draft-ietf-rtgwg-rlfa-node-protection-04.txt   draft-ietf-rtgwg-rlfa-node-protection-05.txt 
Routing Area Working Group P. Sarkar, Ed. Routing Area Working Group P. Sarkar, Ed.
Internet-Draft S. Hegde Internet-Draft S. Hegde
Intended status: Standards Track C. Bowers Intended status: Standards Track C. Bowers
Expires: April 16, 2016 Juniper Networks, Inc. Expires: June 12, 2016 Juniper Networks, Inc.
H. Gredler H. Gredler
Unaffiliated Unaffiliated
S. Litkowski S. Litkowski
Orange Orange
October 14, 2015 December 10, 2015
Remote-LFA Node Protection and Manageability Remote-LFA Node Protection and Manageability
draft-ietf-rtgwg-rlfa-node-protection-04 draft-ietf-rtgwg-rlfa-node-protection-05
Abstract Abstract
The loop-free alternates computed following the current Remote-LFA The loop-free alternates computed following the current Remote-LFA
[RFC7490] specification guarantees only link-protection. The specification guarantees only link-protection. The resulting Remote-
resulting Remote-LFA nexthops (also called PQ-nodes), may not LFA nexthops (also called PQ-nodes), may not guarantee node-
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
document also shows how the same procedure can be utilised for document also shows how the same procedure can be utilised for
collection of complete characteristics for alternate paths. collection of complete characteristics for alternate paths.
Knowledge about the characteristics of all alternate path is Knowledge about the characteristics of all alternate path is
precursory to apply operator defined policy for eliminating paths not precursory to apply operator defined policy for eliminating paths not
fitting constraints. fitting constraints.
Requirements Language Requirements Language
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This Internet-Draft will expire on April 16, 2016. This Internet-Draft will expire on June 12, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 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
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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 . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Node Protection with Remote-LFA . . . . . . . . . . . . . . . 3 2. Node Protection with Remote-LFA . . . . . . . . . . . . . . . 3
2.1. The Problem . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. The Problem . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Few Additional Definitions . . . . . . . . . . . . . . . 5 2.2. Additional Definitions . . . . . . . . . . . . . . . . . 6
2.2.1. Link-Protecting Extended P-Space . . . . . . . . . . 6 2.2.1. Link-Protecting Extended P-Space . . . . . . . . . . 6
2.2.2. Node-Protecting Extended P-Space . . . . . . . . . . 6 2.2.2. Node-Protecting Extended P-Space . . . . . . . . . . 6
2.2.3. Q-Space . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.3. Q-Space . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.4. Link-Protecting PQ Space . . . . . . . . . . . . . . 8 2.2.4. Link-Protecting PQ Space . . . . . . . . . . . . . . 6
2.2.5. Candidate Node-Protecting PQ Space . . . . . . . . . 8 2.2.5. Candidate Node-Protecting PQ Space . . . . . . . . . 7
2.3. Computing Node-protecting R-LFA Path . . . . . . . . . . 8 2.2.6. Cost-Based Definitions . . . . . . . . . . . . . . . 7
2.2.6.1. Link-Protecting Extended P-Space . . . . . . . . 7
2.2.6.2. Node-Protecting Extended P-Space . . . . . . . . 7
2.2.6.3. Q-Space . . . . . . . . . . . . . . . . . . . . . 8
2.3. Computing Node-protecting R-LFA Path . . . . . . . . . . 9
2.3.1. Computing Candidate Node-protecting PQ-Nodes for 2.3.1. Computing Candidate Node-protecting PQ-Nodes for
Primary nexthops . . . . . . . . . . . . . . . . . . 8 Primary nexthops . . . . . . . . . . . . . . . . . . 9
2.3.2. Computing node-protecting paths from PQ-nodes to 2.3.2. Computing node-protecting paths from PQ-nodes to
destinations . . . . . . . . . . . . . . . . . . . . 10 destinations . . . . . . . . . . . . . . . . . . . . 11
2.3.3. Limiting extra computational overhead . . . . . . . . 12 2.3.3. Limiting extra computational overhead . . . . . . . . 13
3. Manageabilty of Remote-LFA Alternate Paths . . . . . . . . . 13 3. Manageabilty of Remote-LFA Alternate Paths . . . . . . . . . 14
3.1. The Problem . . . . . . . . . . . . . . . . . . . . . . . 13 3.1. The Problem . . . . . . . . . . . . . . . . . . . . . . . 14
3.2. The Solution . . . . . . . . . . . . . . . . . . . . . . 14 3.2. The Solution . . . . . . . . . . . . . . . . . . . . . . 15
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1. Normative References . . . . . . . . . . . . . . . . . . 15 7.1. Normative References . . . . . . . . . . . . . . . . . . 15
7.2. Informative References . . . . . . . . . . . . . . . . . 15 7.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
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.
