PCE Working Group A. Tokar
Internet-Draft S. Sivabalan
Intended status: Standards Track Cisco Systems, Inc.
Expires: January 1, 2020 M. Negi
Huawei Technologies
June 30, 2019

Carrying SID Algorithm information in PCE-based Networks.


The Algorithm associated with a prefix Segment-ID (SID) defines the path computation Algorithm used by Interior Gateway Protocols (IGPs). This information is available to controllers such as the Path Computation Element (PCE) via topology learning. This document proposes an approach for informing headend routers regarding the Algorithm associated with each prefix SID used in PCE-computed paths.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on January 1, 2020.

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Table of Contents

1. Introduction

A PCE can compute SR-TE paths using prefix SIDs with different Algorithms depending on the use-case, constraints, etc. While this information is available on the PCE, there is no method of conveying this information to the headend router.

Similarly, the headend can also compute SR-TE paths using different Algorithms, and this information also needs to be conveyed to the PCE for collection or troubleshooting purposes. In addition, in the case of multiple (redundant) PCEs, when the headend receives a path from the primary PCE, it needs to be able to report the complete path information - including the Algorithm - to the backup PCE so that in HA scenarios, the backup PCE can verify the prefix SIDs appropriately.

Refer to [I-D.ietf-ospf-segment-routing-extensions] and [I-D.ietf-isis-segment-routing-extensions] for details about the prefix SID Algorithm.

This document introduces two new NAI types for the SR-ERO subobject, which is defined in [I-D.ietf-pce-segment-routing].

2. Terminology

The following terminologies are used in this document:

Explicit Route Object
Interior Gateway Protocol
Node or Adjacency Identifier.
Path Computation Element
Path Computation Element Protocol.
Segment Identifier.
Segment Routing.
Segment Routing Traffic Engineering.

3. SR ERO NAI Extensions

The SR-ERO subobject encoding is extended with additional NAI types.

The following new NAI types (NT) are defined:

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  |                      Node IPv4 address                        |
  |                  Reserved                     |  Algorithm    | 

Figure 1: NAI for IPv4 Node SID with Algorithm

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  //               Node IPv6 address (16 octets)                 //
  |                  Reserved                     |  Algorithm    | 

Figure 2: NAI for IPv6 Node SID with Algorithm

This document defines the following NAIs:

'IPv4 Node ID with Algorithm'
is specified as an IPv4 address and Algorithm identifier. In this case, the NT value is TBD1 and the NAI field length is 8 octets.
'IPv6 Node ID with Algorithm'
is specified as an IPv6 address and Algorithm identifier. In this case, the NT value is TBD2 and the NAI field length is 20 octets.

4. Operation

IPv4 prefix SIDs used by SR-TE paths with an associated Algorithm SHOULD be encoded with 'IPv4 Node ID with Algorithm' NAI.

IPv6 prefix SIDs used by SR-TE paths with an associated Algorithm SHOULD be encoded with 'IPv6 Node ID with Algorithm' NAI.

5. Security Considerations

No additional security measure is required.

6. IANA Considerations

6.1. PCEP SR-ERO NAI Types

IANA is requested to allocate new SR-ERO NAI types for the new NAI types specified in this document.

Value Description Reference
TBD1 IPv4 Node ID with Algorithm This document
TBD2 IPv6 Node ID with Algorithm This document

7. Normative References

[I-D.ietf-isis-segment-routing-extensions] Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., Gredler, H. and B. Decraene, "IS-IS Extensions for Segment Routing", Internet-Draft draft-ietf-isis-segment-routing-extensions-25, May 2019.
[I-D.ietf-ospf-segment-routing-extensions] Psenak, P., Previdi, S., Filsfils, C., Gredler, H., Shakir, R., Henderickx, W. and J. Tantsura, "OSPF Extensions for Segment Routing", Internet-Draft draft-ietf-ospf-segment-routing-extensions-27, December 2018.
[I-D.ietf-pce-segment-routing] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W. and J. Hardwick, "PCEP Extensions for Segment Routing", Internet-Draft draft-ietf-pce-segment-routing-16, March 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.

Authors' Addresses

Alex Tokar Cisco Systems, Inc. Eurovea Central 3. Pribinova 10 Bratislava, 811 09 Slovakia EMail: atokar@cisco.com
Siva Sivabalan Cisco Systems, Inc. 2000 Innovation Drive Kanata, Ontario K2K 3E8 Canada EMail: msiva@cisco.com
Mahendra Singh Negi Huawei Technologies Divyashree Techno Park, Whitefield Bangalore, Karnataka 560066 India EMail: mahendrasingh@huawei.com