draft-kini-mpls-spring-entropy-label-02.txt		draft-kini-mpls-spring-entropy-label-03.txt
	Network Working Group S. Kini, Ed.		Network Working Group S. Kini, Ed.
	Internet-Draft Ericsson		Internet-Draft Ericsson
	Intended status: Informational K. Kompella		Intended status: Informational K. Kompella
	Expires: April 28, 2015 Juniper		Expires: September 4, 2015 Juniper
	S. Sivabalan		S. Sivabalan
	Cisco		Cisco
	S. Litkowski		S. Litkowski
	Orange		Orange
	R. Shakir		R. Shakir
	B.T.		B.T.
	X. Xu		X. Xu
	Huawei		Huawei
	W. Hendrickx		W. Hendrickx
	Alcatel-Lucent		Alcatel-Lucent
	J. Tantsura		J. Tantsura
	Ericsson		Ericsson
	October 25, 2014		March 3, 2015
	Entropy labels for source routed stacked tunnels		Entropy labels for source routed stacked tunnels
	draft-kini-mpls-spring-entropy-label-02		draft-kini-mpls-spring-entropy-label-03
	Abstract		Abstract
	Source routed tunnel stacking is a technique that can be leveraged to		Source routed tunnel stacking is a technique that can be leveraged to
	provide a method to steer a packet through a controlled set of		provide a method to steer a packet through a controlled set of
	segments. This can be applied to the Multi Protocol Label Switching		segments. This can be applied to the Multi Protocol Label Switching
	(MPLS) data plane. Entropy label (EL) is a technique used in MPLS to		(MPLS) data plane. Entropy label (EL) is a technique used in MPLS to
	improve load balancing. This document examines and describes how ELs		improve load balancing. This document examines and describes how ELs
	are to be applied to source routed stacked tunnels.		are to be applied to source routed stacked tunnels.
	skipping to change at page 1, line 48		skipping to change at page 1, line 48
	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 http://datatracker.ietf.org/drafts/current/.		Drafts is at http://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 April 28, 2015.		This Internet-Draft will expire on September 4, 2015.
	Copyright Notice		Copyright Notice
	Copyright (c) 2014 IETF Trust and the persons identified as the		Copyright (c) 2015 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
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	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
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	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3		1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
	2. Abbreviations and Terminology . . . . . . . . . . . . . . . . 3		2. Abbreviations and Terminology . . . . . . . . . . . . . . . . 3
	3. Use-case for multipath load balancing in source stacked		3. Use-case requiring multipath load balancing in source stacked
	tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . 4		tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
	4. Recommended EL solution for SPRING . . . . . . . . . . . . . 5		4. Recommended EL solution for SPRING . . . . . . . . . . . . . 5
	5. Options considered . . . . . . . . . . . . . . . . . . . . . 6		5. Options considered . . . . . . . . . . . . . . . . . . . . . 6
	5.1. Single EL at the bottom of the stack of tunnels . . . . . 6		5.1. Single EL at the bottom of the stack of tunnels . . . . . 6
	5.2. An EL per tunnel in the stack . . . . . . . . . . . . . . 7		5.2. An EL per tunnel in the stack . . . . . . . . . . . . . . 7
	5.3. A re-usable EL for a stack of tunnels . . . . . . . . . . 8		5.3. A re-usable EL for a stack of tunnels . . . . . . . . . . 7
	5.3.1. EL at top of stack . . . . . . . . . . . . . . . . . 8		5.3.1. EL at top of stack . . . . . . . . . . . . . . . . . 8
	5.4. ELs at readable label stack depths . . . . . . . . . . . 8		5.4. ELs at readable label stack depths . . . . . . . . . . . 8
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9		6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 9		8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
	9.1. Normative References . . . . . . . . . . . . . . . . . . 9		9.1. Normative References . . . . . . . . . . . . . . . . . . 9
	9.2. Informative References . . . . . . . . . . . . . . . . . 10		9.2. Informative References . . . . . . . . . . . . . . . . . 10
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
	skipping to change at page 4, line 6		skipping to change at page 4, line 6
	ECMP - Equal Cost Multi Paths		ECMP - Equal Cost Multi Paths
	MPLS - Multiprotocol Label Switching		MPLS - Multiprotocol Label Switching
