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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 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. 
129 lines changed or deleted 146 lines changed or added

This html diff was produced by rfcdiff 1.42. The latest version is available from http://tools.ietf.org/tools/rfcdiff/