 1/draftietfrtgwgrlfanodeprotection04.txt 20151210 04:15:30.465634846 0800
+++ 2/draftietfrtgwgrlfanodeprotection05.txt 20151210 04:15:30.509635906 0800
@@ 1,30 +1,30 @@
Routing Area Working Group P. Sarkar, Ed.
InternetDraft S. Hegde
Intended status: Standards Track C. Bowers
Expires: April 16, 2016 Juniper Networks, Inc.
+Expires: June 12, 2016 Juniper Networks, Inc.
H. Gredler
Unaffiliated
S. Litkowski
Orange
 October 14, 2015
+ December 10, 2015
RemoteLFA Node Protection and Manageability
 draftietfrtgwgrlfanodeprotection04
+ draftietfrtgwgrlfanodeprotection05
Abstract
The loopfree alternates computed following the current RemoteLFA
 [RFC7490] specification guarantees only linkprotection. The
 resulting RemoteLFA nexthops (also called PQnodes), may not
 guarantee nodeprotection for all destinations being protected by it.
+ specification guarantees only linkprotection. The resulting Remote
+ LFA nexthops (also called PQnodes), may not guarantee node
+ protection for all destinations being protected by it.
This document describes procedures for determining if a given PQnode
provides nodeprotection for a specific destination or not. The
document also shows how the same procedure can be utilised for
collection of complete characteristics for alternate paths.
Knowledge about the characteristics of all alternate path is
precursory to apply operator defined policy for eliminating paths not
fitting constraints.
Requirements Language
@@ 41,21 +41,21 @@
InternetDrafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as InternetDrafts. The list of current Internet
Drafts is at http://datatracker.ietf.org/drafts/current/.
InternetDrafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use InternetDrafts as reference
material or to cite them other than as "work in progress."
 This InternetDraft will expire on April 16, 2016.
+ This InternetDraft will expire on June 12, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/licenseinfo) in effect on the date of
publication of this document. Please review these documents
@@ 63,42 +63,46 @@
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Node Protection with RemoteLFA . . . . . . . . . . . . . . . 3
2.1. The Problem . . . . . . . . . . . . . . . . . . . . . . . 4
 2.2. Few Additional Definitions . . . . . . . . . . . . . . . 5
+ 2.2. Additional Definitions . . . . . . . . . . . . . . . . . 6
2.2.1. LinkProtecting Extended PSpace . . . . . . . . . . 6
2.2.2. NodeProtecting Extended PSpace . . . . . . . . . . 6
 2.2.3. QSpace . . . . . . . . . . . . . . . . . . . . . . . 7
 2.2.4. LinkProtecting PQ Space . . . . . . . . . . . . . . 8
 2.2.5. Candidate NodeProtecting PQ Space . . . . . . . . . 8
 2.3. Computing Nodeprotecting RLFA Path . . . . . . . . . . 8
+ 2.2.3. QSpace . . . . . . . . . . . . . . . . . . . . . . . 6
+ 2.2.4. LinkProtecting PQ Space . . . . . . . . . . . . . . 6
+ 2.2.5. Candidate NodeProtecting PQ Space . . . . . . . . . 7
+ 2.2.6. CostBased Definitions . . . . . . . . . . . . . . . 7
+ 2.2.6.1. LinkProtecting Extended PSpace . . . . . . . . 7
+ 2.2.6.2. NodeProtecting Extended PSpace . . . . . . . . 7
+ 2.2.6.3. QSpace . . . . . . . . . . . . . . . . . . . . . 8
+ 2.3. Computing Nodeprotecting RLFA Path . . . . . . . . . . 9
2.3.1. Computing Candidate Nodeprotecting PQNodes for
 Primary nexthops . . . . . . . . . . . . . . . . . . 8
+ Primary nexthops . . . . . . . . . . . . . . . . . . 9
2.3.2. Computing nodeprotecting paths from PQnodes to
 destinations . . . . . . . . . . . . . . . . . . . . 10
 2.3.3. Limiting extra computational overhead . . . . . . . . 12
 3. Manageabilty of RemoteLFA Alternate Paths . . . . . . . . . 13
 3.1. The Problem . . . . . . . . . . . . . . . . . . . . . . . 13
 3.2. The Solution . . . . . . . . . . . . . . . . . . . . . . 14
 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
+ destinations . . . . . . . . . . . . . . . . . . . . 11