	SID - Segment Identifier		SID - Segment Identifier
	RLD - Readable Label Depth		RLD - Readable Label Depth
	OAM - Operation, Administration and Maintenance		OAM - Operation, Administration and Maintenance
	3. Use-case for multipath load balancing in source stacked tunnels		3. Use-case requiring multipath load balancing in source stacked
			tunnels
	Source stacked tunnels have several use-cases, one of which is		+------+
	service chaining [I-D.filsfils-spring-segment-routing-use-cases].		| |
	Consider the service-chaining network in Figure 1 that has MPLS as		+-------| P3 |-----+
	the data plane. The requirement of the use-case is to create a LSP		| +-----| |---+ |
	from source LSR S, apply the services S1, S2 and finally terminate		L3| |L4 +------+ L1| |L2 +----+
	the LSP at destination LSR D. Local load balancing is required		| | | | +--| P4 |--+
	across the parallel links between P1 and S1. Local load balancing is		+-----+ +-----+ +-----+ | +----+ | +-----+
	also required between the ECMP paths from S1 to S2 i.e., between the		| S |-----| P1 |------------| P2 |--+ +--| D |
	paths S1-P1-P2-P3-S2 and S1-P1-P2-P4-S2. Segment routing can be used		| | | | | |--+ +--| |
	to achieve this. A segment to S1 is stacked above the segment to S2		+-----+ +-----+ +-----+ | +----+ | +-----+
	which in turn is stacked above the segment to D. Labels for service		+--| P5 |--+
	instructions are also inserted in the stack at appropriate depths so		+----+
	that services S1 and S2 are executed. To achieve local load
	balancing the SIDs of specific interfaces is not specified. Since
	entropy label is a standardized [RFC6790] mechanism defined for MPLS
	it can be adapted to the case of source stacked tunnels. Multiple
	ways to apply entropy labels exist and a recommended solution is
	described in Section 4 and all the options considered are listed in
	Section 5 along with their tradeoffs. We denote SN to be the node
	SID of LSR N and SN{L1,L2,...} to denote the SID of the adjacency for
	the set for links {L1,L2,...} of LSR N and S-SvcN to denote the SID
	for a service at service LSR N. The label stack that the source LSR
	S uses for the LSP can be <SS1, S-SvcS1, SS2, S-SvcS2, SD> or <SP1,
	SP1{L1,L2}, S-SvcS1, SS2, S-SvcS2, SD>.
	+-----+ +-----+		S=Source LSR, D=Destination LSR, P1,P2,P3,P4,P5=Transit LSRs,
	| S1 | +------| P3 |------+		L1,L2,L3,L4=Links
	+-----+ | +-----+ |
	L1| |L2 | |
	+-----+ +-----+ +-----+ +-----+
	| S |-----| P1 |-----| P2 | | S2 |
	+-----+ +-----+ +-----+ +-----+
	| |
	| +-----+ |
	+------| P4 |------+
	+-----+
	|
	+-----+
	| D |
	+-----+
	S=Source LSR, D=Destination LSR, S1,S2=service-LSRs, L1,L2=links,		Figure 1: Traffic engineering use-case
	P1,P2,P3,P4=Transit LSRs
	Figure 1: Service chaining use-case		Traffic-engineering (TE) is one of the applications of MPLS and is
			also a requirement for source stacked tunnels. Consider the topology
			shown in Figure 1. Lets say the LSR P1 has a limitation that it can
			only look four labels deep in the stack to do multipath decisions.
			All other transit LSRs in the figure can read deep label stacks and
			the LSR S can insert as many <ELI, EL> pairs as needed. The LSR S
			requires data to be sent to LSR D along a traffic-engineered path
			that goes over the link L1. Good load balancing is also required
			across equal cost paths (including parallel links). To engineer
			traffic along a path that takes link L1, the label stack that LSR S
			creates consists of a label to the node SID of LSR P3, stacked over
			the label for the adjacency SID of link L1 and that in turn is
			stacked over the label to the node SID of LSR D. For simplicity lets
			assume that all LSRs use the same label space for source stacked
			tunnels. Lets L_N-P denote the label to be used to reach the node
			SID of LSR P. Let L_A-Ln denote the label used for the adjacency SID
			for link Ln. The LSR S must use the label stack <L_N-P3, L_A-L1,
			L_N-D> for traffic-engineering. However to achieve good load
			balancing over the equal cost paths P2-P4-D, P2-P5-D and the parallel
			links L3, L4, a mechanism such as Entropy labels [RFC6790] should be
			adapted for source stacked tunnels. Multiple ways to apply entropy
			labels were considered and are documented in Section 5 along with
			their tradeoffs. A recommended solution is described in Section 4.