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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. Few 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] draft. 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] draft already defines this. The link- The Remote-LFA [RFC7490] specification already defines this. The
protecting extended P-space for a link S-E being protected is the set link-protecting extended P-space for a link S-E being protected is
of routers that are reachable from one or more direct neighbors of S, the set of routers that are reachable from one or more direct
except primary node E, without traversing the S-E link on any of the neighbors of S, except primary node E, without traversing the S-E
shortest path from the direct neighbor to the router. This MUST link on any of the shortest path from the direct neighbor to the
exclude any direct neighbor for which there is at least one ECMP path router. This MUST exclude any direct neighbor for which there is at
from the direct neighbor traversing the link(S-E) being protected. least one ECMP path from the direct neighbor traversing the link(S-E)
being protected.
For a cost-based definition for Link-protecting Extended P-Space
refer to Section 2.2.6.1.
2.2.2. Node-Protecting Extended P-Space
The node-protecting extended P-space for a primary nexthop node E
being protected, is the set of routers that are reachable from one or
more direct neighbors of S, except primary node E, without traversing
the node E. This MUST exclude any direct neighbors for which there
is at least one ECMP path from the direct neighbor traversing the
node E being protected.
For a cost-based definition for Node-protecting Extended P-Space
refer to Section 2.2.6.2.
2.2.3. Q-Space
The Remote-LFA [RFC7490] draft already defines this. The Q-space for
a link S-E being protected is the set of routers that can reach
primary node E, without traversing the S-E link on any of the
shortest path from the node Y to primary nexthop E. This MUST
exclude any destination for which there is at least one ECMP path
from the node Y to the primary nexthop E traversing the link(S-E)
being protected.
For a cost-based definition for Q-Space refer to Section 2.2.6.3.
2.2.4. Link-Protecting PQ Space
A node Y is in link-protecting PQ space w.r.t to the link (S-E) being
protected, if and only if, Y is present in both link-protecting
extended P-space and the Q-space for the link being protected.
2.2.5. Candidate Node-Protecting PQ Space
A node Y is in candidate node-protecting PQ space w.r.t to the node
(E) being protected, if and only if, Y is present in both node-
protecting extended P-space and the Q-space for the link being
protected.
It must be noted, that a node Y being in candidate node-protecting
PQ-space, does not guarantee that the R-LFA alternate path via the
same, in entirety, is unaffected in the event of a node failure of
primary nexthop node E. It only guarantees that the path segment
from S to PQ-node Y is unaffected by the same failure event. The PQ-
nodes in the candidate node-protecting PQ space may provide node
protection for only a subset of destinations that are reachable
through the corresponding primary link.
2.2.6. Cost-Based Definitions
This section provides cost-based definitions for some of the terms
introduced in Section 2.2 of this document.
2.2.6.1. Link-Protecting Extended P-Space
Please refer to Section 2.2.1 for a formal definition for Link-
protecting Extended P-Space.
A node Y is in link-protecting extended P-space w.r.t to the link A node Y is in link-protecting extended P-space w.r.t to the link
(S-E) being protected, if and only if, there exists at least one (S-E) being protected, if and only if, there exists at least one
direct neighbor of S, Ni, other than primary nexthop E, that direct neighbor of S, Ni, other than primary nexthop E, that
satisfies the following condition. satisfies the following condition.
D_opt(Ni,Y) < D_opt(Ni,S) + D_opt(S,Y) D_opt(Ni,Y) < D_opt(Ni,S) + D_opt(S,Y)
Where, Where,
D_opt(A,B) : Distance on most optimum path from A to B. D_opt(A,B) : Distance on most optimum path from A to B.
Ni : A direct neighbor of S other than primary Ni : A direct neighbor of S other than primary
nexthop E. nexthop E.
Y : The node being evaluated for link-protecting Y : The node being evaluated for link-protecting
extended P-Space. extended P-Space.
