		Z. Li
	Huawei		Huawei
	August 01, 2018		October 18, 2018
	SR-MPLS over IP		SR-MPLS over IP
	draft-ietf-mpls-sr-over-ip-00		draft-ietf-mpls-sr-over-ip-01
	Abstract		Abstract
	MPLS Segment Routing (SR-MPLS in short) is an MPLS data plane-based		MPLS Segment Routing (SR-MPLS) is an MPLS data plane-based source
	source routing paradigm in which the sender of a packet is allowed to		routing paradigm in which the sender of a packet is allowed to
	partially or completely specify the route the packet takes through		partially or completely specify the route the packet takes through
	the network by imposing stacked MPLS labels on the packet. SR-MPLS		the network by imposing stacked MPLS labels on the packet. SR-MPLS
	could be leveraged to realize a source routing mechanism across MPLS,		could be leveraged to realize a source routing mechanism across MPLS,
	IPv4, and IPv6 data planes by using an MPLS label stack as a source		IPv4, and IPv6 data planes by using an MPLS label stack as a source
	routing instruction set while preserving backward compatibility with		routing instruction set while preserving backward compatibility with
	SR-MPLS.		SR-MPLS.
	This document describes how SR-MPLS capable routers and IP-only		This document describes how SR-MPLS capable routers and IP-only
	routers can seamlessly co-exist and interoperate through the use of		routers can seamlessly co-exist and interoperate through the use of
	SR-MPLS label stacks and IP encapsulation/tunneling such as MPLS-in-		SR-MPLS label stacks and IP encapsulation/tunneling such as MPLS-in-
	skipping to change at page 2, line 4 ¶		skipping to change at page 2, line 4 ¶
	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 February 2, 2019.		This Internet-Draft will expire on April 21, 2019.
	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
	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 . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3		1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	4. Procedures of SR-MPLS over IP . . . . . . . . . . . . . . . . 5		3. Procedures of SR-MPLS over IP . . . . . . . . . . . . . . . . 5
	4.1. Forwarding Entry Construction . . . . . . . . . . . . . . 5		3.1. Forwarding Entry Construction . . . . . . . . . . . . . . 5
	4.2. Packet Forwarding Procedures . . . . . . . . . . . . . . 7		3.2. Packet Forwarding Procedures . . . . . . . . . . . . . . 7
	4.2.1. Packet Forwarding with Penultimate Hop Popping . . . 8		3.2.1. Packet Forwarding with Penultimate Hop Popping . . . 8
	4.2.2. Packet Forwarding without Penultimate Hop Popping . . 9		3.2.2. Packet Forwarding without Penultimate Hop Popping . . 9
	4.2.3. Additional Forwarding Procedures . . . . . . . . . . 10		3.2.3. Additional Forwarding Procedures . . . . . . . . . . 10
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 12		5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
	7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12		6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12
	8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13		7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . 13		8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
	9.1. Normative References . . . . . . . . . . . . . . . . . . 13		8.1. Normative References . . . . . . . . . . . . . . . . . . 13
	9.2. Informative References . . . . . . . . . . . . . . . . . 15		8.2. Informative References . . . . . . . . . . . . . . . . . 14
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
	1. Introduction		1. Introduction
	MPLS Segment Routing (SR-MPLS in short)		MPLS Segment Routing (SR-MPLS) [I-D.ietf-spring-segment-routing-mpls]
	[I-D.ietf-spring-segment-routing-mpls] is an MPLS data plane-based		is an MPLS data plane-based source routing paradigm in which the
	source routing paradigm in which the sender of a packet is allowed to		sender of a packet is allowed to partially or completely specify the
	partially or completely specify the route the packet takes through		route the packet takes through the network by imposing stacked MPLS
	the network by imposing stacked MPLS labels on the packet. SR-MPLS		labels on the packet. SR-MPLS could be leveraged to realize a source
	could be leveraged to realize a source routing mechanism across MPLS,		routing mechanism across MPLS, IPv4, and IPv6 data planes by using an
	IPv4, and IPv6 data planes by using an MPLS label stack as a source		MPLS label stack as a source routing instruction set while preserving
	routing instruction set while preserving backward compatibility with		backward compatibility with SR-MPLS. More specifically, the source
	SR-MPLS. More specifically, the source routing instruction set		routing instruction set information contained in a source routed
	information contained in a source routed packet could be uniformly		packet could be uniformly encoded as an MPLS label stack no matter
	encoded as an MPLS label stack no matter whether the underlay is		whether the underlay is IPv4, IPv6, or MPLS.