	4. Recommended EL solution for SPRING		4. Recommended EL solution for SPRING
	The solution described in this section follows [RFC6790].		The solution described in this section follows [RFC6790].
	An LSR may have a limitation in its ability to read and process the		An LSR may have a limitation in its ability to read and process the
	label stack in order to do multipath load balancing. This limitation		label stack in order to do multipath load balancing. This limitation
	expressed in terms of the number of label stack entries that the LSR		expressed in terms of the number of label stack entries that the LSR
	can read is henceforth referred to as the Readable Label Depth (RLD)		can read is henceforth referred to as the Readable Label Depth (RLD)
	capability of that LSR. If an EL does not occur within the RLD of an		capability of that LSR. If an EL does not occur within the RLD of an
	LSR in the label stack of the MPLS packet that it receives, then it		LSR in the label stack of the MPLS packet that it receives, then it
	would lead to poor load balancing at that LSR. The RLD of an LSR is		would lead to poor load balancing at that LSR. The RLD of an LSR is
	a characteristic of the forwarding plane of that LSR's implementation		a characteristic of the forwarding plane of that LSR's implementation
	and determining it is outside the scope of this document.		and determining it is outside the scope of this document.
	In order for the EL to occur within the RLD of LSRs along the path		In order for the EL to occur within the RLD of LSRs along the path
	corresponding to a label stack, multiple <ELI, EL> pairs MAY be		corresponding to a label stack, multiple <ELI, EL> pairs MAY be
	inserted in the label stack as long as the labels below which they		inserted in the label stack as long as the tunnel's label below which
	are inserted are entropy label capable. The LSR that inserts <ELI,		they are inserted are advertised with entropy label capability
	EL> pairs MAY have limitations on the number of such pairs that it		enabled. The LSR that inserts <ELI, EL> pairs MAY have limitations
	can insert and also the depth at which it can insert them. If due to		on the number of such pairs that it can insert and also the depth at
	any limitation, the inserted ELs are at positions such that an LSR		which it can insert them. If due to any limitation, the inserted ELs
	along the path receives an MPLS packet without an EL in the label		are at positions such that an LSR along the path receives an MPLS
	stack within that LSR's RLD, then the load balancing performed by		packet without an EL in the label stack within that LSR's RLD, then
	that LSR would be poor. Special attention should be paid when a		the load balancing performed by that LSR would be poor. Special
	forwarding adjacency LSP (FA-LSP) [RFC4206] is used as a link along		attention should be paid when a forwarding adjacency LSP (FA-LSP)
	the path of a source stacked LSP, since the labels of the FA-LSP		[RFC4206] is used as a link along the path of a source stacked LSP,
	would additionally count towards the depth of the label stack when		since the labels of the FA-LSP would additionally count towards the
	calculating the appropriate positions to insert the ELs. The		depth of the label stack when calculating the appropriate positions
	recommendations for inserting <ELI, EL> pairs are:		to insert the ELs. The recommendations for inserting <ELI, EL> pairs
			are:
	o An LSR that is limited in the number of <ELI, EL> pairs that it		o An LSR that is limited in the number of <ELI, EL> pairs that it
	can insert SHOULD insert such pairs deeper in the stack.		can insert SHOULD insert such pairs deeper in the stack.
	o An LSR SHOULD try to insert an <ELI, EL> pair within the RLD of		o An LSR SHOULD try to insert <ELI, EL> pairs at positions so that
	the maximum number of LSRs along the path as it can.		for the maximum number of transit LSRs, the EL occurs within the
			RLD of the incoming packet to that LSR.
	o An LSR SHOULD try to insert the minimum number of such pairs while		o An LSR SHOULD try to insert the minimum number of such pairs while
	trying to satisfy the above criteria.		trying to satisfy the above criteria.
	A sample algorithm to insert ELs is shown below. Implementations can		A sample algorithm to insert ELs is shown below. Implementations can
	choose any algorithm as long as it follows the above recommendations.		choose any algorithm as long as it follows the above recommendations.