+ 2.3.3. Limiting extra computational overhead . . . . . . . . 13
+ 3. Manageabilty of RemoteLFA Alternate Paths . . . . . . . . . 14
+ 3.1. The Problem . . . . . . . . . . . . . . . . . . . . . . . 14
+ 3.2. The Solution . . . . . . . . . . . . . . . . . . . . . . 15
+ 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
+ 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
+ 6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
+ 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1. Normative References . . . . . . . . . . . . . . . . . . 15
 7.2. Informative References . . . . . . . . . . . . . . . . . 15
 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
+ 7.2. Informative References . . . . . . . . . . . . . . . . . 16
+ Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
The RemoteLFA [RFC7490] specification provides loopfree alternates
that guarantee only linkprotection. The resulting RemoteLFA
alternate nexthops (also referred to as the PQnodes) may not provide
nodeprotection for all destinations covered by the same, in case of
failure of the primary nexthop node. Neither does the specification
provide a means to determine the same.
@@ 221,59 +225,115 @@
single PQnode R2 provided nodeprotection for destinations R3 and
D2, if we choose R3 as the RLFA nexthop, it does not provide node
protection for R3 and D2 anymore. If S chooses R3 as the RLFA
nexthop, in the event of the nodefailure on primary nexthop E, on
the alternate path from S to RLFA nexthop R3, one of parallel ECMP
path between N and R3 also becomes unavailable. So for a RemoteLFA
nexthop to provide nodeprotection for a given destination, it is
also mandatory that, the shortest path from S to the chosen PQnode
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
 the ones mentioned in RemoteLFA [RFC7490] draft.
+ the ones mentioned in RemoteLFA [RFC7490] specification.
2.2.1. LinkProtecting Extended PSpace
 The RemoteLFA [RFC7490] draft already defines this. The link
 protecting extended Pspace for a link SE 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 SE link on any of the
 shortest path from the direct neighbor to the router. This MUST
 exclude any direct neighbor for which there is at least one ECMP path
 from the direct neighbor traversing the link(SE) being protected.
+ The RemoteLFA [RFC7490] specification already defines this. The
+ linkprotecting extended Pspace for a link SE 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 SE
+ link on any of the shortest path from the direct neighbor to the
+ router. This MUST exclude any direct neighbor for which there is at
+ least one ECMP path from the direct neighbor traversing the link(SE)
+ being protected.
+
+ For a costbased definition for Linkprotecting Extended PSpace
+ refer to Section 2.2.6.1.
+
+2.2.2. NodeProtecting Extended PSpace
+
+ The nodeprotecting extended Pspace 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 costbased definition for Nodeprotecting Extended PSpace
+ refer to Section 2.2.6.2.
+
+2.2.3. QSpace
+
+ The RemoteLFA [RFC7490] draft already defines this. The Qspace for
+ a link SE being protected is the set of routers that can reach
+ primary node E, without traversing the SE 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(SE)
+ being protected.
+
+ For a costbased definition for QSpace refer to Section 2.2.6.3.
+
+2.2.4. LinkProtecting PQ Space
+
+ A node Y is in linkprotecting PQ space w.r.t to the link (SE) being
+ protected, if and only if, Y is present in both linkprotecting
+ extended Pspace and the Qspace for the link being protected.
+
+2.2.5. Candidate NodeProtecting PQ Space
+
+ A node Y is in candidate nodeprotecting PQ space w.r.t to the node
+ (E) being protected, if and only if, Y is present in both node
+ protecting extended Pspace and the Qspace for the link being
+ protected.
+
+ It must be noted, that a node Y being in candidate nodeprotecting