	IPv4, IPv6, or MPLS.
	This document describes how SR-MPLS capable routers and IP-only		This document describes how SR-MPLS capable routers and IP-only
	routers can seamlessly co-exist and interoperate through the use of		routers can seamlessly co-exist and interoperate through the use of
	SR-MPLS label stacks and IP encapsulation/tunneling such as MPLS-in-		SR-MPLS label stacks and IP encapsulation/tunneling such as MPLS-in-
	UDP [RFC7510].		UDP [RFC7510].
	Although the source routing instructions are encoded as MPLS labels,		Section 2 describes various use cases for the tunneling SR-MPLS over
	this is a hardware convenience rather than an indication that the		IP. Section 3 describes a typical application scenario and how the
	whole MPLS protocol stack needs to be deployed. In particular, the
	MPLS control protocols are not used in this or any other form of SR-
	MPLS.
	Section 3 describes various use cases for the tunneling SR-MPLS over
	IP. Section 4 describes a typical application scenario and how the
	packet forwarding happens.		packet forwarding happens.
	2. Terminology		1.1. Terminology
	This memo makes use of the terms defined in [RFC3031] and		This memo makes use of the terms defined in [RFC3031] and
	[I-D.ietf-spring-segment-routing-mpls].		[I-D.ietf-spring-segment-routing-mpls].
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	3. Use Cases		2. Use Cases
	Tunneling SR-MPLS using IPv4 and/or IPv6 tunnels is useful at least		Tunneling SR-MPLS using IPv4 and/or IPv6 tunnels is useful at least
	in the following use cases:		in the following use cases:
	o Incremental deployment of the SR-MPLS technology may be		o Incremental deployment of the SR-MPLS technology may be
	facilitated by tunneling SR-MPLS packets across parts of a network		facilitated by tunneling SR-MPLS packets across parts of a network
	that are not SR-MPLS enabled using an IP tunneling mechanism such		that are not SR-MPLS enabled using an IP tunneling mechanism such
	as MPLS-in-UDP [RFC7510]. The tunnel destination address is the		as MPLS-in-UDP [RFC7510]. The tunnel destination address is the
	address of the next SR-MPLS-capable node along the path (i.e., the		address of the next SR-MPLS capable node along the path (i.e., the
	egress of the active node segment). This is shown in Figure 1.		egress of the active node segment). This is shown in Figure 1.
	________________________		________________________
	_______ ( ) _______		_______ ( ) _______
	( ) ( IP Network ) ( )		( ) ( IP Network ) ( )
	( SR-MPLS ) ( ) ( SR-MPLS )		( SR-MPLS ) ( ) ( SR-MPLS )
	( Network ) ( ) ( Network )		( Network ) ( ) ( Network )
	( -------- -------- )		( -------- -------- )
	( | Border | SR-in-UDP Tunnel | Border | )		( | Border | SR-in-UDP Tunnel | Border | )
	( | Router |========================| Router | )		( | Router |========================| Router | )
	skipping to change at page 4, line 26 ¶		skipping to change at page 4, line 26 ¶
	( ) ( ) ( )		( ) ( ) ( )
	(_______) ( ) (_______)		(_______) ( ) (_______)
	(________________________)		(________________________)
	Figure 1: SR-MPLS in UDP to Tunnel Between SR-MPLS Sites		Figure 1: SR-MPLS in UDP to Tunnel Between SR-MPLS Sites
	o If encoding of entropy is desired, IP tunneling mechanisms that		o If encoding of entropy is desired, IP tunneling mechanisms that
	allow encoding of entropy, such as MPLS-in-UDP encapsulation		allow encoding of entropy, such as MPLS-in-UDP encapsulation
	[RFC7510] where the source port of the UDP header is used as an		[RFC7510] where the source port of the UDP header is used as an
	entropy field, may be used to maximize the utilization of ECMP		entropy field, may be used to maximize the utilization of ECMP
	and/or UCMP, specially when it is difficult to make use of entropy		and/or LAG, especially when it is difficult to make use of entropy
	label mechanism. Refer to [I-D.ietf-mpls-spring-entropy-label])		label mechanism. Refer to [I-D.ietf-mpls-spring-entropy-label])
	for more discussion about using entropy label in SR-MPLS.		for more discussion about using entropy label in SR-MPLS.