	Initialize the current EL insertion point to the		Initialize the current EL insertion point to the
	bottommost label in the stack that is EL-capable		bottommost label in the stack that is EL-capable
	while local-node can push more labels OR		while (local-node can push more <ELI,EL> pairs OR
	top of stack has been reached {		insertion point is not above label stack) {
	insert an ELI+EL at current insertion point		insert an <ELI,EL> pair below current insertion point
	move insertion point up until current EL is out of RLD		move new insertion point up from current insertion point until
	AND		((last inserted EL is below the RLD) AND (RLD > 2)
	insertion point is EL-capable		AND
			(new insertion point is EL-capable))
	set current insertion point to new insertion point		set current insertion point to new insertion point
	}		}
	Figure 2: Algorithm to insert <ELI, EL> pairs in a label stack		Figure 2: Algorithm to insert <ELI, EL> pairs in a label stack
			When this algorithm is applied to the example described in Section 3
			it will result in ELs being inserted in two positions, one below the
			label L_N-D and another below L_N-P3. Thus the resulting label stack
			would be <L_N-P3, ELI, EL, L_A-L1, L_N-D, ELI, EL>
	The RLD can be advertised via protocols and those extensions would be		The RLD can be advertised via protocols and those extensions would be
	described in a separate document.		described in separate documents [I-D.xu-isis-mpls-elc] and
			[I-D.xu-ospf-mpls-elc].
	The recommendations above are not expected to bring any additional		The recommendations above are not expected to bring any additional
	OAM considerations beyond those described in section 6 of [RFC6790].		OAM considerations beyond those described in section 6 of [RFC6790].
	However, the OAM requirements and solutions for source stacked		However, the OAM requirements and solutions for source stacked
	tunnels are still under discussion and future revisions of this		tunnels are still under discussion and future revisions of this
	document will address those if needed.		document will address those if needed.
	5. Options considered		5. Options considered
	5.1. Single EL at the bottom of the stack of tunnels		5.1. Single EL at the bottom of the stack of tunnels
	In this option a single EL is used for the entire label stack. The		In this option a single EL is used for the entire label stack. The
	source LSR S encodes the entropy label (EL) below the labels of all		source LSR S encodes the entropy label (EL) below the labels of all
	the stacked tunnels. In Figure 1 label stack at LSR S would look		the stacked tunnels. In the example described in Section 3 it will
	like <SP1, SS1, S-SvcS1, SS2, S-SvcS2, SD, ELI, EL> <remaining packet		result in the label stack at LSR S to look like <L_N-P3, L_A-L1, L_N-
	header>. Note that the notation in [RFC6790] is used to describe the		D, ELI, EL> <remaining packet header>. Note that the notation in
	label stack. An issue with this approach is that as the label stack		[RFC6790] is used to describe the label stack. An issue with this
	grows due an increase in the number of SIDs, the EL correspondingly		approach is that as the label stack grows due an increase in the
	goes deeper in the label stack. As a result, intermediate LSRs (such		number of SIDs, the EL goes correspondingly deeper in the label
	as P1) that have to walk the label stack at least until the EL (if		stack. Hence transit LSRs have to access a larger number of bytes in
	found) to perform load balancing decisions have to access a larger		the packet header when making forwarding decisions. In the example
	number of bytes in the packet header when making forwarding		described in Section 3 the LSR P1 would poorly load-balance traffic
	decisions. A load balanced network design using this approach must		on the parallel links L3, L4 since the EL is below the RLD of the
	ensure that all intermediate LSRs have the capability to traverse the		packet received by P1. A load balanced network design using this
	maximum label stack depth in order to do effective load balancing.		approach must ensure that all intermediate LSRs have the capability
	The use-case for which the tunnel stacking is applied would determine		to traverse the maximum label stack depth as required for that
	the maximum label stack depth.		application that uses source routed stacking.
	In the case where the hardware is capable of pushing a single <ELI,		In the case where the hardware is capable of pushing a single <ELI,
	EL> pair at any depth, this option is the same as the recommended		EL> pair at any depth, this option is the same as the recommended
	solution in Section 4.		solution in Section 4.
	This option was discounted since there exist a number of hardware		This option was discounted since there exist a number of hardware
	implementations which have a low maximum readable label depth.		implementations which have a low maximum readable label depth.
	Choosing this option can lead to a loss of load-balancing using EL in		Choosing this option can lead to a loss of load-balancing using EL in
	a significant part of the network but that is a critical requirement		a significant part of the network but that is a critical requirement
	in a service provider network.		in a service provider network.
