draft-ietf-rtgwg-rlfa-node-protection-06.txt   draft-ietf-rtgwg-rlfa-node-protection-07.txt 
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Intended status: Standards Track S. Hegde Intended status: Standards Track S. Hegde
Expires: April 11, 2017 C. Bowers Expires: April 11, 2017 C. Bowers
Juniper Networks, Inc. Juniper Networks, Inc.
H. Gredler H. Gredler
RtBrick Inc. RtBrick Inc.
S. Litkowski S. Litkowski
Orange Orange
October 8, 2016 October 8, 2016
Remote-LFA Node Protection and Manageability Remote-LFA Node Protection and Manageability
draft-ietf-rtgwg-rlfa-node-protection-06 draft-ietf-rtgwg-rlfa-node-protection-07
Abstract Abstract
The loop-free alternates computed following the current Remote-LFA The loop-free alternates computed following the current Remote-LFA
specification guarantees only link-protection. The resulting Remote- specification guarantees only link-protection. The resulting Remote-
LFA nexthops (also called PQ-nodes), may not guarantee node- LFA nexthops (also called PQ-nodes), may not guarantee node-
protection for all destinations being protected by it. protection for all destinations being protected by it.
This document describes procedures for determining if a given PQ-node This document describes procedures for determining if a given PQ-node
provides node-protection for a specific destination or not. The provides node-protection for a specific destination or not. The
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1. Introduction 1. Introduction
The Remote-LFA [RFC7490] specification provides loop-free alternates The Remote-LFA [RFC7490] specification provides loop-free alternates
that guarantee only link-protection. The resulting Remote-LFA that guarantee only link-protection. The resulting Remote-LFA
alternate nexthops (also referred to as the PQ-nodes) may not provide alternate nexthops (also referred to as the PQ-nodes) may not provide
node-protection for all destinations covered by the same, in case of node-protection for all destinations covered by the same, in case of
failure of the primary nexthop node. Neither does the specification failure of the primary nexthop node. Neither does the specification
provide a means to determine the same. provide a means to determine the same.
Also, the LFA Manageability [I-D.ietf-rtgwg-lfa-manageability] Also, the LFA Manageability [RFC7916] document, requires a computing
document, requires a computing router to find all possible (including router to find all possible (including all possible Remote-LFA)
all possible Remote-LFA) alternate nexthops, collect the complete set alternate nexthops, collect the complete set of path characteristics
of path characteristics for each alternate path, run a alternate- for each alternate path, run a alternate-selection policy (configured
selection policy (configured by the operator), and find the best by the operator), and find the best alternate path. This will
alternate path. This will require the Remote-LFA implementation to require the Remote-LFA implementation to gather all the required path
gather all the required path characteristics along each link on the characteristics along each link on the entire Remote-LFA alternate
entire Remote-LFA alternate path. path.
With current LFA [RFC5286] and Remote-LFA implementations, the With current LFA [RFC5286] and Remote-LFA implementations, the
forward SPF (and reverse SPF) is run on the computing router and its forward SPF (and reverse SPF) is run on the computing router and its
immediate 1-hop routers as the roots. While that enables computation immediate 1-hop routers as the roots. While that enables computation
of path attributes (e.g. SRLG, Admin-groups) for first alternate of path attributes (e.g. SRLG, Admin-groups) for first alternate
path segment from the computing router to the PQ-node, there is no path segment from the computing router to the PQ-node, there is no
means for the computing router to gather any path attributes for the means for the computing router to gather any path attributes for the
path segment from the PQ-node to destination. Consequently any path segment from the PQ-node to destination. Consequently any
policy-based selection of alternate paths will consider only the path policy-based selection of alternate paths will consider only the path
attributes from the computing router up until the PQ-node. attributes from the computing router up until the PQ-node.
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Table 1: Remote-LFA backup paths via PQ-node R2 Table 1: Remote-LFA backup paths via PQ-node R2
A closer look at Table 1 shows that, while the PQ-node R2 provides A closer look at Table 1 shows that, while the PQ-node R2 provides
link-protection for all the destinations, it does not provide node- link-protection for all the destinations, it does not provide node-
protection for destinations E and D1. In the event of the node- protection for destinations E and D1. In the event of the node-
failure on primary nexthop E, the alternate path from Remote-LFA failure on primary nexthop E, the alternate path from Remote-LFA
nexthop R2 to E and D1 also becomes unavailable. So for a Remote-LFA nexthop R2 to E and D1 also becomes unavailable. So for a Remote-LFA
nexthop to provide node-protection for a given destination, it is nexthop to provide node-protection for a given destination, it is
mandatory that, the shortest path from the given PQ-node to the given mandatory that, the shortest path from the given PQ-node to the given
destination MUST not traverse the primary nexthop. destination MUST NOT traverse the primary nexthop.