	o Tunneling MPLS into IP provides a technology that enables SR in an		o Tunneling MPLS into IP provides a technology that enables SR in an
	IPv4 and/or IPv6 network where the routers do not support SRv6		IPv4 and/or IPv6 network where the routers do not support SRv6
	capabilities [I-D.ietf-6man-segment-routing-header] and where MPLS		capabilities [I-D.ietf-6man-segment-routing-header] and where MPLS
	forwarding is not an option. This is shown in Figure Figure 2.		forwarding is not an option. This is shown in Figure Figure 2.
	__________________________________		__________________________________
	__( IP Network )__		__( IP Network )__
	skipping to change at page 5, line 25 ¶		skipping to change at page 5, line 25 ¶
	(__ __)		(__ __)
	(__________________________________)		(__________________________________)
	Key:		Key:
	IR : IP-only Router		IR : IP-only Router
	SR : SR-MPLS-capable Router		SR : SR-MPLS-capable Router
	== : SR-MPLS in UDP Tunnel		== : SR-MPLS in UDP Tunnel
	Figure 2: SR-MPLS Enabled Within an IP Network		Figure 2: SR-MPLS Enabled Within an IP Network
	4. Procedures of SR-MPLS over IP		3. Procedures of SR-MPLS over IP
	This section describes the construction of forwarding information		This section describes the construction of forwarding information
	base (FIB) entries and the forwarding behavior that allow the		base (FIB) entries and the forwarding behavior that allow the
	deployment of SR-MPLS when some routers in the network are IP only		deployment of SR-MPLS when some routers in the network are IP only
	(i.e., do not support SR-MPLS). Note that the examples described in		(i.e., do not support SR-MPLS). Note that the examples in
	Section 4.1 and Section 4.2 assume that OSPF or ISIS is enabled: in		Section 3.1 and Section 3.2 assume that OSPF or ISIS is enabled: in
	fact, other mechanisms of discovery and advertisement could be used		fact, other mechanisms of discovery and advertisement could be used
	including other routing protocols (such as BGP) or a central		including other routing protocols (such as BGP) or a central
	controller.		controller.
	4.1. Forwarding Entry Construction		3.1. Forwarding Entry Construction
	This sub-section describes the how to construct the forwarding		This sub-section describes the how to construct the forwarding
	information base (FIB) entry on an SR-MPLS-capable router when some		information base (FIB) entry on an SR-MPLS-capable router when some
	or all of the next-hops along the shortest path towards a prefix-SID		or all of the next-hops along the shortest path towards a prefix
	are IP-only routers.		Segment Identifier （prefix-SID） are IP-only routers.
	Consider router A that receives a labeled packet with top label L(E)		Consider router A that receives a labeled packet with top label L(E)
	that corresponds to the prefix-SID SID(E) of prefix P(E) advertised		that corresponds to the prefix-SID SID(E) of prefix P(E) advertised
	by router E. Suppose the ith next-hop router (termed NHi) along the		by router E. Suppose the i-th next-hop router (termed NHi) along the
	shortest path from router A toward SID(E) is not SR-MPLS capable		shortest path from router A toward SID(E) is not SR-MPLS capable
	while both routers A and E are SR-MPLS capable. The following		while both routers A and E are SR-MPLS capable. The following
	processing steps apply:		processing steps apply:
	o Router E is SR-MPLS capable so it advertises the SR-Capabilities		o Router E is SR-MPLS capable so it advertises the SRGB as described
	sub-TLV including the SRGB as described in		in [I-D.ietf-ospf-segment-routing-extensions] and
	[I-D.ietf-ospf-segment-routing-extensions] and
	[I-D.ietf-isis-segment-routing-extensions].		[I-D.ietf-isis-segment-routing-extensions].