	5.2. An EL per tunnel in the stack		5.2. An EL per tunnel in the stack
	In this option each tunnel in the stack can be given its own EL. The		In this option each tunnel in the stack can be given its own EL. The
	source LSR pushes an <ELI, EL> before pushing a tunnel label when		source LSR pushes an <ELI, EL> before pushing a tunnel label when
	load balancing is required to direct traffic on that tunnel. For the		load balancing is required to direct traffic on that tunnel. In the
	same Figure 1 above, the source LSR S encoded label stack would be		example described in Section 3, the source LSR S encoded label stack
	<SS1, ELI, EL1, S-SvcS1, SS2, ELI, EL2, S-SvcS2, SD> where all the		would be <L_N-P3, ELI, EL, L_A-L1, L_N-D, ELI, EL> where all the ELs
	ELs can have the same value. Accessing the EL at an intermediate LSR		can be the same. Accessing the EL at an intermediate LSR is
	is independent of the depth of the label stack and hence independent		independent of the depth of the label stack and hence independent of
	of the specific use-case to which the stacked tunnels are applied. A		the specific application that uses source stacking on that network.
	drawback is that the depth of the label stack grows significantly,		A drawback is that the depth of the label stack grows significantly,
	almost 3 times as the number of labels in the label stack. The		almost 3 times as the number of labels in the label stack. The
	network design should ensure that source LSRs should have the		network design should ensure that source LSRs should have the
	capability to push such a deep label stack. Also, the bandwidth		capability to push such a deep label stack. Also, the bandwidth
	overhead and potential MTU issues of deep label stacks should be		overhead and potential MTU issues of deep label stacks should be
	accounted for in the network design.		accounted for in the network design.
	In the case where the RLD is the minimum value (3) for all LSRs, all		In the case where the RLD is the minimum value (3) for all LSRs, all
	LSRs are EL capable and the LSR that is inserting <ELI, EL> pairs has		LSRs are EL capable and the LSR that is inserting <ELI, EL> pairs has
	no limit on how many it can insert then this option is the same as		no limit on how many it can insert then this option is the same as
	the recommended solution in Section 4.		the recommended solution in Section 4.
	skipping to change at page 8, line 20		skipping to change at page 8, line 11
	terminated tunnel for the next inner tunnel. It does this by storing		terminated tunnel for the next inner tunnel. It does this by storing
	the EL from the outer tunnel when that tunnel is terminated and re-		the EL from the outer tunnel when that tunnel is terminated and re-
	inserting it below the next inner tunnel label during the label swap		inserting it below the next inner tunnel label during the label swap
	operation. The LSR that stacks tunnels SHOULD insert an EL below the		operation. The LSR that stacks tunnels SHOULD insert an EL below the
	outermost tunnel. It SHOULD NOT insert ELs for any inner tunnels.		outermost tunnel. It SHOULD NOT insert ELs for any inner tunnels.
	Also, the penultimate hop LSR of a segment MUST NOT pop the ELI and		Also, the penultimate hop LSR of a segment MUST NOT pop the ELI and
	EL even though they are exposed as the top labels since the		EL even though they are exposed as the top labels since the
	terminating LSR of that segment would re-use the EL for the next		terminating LSR of that segment would re-use the EL for the next
	segment.		segment.
	For the same Figure 1 above, the source LSR S encoded label stack		In Section 3 above, the source LSR S encoded label stack would be
	would be <SS11, ELI, EL, S-SvcS1, SS2, S-SvcS2, SD>. At P1 the		<L_N-P3, ELI, EL, L_A-L1, L_N-D>. At P1 the outgoing label stack
	outgoing label stack would be <SS1, ELI, EL, S-SvcS1, SS2, S-SvcS2,		would be <L_N-P3, ELI, EL, L_A-L1, L_N-D> after it has load balanced
	SD> after it has load balanced to one of the links L1 or L2. At S1		to one of the links L3 or L4. At P3 the outgoing label stack would
	the outgoing label stack would be <SS2, S-SvS2, ELI, EL, SD>. At P2		be <L_N-D, ELI, EL>. At P2 the outgoing label stack would be <L_N-D,
	the outgoing label stack would be <SS2, ELI, EL, S-SvcS2, SD> and it		ELI, EL> and it would load balance to one of the nexthop LSRs P4 or
	would load balance to one of the nexthop LSRs P3 or P4. Accessing		P5. Accessing the EL at an intermediate LSR (e.g. P1) is
	the EL at an intermediate LSR (e.g. P3) is independent of the depth		independent of the depth of the label stack and hence independent of
	of the label stack and hence independent of the specific use-case to		the specific use-case to which the stacked tunnels are applied.
	which the stacked tunnels are applied.
