draft-ietf-rtgwg-rlfa-node-protection-11.txt   draft-ietf-rtgwg-rlfa-node-protection-12.txt 
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Intended status: Standards Track S. Hegde Intended status: Standards Track S. Hegde
Expires: July 24, 2017 C. Bowers Expires: July 24, 2017 C. Bowers
Juniper Networks, Inc. Juniper Networks, Inc.
H. Gredler H. Gredler
RtBrick, Inc. RtBrick, Inc.
S. Litkowski S. Litkowski
Orange Orange
January 20, 2017 January 20, 2017
Remote-LFA Node Protection and Manageability Remote-LFA Node Protection and Manageability
draft-ietf-rtgwg-rlfa-node-protection-11 draft-ietf-rtgwg-rlfa-node-protection-12
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 an extension to the Remote Loop-Free based IP This document describes procedures for determining if a given PQ-node
fast reroute mechanisms described in [RFC7490], that describes provides node-protection for a specific destination or not. The
procedures for determining if a given PQ-node provides node- document also shows how the same procedure can be utilized for
protection for a specific destination or not. The document also collection of complete characteristics for alternate paths.
shows how the same procedure can be utilized for collection of Knowledge about the characteristics of all alternate path is
complete characteristics for alternate paths. Knowledge about the precursory to apply operator defined policy for eliminating paths not
characteristics of all alternate path is precursory to apply operator fitting constraints.
defined policy for eliminating paths not fitting constraints.
Requirements Language Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119]. document are to be interpreted as described in RFC2119 [RFC2119].
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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destinations . . . . . . . . . . . . . . . . . . . . 11 destinations . . . . . . . . . . . . . . . . . . . . 11
2.3.3. Computing Node-Protecting R-LFA Paths for 2.3.3. Computing Node-Protecting R-LFA Paths for
Destinations with ECMP primary nexthop nodes . . . . 13 Destinations with ECMP primary nexthop nodes . . . . 13
2.3.4. Limiting extra computational overhead . . . . . . . . 17 2.3.4. Limiting extra computational overhead . . . . . . . . 17
3. Manageability of Remote-LFA Alternate Paths . . . . . . . . . 18 3. Manageability of Remote-LFA Alternate Paths . . . . . . . . . 18
3.1. The Problem . . . . . . . . . . . . . . . . . . . . . . . 18 3.1. The Problem . . . . . . . . . . . . . . . . . . . . . . . 18
3.2. The Solution . . . . . . . . . . . . . . . . . . . . . . 19 3.2. The Solution . . . . . . . . . . . . . . . . . . . . . . 19
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 19 6. Security Considerations . . . . . . . . . . . . . . . . . . . 19
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.1. Normative References . . . . . . . . . . . . . . . . . . 19 7.1. Normative References . . . . . . . . . . . . . . . . . . 20
7.2. Informative References . . . . . . . . . . . . . . . . . 20 7.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
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 Remote-LFA
failure of the primary nexthop node. Neither does the specification alternate, in case of failure of the primary nexthop node. Neither
provide a means to determine the same. does the specification provide a means to determine the same.
Also, the LFA Manageability [RFC7916] document requires a computing Also, the LFA Manageability [RFC7916] document requires a computing
router to find all possible (including all possible Remote-LFA) router to find all possible (including all possible Remote-LFA)
alternate nexthops, collect the complete set of path characteristics alternate nexthops, collect the complete set of path characteristics
for each alternate path, run an alternate-selection policy for each alternate path, run an alternate-selection policy
(configured by the operator) and find the best alternate path. This (configured by the operator) and find the best alternate path. This
will require the Remote-LFA implementation to gather all the required will require the Remote-LFA implementation to gather all the required
path characteristics along each link on the entire Remote-LFA path characteristics along each link on the entire Remote-LFA
alternate path. alternate path.
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This document describes a procedure for determining node-protection This document describes a procedure for determining node-protection
with Remote-LFA. The same procedure is also extended for collection with Remote-LFA. The same procedure is also extended for collection
of a complete set of path attributes, enabling more accurate policy- of a complete set of path attributes, enabling more accurate policy-
based selection for alternate paths obtained with Remote-LFA. based selection for alternate paths obtained with Remote-LFA.
1.1. Abbreviations 1.1. Abbreviations
This document uses the following list of abbreviations. This document uses the following list of abbreviations.
LFA - Loop Free Alternates LFA - Loop Free Alternates
RLFA or R-LFA - Remote Loop Free Alternates
RLFA or R-LFA - Remote Loop Free Alternates
ECMP - Equal Cost Multiple Path ECMP - Equal Cost Multiple Path
SPF - Shortest Path First graph computations SPF - Shortest Path First graph computations
NH - Next Hop node NH - Next Hop node
2. Node Protection with Remote-LFA 2. Node Protection with Remote-LFA
Node-protection is required to provide protection of traffic on a Node-protection is required to provide protection of traffic on a
given forwarding node, against the failure of the first-hop node on given forwarding node, against the failure of the first-hop node on
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Once a subset of PQ-nodes is found, computing router shall run a Once a subset of PQ-nodes is found, computing router shall run a
forward SPF on each of the PQ-nodes in the subset to continue with forward SPF on each of the PQ-nodes in the subset to continue with
procedures proposed in Section 2.3.2. procedures proposed in Section 2.3.2.
