Carrying SID Algorithm information in PCE-based Networks.
draft-tokar-pce-sid-algo-00

Abstract

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.

Copyright Notice

Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. SR ERO NAI Extensions
• 4. Operation
• 5. Security Considerations
• 6. IANA Considerations
• 6.1. PCEP SR-ERO NAI Types
• 7. Normative References
• Authors' Addresses

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:

ERO:

Explicit Route Object

IGP:

Interior Gateway Protocol

NAI:

Node or Adjacency Identifier.

PCE:

Path Computation Element

PCEP:

Path Computation Element Protocol.

SID:

Segment Identifier.

SR:

Segment Routing.

SR-TE:

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:

• NT=TBD1: The NAI is an IPv4 node ID with Algorithm.
• NT=TBD1: The NAI is an IPv6 node ID 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 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.

7. Normative References

Authors' Addresses