	This option was discounted due to the significant change in label		This option was discounted due to the significant change in label
	swap operations that would be required for existing hardware.		swap operations that would be required for existing hardware.
	5.3.1. EL at top of stack		5.3.1. EL at top of stack
	A slight variant of the re-usable EL option is to keep the EL at the		A slight variant of the re-usable EL option is to keep the EL at the
	top of the stack rather than below the tunnel label. In this case		top of the stack rather than below the tunnel label. In this case
	each LSR that is not terminating a segment should continue to keep		each LSR that is not terminating a segment should continue to keep
	the received EL at the top of the stack when forwarding the packet		the received EL at the top of the stack when forwarding the packet
	skipping to change at page 9, line 10		skipping to change at page 8, line 48
	In this option the source LSR inserts ELs for tunnels in the label		In this option the source LSR inserts ELs for tunnels in the label
	stack at depths such that each LSR along the path that must load		stack at depths such that each LSR along the path that must load
	balance is able to access at least one EL. Note that the source LSR		balance is able to access at least one EL. Note that the source LSR
	may have to insert multiple ELs in the label stack at different		may have to insert multiple ELs in the label stack at different
	depths for this to work since intermediate LSRs may have differing		depths for this to work since intermediate LSRs may have differing
	capabilities in accessing the depth of a label stack. The label		capabilities in accessing the depth of a label stack. The label
	stack depth access value of intermediate LSRs must be known to create		stack depth access value of intermediate LSRs must be known to create
	such a label stack. How this value is determined is outside the		such a label stack. How this value is determined is outside the
	scope of this document. This value can be advertised using a		scope of this document. This value can be advertised using a
	protocol such as an IGP. For the same Figure 1 above, if LSR P1		protocol such as an IGP. For the same Section 3 above, if LSR P1
	needs to have the EL within a depth of 4, then the source LSR S		needs to have the EL within a depth of 4, then the source LSR S
	encoded label stack would be <SS1, S-SvcS1, ELI, EL2, SS2, SD> where		encoded label stack would be <L_N-P3, ELI, EL, L_A-L1, L_N-D, ELI,
	all the ELs would typically have the same value.		EL> where all the ELs would typically have the same value.
	In the case where the RLD has different values along the path and the		In the case where the RLD has different values along the path and the
	LSR that is inserting <ELI, EL> pairs has no limit on how many pairs		LSR that is inserting <ELI, EL> pairs has no limit on how many pairs
	it can insert, and it knows the appropriate positions in the stack		it can insert, and it knows the appropriate positions in the stack
	where they should be inserted, then this option is the same as the		where they should be inserted, then this option is the same as the
	recommended solution in Section 4.		recommended solution in Section 4.
	A variant of this solution was selected which balances the number of		A variant of this solution was selected which balances the number of
	labels that need to be pushed against the requirement for entropy.		labels that need to be pushed against the requirement for entropy.
	6. Acknowledgements		6. Acknowledgements
	The authors would like to thank John Drake and Loa Andersson for		The authors would like to thank John Drake, Loa Andersson, Curtis
	their comments.		Villamizar, Greg Mirsky, Markus Jork, Kamran Raza and Nobo Akiya for
			their review comments and suggestions.
	7. IANA Considerations		7. IANA Considerations
	This memo includes no request to IANA.		This memo includes no request to IANA.
	8. Security Considerations		8. Security Considerations
	This document does not introduce any new security considerations		This document does not introduce any new security considerations
	beyond those already listed in [RFC6790].		beyond those already listed in [RFC6790].
	skipping to change at page 10, line 5		skipping to change at page 9, line 40
	9.1. Normative References		9.1. Normative References
	[I-D.filsfils-spring-segment-routing]		[I-D.filsfils-spring-segment-routing]
	Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,		Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
	Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,		Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
	Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,		Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
	"Segment Routing Architecture", draft-filsfils-spring-		"Segment Routing Architecture", draft-filsfils-spring-
	segment-routing-04 (work in progress), July 2014.		segment-routing-04 (work in progress), July 2014.