	o Router E advertises the prefix-SID SID(E) of prefix P(E) so MUST		o When Router E advertises the prefix-SID SID(E) of prefix P(E) it
	also advertise the encapsulation endpoint and the tunnel type of		MUST also advertise the encapsulation endpoint and the tunnel type
	any tunnel used to reach E. It does this using the mechanisms		of any tunnel used to reach E. It does this using the mechanisms
	described in [I-D.ietf-isis-encapsulation-cap] or		described in [I-D.ietf-isis-encapsulation-cap] or
	[I-D.ietf-ospf-encapsulation-cap].		[I-D.ietf-ospf-encapsulation-cap].
	o If A and E are in different IGP areas/levels, then:		o If A and E are in different IGP areas/levels, then:
	* The OSPF Tunnel Encapsulation TLV		* The OSPF Tunnel Encapsulation TLV
	[I-D.ietf-ospf-encapsulation-cap] or the ISIS Tunnel		[I-D.ietf-ospf-encapsulation-cap] or the ISIS Tunnel
	Encapsulation sub-TLV [I-D.ietf-isis-encapsulation-cap] is		Encapsulation sub-TLV [I-D.ietf-isis-encapsulation-cap] is
	flooded domain-wide.		flooded domain-wide.
	skipping to change at page 7, line 16 ¶		skipping to change at page 7, line 16 ¶
	swap the top label to a value equal to SID(E) plus the lower		swap the top label to a value equal to SID(E) plus the lower
	bound of the SRGB of E		bound of the SRGB of E
	* Encapsulate the packet according to the encapsulation		* Encapsulate the packet according to the encapsulation
	advertised in [I-D.ietf-isis-encapsulation-cap] or		advertised in [I-D.ietf-isis-encapsulation-cap] or
	[I-D.ietf-ospf-encapsulation-cap]		[I-D.ietf-ospf-encapsulation-cap]
	* Send the packet towards the next hop NHi.		* Send the packet towards the next hop NHi.
	4.2. Packet Forwarding Procedures		3.2. Packet Forwarding Procedures
	[RFC7510] specifies an IP-based encapsulation for MPLS, i.e., MPLS-		[RFC7510] specifies an IP-based encapsulation for MPLS, i.e., MPLS-
	in-UDP, which is applicable in some circumstances where IP-based		in-UDP, which is applicable in some circumstances where IP-based
	encapsulation for MPLS is required and further fine-grained load		encapsulation for MPLS is required and further fine-grained load
	balancing of MPLS packets over IP networks over Equal-Cost Multipath		balancing of MPLS packets over IP networks over Equal-Cost Multipath
	(ECMP) and/or Link Aggregation Groups (LAGs) is required as well.		(ECMP) and/or Link Aggregation Groups (LAGs) is required as well.
	This section provides details about the forwarding procedure when		This section provides details about the forwarding procedure when
	when UDP encapsulation is adopted for SR-MPLS over IP.		when UDP encapsulation is adopted for SR-MPLS over IP.
	Nodes that are SR-MPLS capable can process SR-MPLS packets. Not all		Nodes that are SR-MPLS capable can process SR-MPLS packets. Not all
	of the nodes in an SR-MPLS domain are SR-MPLS capable. Some nodes		of the nodes in an SR-MPLS domain are SR-MPLS capable. Some nodes
	may be "legacy routers" that cannot handle SR-MPLS packets but can		may be "legacy routers" that cannot handle SR-MPLS packets but can
	forward IP packets. An SR-MPLS-capable node may advertise its		forward IP packets. An SR-MPLS-capable node may advertise its
	capabilities using the IGP as described in Section 4. There are six		capabilities using the IGP as described in Section 3. There are six
	types of node in an SR-MPLS domain:		types of node in an SR-MPLS domain:
	o Domain ingress nodes that receive packets and encapsulate them for		o Domain ingress nodes that receive packets and encapsulate them for
	transmission across the domain. Those packets may be any payload		transmission across the domain. Those packets may be any payload
	protocol including native IP packets or packets that are already		protocol including native IP packets or packets that are already
	MPLS encapsulated.		MPLS encapsulated.