+ PQspace, does not guarantee that the RLFA 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 PQnode Y is unaffected by the same failure event. The PQ
+ nodes in the candidate nodeprotecting PQ space may provide node
+ protection for only a subset of destinations that are reachable
+ through the corresponding primary link.
+
+2.2.6. CostBased Definitions
+
+ This section provides costbased definitions for some of the terms
+ introduced in Section 2.2 of this document.
+
+2.2.6.1. LinkProtecting Extended PSpace
+
+ Please refer to Section 2.2.1 for a formal definition for Link
+ protecting Extended PSpace.
A node Y is in linkprotecting extended Pspace w.r.t to the link
(SE) being protected, if and only if, there exists at least one
direct neighbor of S, Ni, other than primary nexthop E, that
satisfies the following condition.
D_opt(Ni,Y) < D_opt(Ni,S) + D_opt(S,Y)
Where,
D_opt(A,B) : Distance on most optimum path from A to B.
Ni : A direct neighbor of S other than primary
nexthop E.
Y : The node being evaluated for linkprotecting
extended PSpace.
Figure 3: LinkProtecting ExtPSpace Condition
2.2.2. NodeProtecting Extended PSpace
+2.2.6.2. NodeProtecting Extended PSpace
 The nodeprotecting extended Pspace 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.
+ Please refer to Section 2.2.2 for a formal definition for Node
+ protecting Extended PSpace.
A node Y is in nodeprotecting extended Pspace w.r.t to the node E
being protected, if and only if, there exists at least one direct
neighbor of S, Ni, other than primary nexthop E, that satisfies the
following condition.
D_opt(Ni,Y) < D_opt(Ni,E) + D_opt(E,Y)
Where,
D_opt(A,B) : Distance on most optimum path from A to B.
@@ 286,65 +346,37 @@
Figure 4: NodeProtecting ExtPSpace Condition
It must be noted that a node Y satisfying the condition in Figure 4
above only guarantees that the RLFA alternate path segment from S
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
from node Y to the destination is also unaffected by the same failure
event.
2.2.3. QSpace
+2.2.6.3. QSpace
 The RemoteLFA [RFC7490] draft already defines this. The Qspace for
 a link SE being protected is the set of routers that can reach
 primary node E, without traversing the SE 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(SE)
 being protected.
+ Please refer to Section 2.2.3 for a formal definition for QSpace.
A node Y is in Qspace w.r.t to the link (SE) being protected, if
and only if, the following condition is satisfied.
D_opt(Y,E) < D_opt(S,E) + D_opt(Y,S)
Where,
D_opt(A,B) : Distance on most optimum path from A to B.
E : The primary nexthop on shortest path from S
to destination.
Y : The node being evaluated for QSpace.
Figure 5: QSpace Condition
2.2.4. LinkProtecting PQ Space

 A node Y is in linkprotecting PQ space w.r.t to the link (SE) being
 protected, if and only if, Y is present in both linkprotecting
 extended Pspace and the Qspace for the link being protected.

2.2.5. Candidate NodeProtecting PQ Space

 A node Y is in candidate nodeprotecting PQ space w.r.t to the node
 (E) being protected, if and only if, Y is present in both node
 protecting extended Pspace and the Qspace for the link being
 protected.

 Again it must be noted that a node Y being in candidate node
 protecting PQspace does not guarantee that the RLFA 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 PQnode Y is unaffected by the same failure event.
 The PQnodes in the candidate nodeprotecting PQ space may provide
 node protection for only a subset of destinations that are reachable
 through the corresponding primary link.

2.3. Computing Nodeprotecting RLFA Path
The RLFA alternate path through a given PQnode to a given
destination is comprised of two path segments as follows.
1. Path segment from the computing router to the PQnode (RemoteLFA
alternate nexthop), and
2. Path segment from the PQnode to the destination being protected.