Figure 3: Link-Protecting Ext-P-Space Condition Figure 3: Link-Protecting Ext-P-Space Condition
2.2.2. Node-Protecting Extended P-Space 2.2.6.2. Node-Protecting Extended P-Space
The node-protecting extended P-space for a primary nexthop node E Please refer to Section 2.2.2 for a formal definition for Node-
being protected, is the set of routers that are reachable from one or protecting Extended P-Space.
more direct neighbors of S, except primary node E, without traversing
the node E. This MUST exclude any direct neighbors for which there
is at least one ECMP path from the direct neighbor traversing the
node E being protected.
A node Y is in node-protecting extended P-space w.r.t to the node E A node Y is in node-protecting extended P-space w.r.t to the node E
being protected, if and only if, there exists at least one direct being protected, if and only if, there exists at least one direct
neighbor of S, Ni, other than primary nexthop E, that satisfies the neighbor of S, Ni, other than primary nexthop E, that satisfies the
following condition. following condition.
D_opt(Ni,Y) < D_opt(Ni,E) + D_opt(E,Y) D_opt(Ni,Y) < D_opt(Ni,E) + D_opt(E,Y)
Where, Where,
D_opt(A,B) : Distance on most optimum path from A to B. D_opt(A,B) : Distance on most optimum path from A to B.
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Figure 4: Node-Protecting Ext-P-Space Condition Figure 4: Node-Protecting Ext-P-Space Condition
It must be noted that a node Y satisfying the condition in Figure 4 It must be noted that a node Y satisfying the condition in Figure 4
above only guarantees that the R-LFA alternate path segment from S above only guarantees that the R-LFA alternate path segment from S
via direct neighbor Ni to the node Y is not affected in the event of via direct neighbor Ni to the node Y is not affected in the event of
a node failure of E. It does not yet guarantee that the path segment a node failure of E. It does not yet guarantee that the path segment
from node Y to the destination is also unaffected by the same failure from node Y to the destination is also unaffected by the same failure
event. event.
2.2.3. Q-Space 2.2.6.3. Q-Space
The Remote-LFA [RFC7490] draft already defines this. The Q-space for Please refer to Section 2.2.3 for a formal definition for Q-Space.
a link S-E being protected is the set of routers that can reach
primary node E, without traversing the S-E link on any of the
shortest path from the node Y to primary nexthop E. This MUST
exclude any destination for which there is at least one ECMP path
from the node Y to the primary nexthop E traversing the link(S-E)
being protected.
A node Y is in Q-space w.r.t to the link (S-E) being protected, if A node Y is in Q-space w.r.t to the link (S-E) being protected, if
and only if, the following condition is satisfied. and only if, the following condition is satisfied.
D_opt(Y,E) < D_opt(S,E) + D_opt(Y,S) D_opt(Y,E) < D_opt(S,E) + D_opt(Y,S)
Where, Where,
D_opt(A,B) : Distance on most optimum path from A to B. D_opt(A,B) : Distance on most optimum path from A to B.
E : The primary nexthop on shortest path from S E : The primary nexthop on shortest path from S
to destination. to destination.
Y : The node being evaluated for Q-Space. Y : The node being evaluated for Q-Space.
Figure 5: Q-Space Condition Figure 5: Q-Space Condition
2.2.4. Link-Protecting PQ Space
A node Y is in link-protecting PQ space w.r.t to the link (S-E) being
protected, if and only if, Y is present in both link-protecting
extended P-space and the Q-space for the link being protected.
2.2.5. Candidate Node-Protecting PQ Space
A node Y is in candidate node-protecting PQ space w.r.t to the node
(E) being protected, if and only if, Y is present in both node-
protecting extended P-space and the Q-space for the link being
protected.
Again it must be noted that a node Y being in candidate node-
protecting PQ-space does not guarantee that the R-LFA alternate path
via the same, in entirety, is unaffected in the event of a node
failure of primary nexthop node E. It only guarantees that the path
segment from S to PQ-node Y is unaffected by the same failure event.
The PQ-nodes in the candidate node-protecting PQ space may provide
node protection for only a subset of destinations that are reachable
through the corresponding primary link.
2.3. Computing Node-protecting R-LFA Path 2.3. Computing Node-protecting R-LFA Path
The R-LFA alternate path through a given PQ-node to a given The R-LFA alternate path through a given PQ-node to a given
destination is comprised of two path segments as follows. destination is comprised of two path segments as follows.
1. Path segment from the computing router to the PQ-node (Remote-LFA 1. Path segment from the computing router to the PQ-node (Remote-LFA
alternate nexthop), and alternate nexthop), and
2. Path segment from the PQ-node to the destination being protected. 2. Path segment from the PQ-node to the destination being protected.
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