	o Legacy transit nodes that are IP routers but that are not SR-MPLS		o Legacy transit nodes that are IP routers but that are not SR-MPLS
	capable (i.e., are not able to perform segment routing).		capable (i.e., are not able to perform segment routing).
	skipping to change at page 8, line 5 ¶		skipping to change at page 8, line 5 ¶
	o Transit nodes that are SR-MPLS capable and need to perform SR-MPLS		o Transit nodes that are SR-MPLS capable and need to perform SR-MPLS
	routing because they are identified by a SID in the SID stack.		routing because they are identified by a SID in the SID stack.
	o The penultimate SR-MPLS capable node on the path that processes		o The penultimate SR-MPLS capable node on the path that processes
	the last SID on the stack on behalf of the domain egress node.		the last SID on the stack on behalf of the domain egress node.
	o The domain egress node that forwards the payload packet for		o The domain egress node that forwards the payload packet for
	ultimate delivery.		ultimate delivery.
	4.2.1. Packet Forwarding with Penultimate Hop Popping		3.2.1. Packet Forwarding with Penultimate Hop Popping
	The description in this section assumes that the label associated		The description in this section assumes that the label associated
	with each prefix-SID is advertised by the owner of the prefix-SID is		with each prefix-SID is advertised by the owner of the prefix-SID is
	a Penultimate Hop Popping (PHP) label. That is, the NP flag in OSPF		a Penultimate Hop Popping (PHP) label. That is, the NP flag in OSPF
	or the P flag in ISIS associated with the prefix SID is not set.		or the P flag in ISIS associated with the prefix SID is not set.
	+-----+ +-----+ +-----+ +-----+ +-----+		+-----+ +-----+ +-----+ +-----+ +-----+
	| A +-------+ B +-------+ C +--------+ D +--------+ H |		| A +-------+ B +-------+ C +--------+ D +--------+ H |
	+-----+ +--+--+ +--+--+ +--+--+ +-----+		+-----+ +--+--+ +--+--+ +--+--+ +-----+
	| | |		| | |
	skipping to change at page 9, line 37 ¶		skipping to change at page 9, line 37 ¶
	protocol. That is, the final SR-MPLS has been popped exposing the		protocol. That is, the final SR-MPLS has been popped exposing the
	payload packet.		payload packet.
	To handle this, when a router (here it is router G) pops the final		To handle this, when a router (here it is router G) pops the final
	SR-MPLS label, it inserts an explicit null label [RFC3032] before		SR-MPLS label, it inserts an explicit null label [RFC3032] before
	encapsulating the packet in an MPLS-over-UDP tunnel toward router H		encapsulating the packet in an MPLS-over-UDP tunnel toward router H
	and sending it out. That is, router G pops the top label, discovers		and sending it out. That is, router G pops the top label, discovers
	it has reached the bottom of stack, pushes an explicit null label,		it has reached the bottom of stack, pushes an explicit null label,
	and then encapsulates the MPLS packet in a UDP tunnel to router H.		and then encapsulates the MPLS packet in a UDP tunnel to router H.
	4.2.2. Packet Forwarding without Penultimate Hop Popping		3.2.2. Packet Forwarding without Penultimate Hop Popping
	Figure 4 demonstrates the packet walk in the case where the label		Figure 4 demonstrates the packet walk in the case where the label
	associated with each prefix-SID advertised by the owner of the		associated with each prefix-SID advertised by the owner of the
	prefix-SID is not a Penultimate Hop Popping (PHP) label (i.e., the		prefix-SID is not a Penultimate Hop Popping (PHP) label (i.e., the
	the NP flag in OSPF or the P flag in ISIS associated with the prefix		the NP flag in OSPF or the P flag in ISIS associated with the prefix
	SID is set). Apart from the PHP function the roles of the routers is		SID is set). Apart from the PHP function the roles of the routers is
	unchanged from Section 4.2.1.		unchanged from Section 3.2.1.