3. Manageability of Remote-LFA Alternate Paths 3. Manageability of Remote-LFA Alternate Paths
3.1. The Problem 3.1. The Problem
With the regular Remote-LFA [RFC7490] functionality the computing With the regular Remote-LFA [RFC7490] functionality the computing
router may compute more than one PQ-node as usable Remote-LFA router may compute more than one PQ-node as usable Remote-LFA
alternate nexthops. Additionally an alternate selection policy may alternate nexthops. Additionally [RFC7916] specifies a LFA (and
be configured to enable the network operator to choose one of them as Remote-LFA) manageability framework, in which an alternate selection
the most appropriate Remote-LFA alternate. For such policy-based policy may be configured to let the network operator choose one of
alternate selection to run, all the relevant path characteristics for them as the most appropriate Remote-LFA alternate. For such policy-
each the alternate paths (one through each of the PQ-nodes), needs to based alternate selection to run, the computing router needs to
be collected. As mentioned before in Section 2.3 the R-LFA alternate collect all the relevant path characteristics (as specified in
path through a given PQ-node to a given destination is comprised of section 6.2.4 of [RFC7916]) for each of the alternate paths (one
two path segments. through each of the PQ-nodes). As mentioned before in Section 2.3
the R-LFA alternate path through a given PQ-node to a given
destination is comprised of two path segments. Section 6.2.5.4 of
[RFC7916] specifies that any kind of alternate selection policy must
consider path characteristics for both path segments while evaluating
one or more RLFA alternate path(s).
The first path segment (i.e. from the computing router to the PQ- The first path segment (i.e. from the computing router to the PQ-
node) can be calculated from the regular forward SPF done as part of node) can be calculated from the regular forward SPF done as part of
standard and remote LFA computations. However without the mechanism standard and remote LFA computations. However without the mechanism
proposed in section Section 2.3.2 of this document, there is no way proposed in Section 2.3.2 of this document, there is no way to
to determine the path characteristics for the second path segment determine the path characteristics for the second path segment (i.e.
(i.e. from the PQ-node to the destination). In the absence of the from the PQ-node to the destination). In the absence of the path
path characteristics for the second path segment, two Remote-LFA characteristics for the second path segment, two Remote-LFA alternate
alternate paths may be equally preferred based on the first path paths may be equally preferred based on the first path segments
segments characteristics only, although the second path segment characteristics only, although the second path segment attributes may
attributes may be different. be different.
3.2. The Solution 3.2. The Solution
The additional forward SPF computation proposed in Section 2.3.2 The additional forward SPF computation proposed in Section 2.3.2
document shall also collect links, nodes and path characteristics document shall also collect links, nodes and path characteristics
along the second path segment. This shall enable collection of along the second path segment. This shall enable collection of
complete path characteristics for a given Remote-LFA alternate path complete path characteristics for a given Remote-LFA alternate path
to a given destination. The complete alternate path characteristics to a given destination. The complete alternate path characteristics
shall then facilitate more accurate alternate path selection while shall then facilitate more accurate alternate path selection while
running the alternate selection policy. running the alternate selection policy.
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subset. The detailed suggestion on how to select this subset is subset. The detailed suggestion on how to select this subset is
specified in the same section. While this limits the number of specified in the same section. While this limits the number of
possible alternate paths provided to the alternate-selection policy, possible alternate paths provided to the alternate-selection policy,
this is needed to keep the computational complexity within affordable this is needed to keep the computational complexity within affordable
limits. However if the alternate-selection policy is very limits. However if the alternate-selection policy is very
restrictive this may leave few destinations in the entire topology restrictive this may leave few destinations in the entire topology
without protection. Yet this limitation provides a necessary without protection. Yet this limitation provides a necessary
tradeoff between extensive coverage and immense computational tradeoff between extensive coverage and immense computational
overhead. overhead.
The mechanism proposed in this section does not modify or invalidate
[RFC7916] or any parts of it. This document specifies a mechanism to
meet the requirements specified in section 6.5.2.4 in [RFC7916].
4. Acknowledgements 4. Acknowledgements
Many thanks to Bruno Decraene for providing his useful comments. We Many thanks to Bruno Decraene for providing his useful comments. We
would also like to thank Uma Chunduri for reviewing this document and would also like to thank Uma Chunduri for reviewing this document and
providing valuable feedback. Also, many thanks to Harish Raghuveer providing valuable feedback. Also, many thanks to Harish Raghuveer
for his review and comments on the initial versions of this document. for his review and comments on the initial versions of this document.
5. IANA Considerations 5. IANA Considerations
N/A. - No protocol changes are proposed in this document. N/A. - No protocol changes are proposed in this document.
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