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 | |||

skipping to change at page 2, line 7 | skipping to change at page 2, line 7 | |||

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 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 | |||

(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 | |||

skipping to change at page 2, line 29 | skipping to change at page 2, line 29 | |||

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. | |||

skipping to change at page 5, line 45 | skipping to change at page 6, line 5 | |||

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. | |||

skipping to change at page 7, line 25 | skipping to change at page 8, line 30 | |||

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. | |||

End of changes. 18 change blocks. | ||||

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