	+-----+ +-----+ +-----+ +-----+ +-----+		+-----+ +-----+ +-----+ +-----+ +-----+
	| A +-------+ B +-------+ C +--------+ D +--------+ H |		| A +-------+ B +-------+ C +--------+ D +--------+ H |
	+-----+ +--+--+ +--+--+ +--+--+ +-----+		+-----+ +--+--+ +--+--+ +--+--+ +-----+
	| | |		| | |
	| | |		| | |
	+--+--+ +--+--+ +--+--+		+--+--+ +--+--+ +--+--+
	| E +-------+ F +--------+ G |		| E +-------+ F +--------+ G |
	+-----+ +-----+ +-----+		+-----+ +-----+ +-----+
	skipping to change at page 10, line 34 ¶		skipping to change at page 10, line 34 ¶
	+--------+ +--------+ +--------+		+--------+ +--------+ +--------+
	| Packet | ---> | Packet | ---> | Packet |		| Packet | ---> | Packet | ---> | Packet |
	+--------+ +--------+ +--------+		+--------+ +--------+ +--------+
	Figure 4: Packet Forwarding Example without PHP		Figure 4: Packet Forwarding Example without PHP
	As can be seen from the figure, the SR-MPLS label for each segment is		As can be seen from the figure, the SR-MPLS label for each segment is
	left in place until the end of the segment where it is popped and the		left in place until the end of the segment where it is popped and the
	next instruction is processed.		next instruction is processed.
	4.2.3. Additional Forwarding Procedures		3.2.3. Additional Forwarding Procedures
	Non-MPLS Interfaces: Although the description in the previous two		Non-MPLS Interfaces: Although the description in the previous two
	sections is based on the use of prefix-SIDs, tunneling SR-MPLS		sections is based on the use of prefix-SIDs, tunneling SR-MPLS
	packets is useful when the top label of a received SR-MPLS packet		packets is useful when the top label of a received SR-MPLS packet
	indicates an adjacency-SID and the corresponding adjacent node to		indicates an adjacency-SID and the corresponding adjacent node to
	that adjacency-SID is not capable of MPLS forwarding but can still		that adjacency-SID is not capable of MPLS forwarding but can still
	process SR-MPLS packets. In this scenario the top label would be		process SR-MPLS packets. In this scenario the top label would be
	replaced by an IP tunnel toward that adjacent node and then		replaced by an IP tunnel toward that adjacent node and then
	forwarded over the corresponding link indicated by the adjacency-		forwarded over the corresponding link indicated by the adjacency-
	SID.		SID.
	skipping to change at page 11, line 16 ¶		skipping to change at page 11, line 16 ¶
	now an SR-MPLS-capable transit node while all the other		now an SR-MPLS-capable transit node while all the other
	assumptions keep unchanged, since F is not identified by a SID in		assumptions keep unchanged, since F is not identified by a SID in
	the stack and an MPLS-over-UDP tunnel is preferred to an MPLS LSP		the stack and an MPLS-over-UDP tunnel is preferred to an MPLS LSP
	according to local policies, router E would replace the current		according to local policies, router E would replace the current
	top label with an MPLS-over-UDP tunnel toward router G and send it		top label with an MPLS-over-UDP tunnel toward router G and send it
	out.		out.
	IP Header Fields: When encapsulating an MPLS packet in UDP, the		IP Header Fields: When encapsulating an MPLS packet in UDP, the
	resulting packet is further encapsulated in IP for transmission.		resulting packet is further encapsulated in IP for transmission.
	IPv4 or IPv6 may be used according to the capabilities of the		IPv4 or IPv6 may be used according to the capabilities of the
	network. The address fields are set as described in Section 3.		network. The address fields are set as described in Section 2.
	The other IP header fields (such as DSCP code point, or IPv6 Flow		The other IP header fields (such as DSCP code point, or IPv6 Flow
	Label) on each UDP-encapsulated segment can be set according to		Label) on each UDP-encapsulated segment can be set according to
	the operator's policy: they may be copied from the header of the		the operator's policy: they may be copied from the header of the
	incoming packet; they may be promoted from the header of the		incoming packet; they may be promoted from the header of the
	payload packet; they may be set according to instructions		payload packet; they may be set according to instructions
	programmed to be associated with the SID; or they may be		programmed to be associated with the SID; or they may be
	configured dependent on the outgoing interface and payload.		configured dependent on the outgoing interface and payload.