In another extension of the topology in Figure 1 let us consider an In another extension of the topology in Figure 1 let us consider an
additional link between N and E with the same cost as the other additional link between N and E with the same cost as the other
links. links.
D1 D1
/ /
S-x-E S-x-E
/ / \ / / \
N---+ R3--D2 N---+ R3--D2
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Again a closer look at Table 2 shows that, unlike Table 1, where the Again a closer look at Table 2 shows that, unlike Table 1, where the
single PQ-node R2 provided node-protection for destinations R3 and single PQ-node R2 provided node-protection for destinations R3 and
D2, if we choose R3 as the R-LFA nexthop, it does not provide node- D2, if we choose R3 as the R-LFA nexthop, it does not provide node-
protection for R3 and D2 anymore. If S chooses R3 as the R-LFA protection for R3 and D2 anymore. If S chooses R3 as the R-LFA
nexthop, in the event of the node-failure on primary nexthop E, on nexthop, in the event of the node-failure on primary nexthop E, on
the alternate path from S to R-LFA nexthop R3, one of parallel ECMP the alternate path from S to R-LFA nexthop R3, one of parallel ECMP
path between N and R3 also becomes unavailable. So for a Remote-LFA path between N and R3 also becomes unavailable. So for a Remote-LFA
nexthop to provide node-protection for a given destination, it is nexthop to provide node-protection for a given destination, it is
also mandatory that, the shortest path from S to the chosen PQ-node also mandatory that, the shortest path from S to the chosen PQ-node
MUST not traverse the primary nexthop node. MUST NOT traverse the primary nexthop node.
2.2. Additional Definitions 2.2. Additional Definitions
This document adds and enhances the following definitions extending This document adds and enhances the following definitions extending
the ones mentioned in Remote-LFA [RFC7490] specification. the ones mentioned in Remote-LFA [RFC7490] specification.
2.2.1. Link-Protecting Extended P-Space 2.2.1. Link-Protecting Extended P-Space
The Remote-LFA [RFC7490] specification already defines this. The The Remote-LFA [RFC7490] specification already defines this. The
link-protecting extended P-space for a link S-E being protected is link-protecting extended P-space for a link S-E being protected is
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7.1. Normative References 7.1. Normative References
[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,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
7.2. Informative References 7.2. Informative References
[I-D.ietf-rtgwg-lfa-manageability]
Litkowski, S., Decraene, B., Filsfils, C., Raza, K., and
M. Horneffer, "Operational management of Loop Free
Alternates", draft-ietf-rtgwg-lfa-manageability-11 (work
in progress), June 2015.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for [RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
IP Fast Reroute: Loop-Free Alternates", RFC 5286, IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC5286, September 2008, DOI 10.17487/RFC5286, September 2008,
<http://www.rfc-editor.org/info/rfc5286>. <http://www.rfc-editor.org/info/rfc5286>.
[RFC7490] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N. [RFC7490] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)", So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
RFC 7490, DOI 10.17487/RFC7490, April 2015, RFC 7490, DOI 10.17487/RFC7490, April 2015,
<http://www.rfc-editor.org/info/rfc7490>. <http://www.rfc-editor.org/info/rfc7490>.
[RFC7916] Litkowski, S., Ed., Decraene, B., Filsfils, C., Raza, K.,
Horneffer, M., and P. Sarkar, "Operational Management of
Loop-Free Alternates", RFC 7916, DOI 10.17487/RFC7916,
July 2016, <http://www.rfc-editor.org/info/rfc7916>.
Authors' Addresses Authors' Addresses
Pushpasis Sarkar (editor) Pushpasis Sarkar (editor)
Individual Contributor Individual Contributor
Email: pushpasis.ietf@gmail.com Email: pushpasis.ietf@gmail.com
Shraddha Hegde Shraddha Hegde
Juniper Networks, Inc. Juniper Networks, Inc.
Electra, Exora Business Park Electra, Exora Business Park
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