	[I-D.filsfils-spring-segment-routing-use-cases]
	Filsfils, C., Francois, P., Previdi, S., Decraene, B.,
	Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
	Ytti, S., Henderickx, W., Tantsura, J., Kini, S., and E.
	Crabbe, "Segment Routing Use Cases", draft-filsfils-
	spring-segment-routing-use-cases-01 (work in progress),
	October 2014.
	[I-D.gredler-spring-mpls]		[I-D.gredler-spring-mpls]
	Gredler, H., Rekhter, Y., Jalil, L., Kini, S., and X. Xu,		Gredler, H., Rekhter, Y., Jalil, L., Kini, S., and X. Xu,
	"Supporting Source/Explicitly Routed Tunnels via Stacked		"Supporting Source/Explicitly Routed Tunnels via Stacked
	LSPs", draft-gredler-spring-mpls-06 (work in progress),		LSPs", draft-gredler-spring-mpls-06 (work in progress),
	May 2014.		May 2014.
	[I-D.ravisingh-mpls-el-for-seamless-mpls]		[I-D.ravisingh-mpls-el-for-seamless-mpls]
	Singh, R., Shen, Y., and J. Drake, "Entropy label for		Singh, R., Shen, Y., and J. Drake, "Entropy label for
	seamless MPLS", draft-ravisingh-mpls-el-for-seamless-		seamless MPLS", draft-ravisingh-mpls-el-for-seamless-
	mpls-02 (work in progress), July 2014.		mpls-04 (work in progress), October 2014.
			[I-D.xu-isis-mpls-elc]
			Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
			Litkowski, "Signaling Entropy Label Capability Using IS-
			IS", draft-xu-isis-mpls-elc-01 (work in progress),
			September 2014.
			[I-D.xu-ospf-mpls-elc]
			Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
			Litkowski, "Signaling Entropy Label Capability Using
			OSPF", draft-xu-ospf-mpls-elc-01 (work in progress),
			October 2014.
	[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, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)		[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
	Hierarchy with Generalized Multi-Protocol Label Switching		Hierarchy with Generalized Multi-Protocol Label Switching
	(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.		(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
	[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and		[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
	L. Yong, "The Use of Entropy Labels in MPLS Forwarding",		L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
	RFC 6790, November 2012.		RFC 6790, November 2012.
	[RFC7325] Villamizar, C., Kompella, K., Amante, S., Malis, A., and
	C. Pignataro, "MPLS Forwarding Compliance and Performance
	Requirements", RFC 7325, August 2014.
	9.2. Informative References		9.2. Informative References
	[I-D.previdi-isis-segment-routing-extensions]		[I-D.filsfils-spring-segment-routing-use-cases]
			Filsfils, C., Francois, P., Previdi, S., Decraene, B.,
			Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
			Ytti, S., Henderickx, W., Tantsura, J., Kini, S., and E.
			Crabbe, "Segment Routing Use Cases", draft-filsfils-
			spring-segment-routing-use-cases-01 (work in progress),
			October 2014.
			[I-D.ietf-isis-segment-routing-extensions]
	Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,		Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
	Litkowski, S., and J. Tantsura, "IS-IS Extensions for		Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS
	Segment Routing", draft-previdi-isis-segment-routing-		Extensions for Segment Routing", draft-ietf-isis-segment-
	extensions-05 (work in progress), February 2014.		routing-extensions-03 (work in progress), October 2014.
	[I-D.psenak-ospf-segment-routing-extensions]		[I-D.ietf-ospf-segment-routing-extensions]
	Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,		Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
	Shakir, R., Henderickx, W., and J. Tantsura, "OSPF		Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
	Extensions for Segment Routing", draft-psenak-ospf-		Extensions for Segment Routing", draft-ietf-ospf-segment-
	segment-routing-extensions-05 (work in progress), June		routing-extensions-04 (work in progress), February 2015.
	2014.
			[RFC7325] Villamizar, C., Kompella, K., Amante, S., Malis, A., and
			C. Pignataro, "MPLS Forwarding Compliance and Performance
			Requirements", RFC 7325, August 2014.
	Authors' Addresses		Authors' Addresses
	Sriganesh Kini (editor)		Sriganesh Kini (editor)
	Ericsson		Ericsson
	Email: sriganesh.kini@ericsson.com		Email: sriganesh.kini@ericsson.com
	Kireeti Kompella		Kireeti Kompella
	Juniper		Juniper
End of changes. 30 change blocks.
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