	Entropy and ECMP: When encapsulating an MPLS packet with an IP		Entropy and ECMP: When encapsulating an MPLS packet with an IP
	tunnel header that is capable of encoding entropy (such as		tunnel header that is capable of encoding entropy (such as
	skipping to change at page 11, line 44 ¶		skipping to change at page 11, line 44 ¶
	copied to the source port of the UDP header. Otherwise, the		copied to the source port of the UDP header. Otherwise, the
	encapsulator may have to perform a hash on the whole label stack		encapsulator may have to perform a hash on the whole label stack
	or the five-tuple of the SR-MPLS payload if the payload is		or the five-tuple of the SR-MPLS payload if the payload is
	determined as an IP packet. To avoid re-performing the hash or		determined as an IP packet. To avoid re-performing the hash or
	hunting for the entropy label each time the packet is encapsulated		hunting for the entropy label each time the packet is encapsulated
	in a UDP tunnel it MAY be desirable that the entropy value		in a UDP tunnel it MAY be desirable that the entropy value
	contained in the incoming packet (i.e., the UDP source port value)		contained in the incoming packet (i.e., the UDP source port value)
	is retained when stripping the UDP header and is re-used as the		is retained when stripping the UDP header and is re-used as the
	entropy value of the outgoing packet.		entropy value of the outgoing packet.
	5. IANA Considerations		4. IANA Considerations
	This document makes no requests for IANA action.		This document makes no requests for IANA action.
	6. Security Considerations		5. Security Considerations
	The security consideration of [RFC8354] and [RFC7510] apply. DTLS		The security consideration of [RFC8354] and [RFC7510] apply. DTLS
	[RFC6347] SHOULD be used where security is needed on an MPLS-SR-over-		[RFC6347] SHOULD be used where security is needed on an MPLS-SR-over-
	UDP segment.		UDP segment.
	It is difficult for an attacker to pass a raw MPLS encoded packet		It is difficult for an attacker to pass a raw MPLS encoded packet
	into a network and operators have considerable experience at		into a network and operators have considerable experience at
	excluding such packets at the network boundaries.		excluding such packets at the network boundaries.
	It is easy for an ingress node to detect any attempt to smuggle an IP		It is easy for an ingress node to detect any attempt to smuggle an IP
	packet into the network since it would see that the UDP destination		packet into the network since it would see that the UDP destination
	port was set to MPLS. SR packets not having a destination address		port was set to MPLS. SR packets not having a destination address
	terminating in the network would be transparently carried and would		terminating in the network would be transparently carried and would
	pose no security risk to the network under consideration.		pose no security risk to the network under consideration.
	Where control plane techniques are used (as described in		Where control plane techniques are used (as described in
	Authors' Addresses it is important that these protocols are		Authors' Addresses it is important that these protocols are
	adequately secured for the environment in which they are run.		adequately secured for the environment in which they are run.
	7. Contributors		6. Contributors
	Ahmed Bashandy		Ahmed Bashandy
	Individual		Individual
	Email: abashandy.ietf@gmail.com		Email: abashandy.ietf@gmail.com
	Clarence Filsfils		Clarence Filsfils
	Cisco		Cisco
	Email: cfilsfil@cisco.com		Email: cfilsfil@cisco.com
	John Drake		John Drake
	skipping to change at page 13, line 30 ¶		skipping to change at page 13, line 30 ¶
	Email: gunter.van_de_velde@nokia.com		Email: gunter.van_de_velde@nokia.com
	Tal Mizrahi		Tal Mizrahi
	Marvell		Marvell
	Email: talmi@marvell.com		Email: talmi@marvell.com
	Jeff Tantsura		Jeff Tantsura
	Individual		Individual
	Email: jefftant@gmail.com		Email: jefftant@gmail.com
	8. Acknowledgements		7. Acknowledgements
	Thanks to Joel Halpern, Bruno Decraene, Loa Andersson, Ron Bonica,		Thanks to Joel Halpern, Bruno Decraene, Loa Andersson, Ron Bonica,
	Eric Rosen, Jim Guichard, and Gunter Van De Velde for their		Eric Rosen, Jim Guichard, and Gunter Van De Velde for their
	insightful comments on this draft.		insightful comments on this draft.
	9. References		8. References
	9.1. Normative References
	[I-D.ietf-isis-encapsulation-cap]
	Xu, X., Decraene, B., Raszuk, R., Chunduri, U., Contreras,
	L., and L. Jalil, "Advertising Tunnelling Capability in
	IS-IS", draft-ietf-isis-encapsulation-cap-01 (work in
	progress), April 2017.
	[I-D.ietf-isis-segment-routing-extensions]
	Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
	Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura,
	"IS-IS Extensions for Segment Routing", draft-ietf-isis-
	segment-routing-extensions-19 (work in progress), July
	2018.
	[I-D.ietf-ospf-encapsulation-cap]
	Xu, X., Decraene, B., Raszuk, R., Contreras, L., and L.
	Jalil, "The Tunnel Encapsulations OSPF Router
	Information", draft-ietf-ospf-encapsulation-cap-09 (work
	in progress), October 2017.
	[I-D.ietf-ospf-segment-routing-extensions]		8.1. Normative References
	Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
	Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
	Extensions for Segment Routing", draft-ietf-ospf-segment-
	routing-extensions-25 (work in progress), April 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-14		data plane", draft-ietf-spring-segment-routing-mpls-14
	(work in progress), June 2018.		(work in progress), June 2018.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	skipping to change at page 15, line 24 ¶		skipping to change at page 14, line 43 ¶
	[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions		[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
	for Advertising Router Information", RFC 7981,		for Advertising Router Information", RFC 7981,
	DOI 10.17487/RFC7981, October 2016,		DOI 10.17487/RFC7981, October 2016,
	<https://www.rfc-editor.org/info/rfc7981>.		<https://www.rfc-editor.org/info/rfc7981>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	9.2. Informative References		8.2. Informative References
	[I-D.ietf-6man-segment-routing-header]		[I-D.ietf-6man-segment-routing-header]
	Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and		Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and
	d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header		d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
	(SRH)", draft-ietf-6man-segment-routing-header-14 (work in		(SRH)", draft-ietf-6man-segment-routing-header-14 (work in
	progress), June 2018.		progress), June 2018.
	[I-D.ietf-mpls-spring-entropy-label]		[I-D.ietf-mpls-spring-entropy-label]
	Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,		Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
	Shakir, R., and J. Tantsura, "Entropy label for SPRING		Shakir, R., and J. Tantsura, "Entropy label for SPRING
	skipping to change at page 15, line 47 ¶		skipping to change at page 15, line 20 ¶
	[RFC8354] Brzozowski, J., Leddy, J., Filsfils, C., Maglione, R.,		[RFC8354] Brzozowski, J., Leddy, J., Filsfils, C., Maglione, R.,
	Ed., and M. Townsley, "Use Cases for IPv6 Source Packet		Ed., and M. Townsley, "Use Cases for IPv6 Source Packet
	Routing in Networking (SPRING)", RFC 8354,		Routing in Networking (SPRING)", RFC 8354,
	DOI 10.17487/RFC8354, March 2018,		DOI 10.17487/RFC8354, March 2018,
	<https://www.rfc-editor.org/info/rfc8354>.		<https://www.rfc-editor.org/info/rfc8354>.
	Authors' Addresses		Authors' Addresses
	Xiaohu Xu		Xiaohu Xu
	Alibaba		Alibaba Inc.
	Email: xiaohu.xxh@alibaba-inc.com		Email: xiaohu.xxh@alibaba-inc.com
	Stewart Bryant		Stewart Bryant
	Huawei		Huawei
	Email: stewart.bryant@gmail.com		Email: stewart.bryant@gmail.com
	Adrian Farrel		Adrian Farrel
	Juniper		Old Dog Consulting
	Email: afarrel@juniper.net		Email: adrian@olddog.co.uk
	Syed Hassan		Syed Hassan
	Cisco		Cisco
	Email: shassan@cisco.com		Email: shassan@cisco.com
	Wim Henderickx		Wim Henderickx
	Nokia		Nokia
	Email: wim.henderickx@nokia.com		Email: wim.henderickx@nokia.com
End of changes. 39 change blocks.
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