Segment Routing with the MPLS Data Plane
RFC 8660
Internet Engineering Task Force (IETF) A. Bashandy, Ed.
Request for Comments: 8660 Arrcus
Category: Standards Track C. Filsfils, Ed.
ISSN: 2070-1721 S. Previdi
Cisco Systems, Inc.
B. Decraene
S. Litkowski
Orange
R. Shakir
Google
December 2019
Segment Routing with the MPLS Data Plane
Abstract
Segment Routing (SR) leverages the source-routing paradigm. A node
steers a packet through a controlled set of instructions, called
segments, by prepending the packet with an SR header. In the MPLS
data plane, the SR header is instantiated through a label stack.
This document specifies the forwarding behavior to allow
instantiating SR over the MPLS data plane (SR-MPLS).
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8660.
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
1.1. Requirements Language
2. MPLS Instantiation of Segment Routing
2.1. Multiple Forwarding Behaviors for the Same Prefix
2.2. SID Representation in the MPLS Forwarding Plane
2.3. Segment Routing Global Block and Local Block
2.4. Mapping a SID Index to an MPLS Label
2.5. Incoming Label Collision
2.5.1. Tiebreaking Rules
2.5.2. Redistribution between Routing Protocol Instances
2.6. Effect of Incoming Label Collision on Outgoing Label
Programming
2.7. PUSH, CONTINUE, and NEXT
2.7.1. PUSH
2.7.2. CONTINUE
2.7.3. NEXT
2.8. MPLS Label Downloaded to the FIB for Global and Local SIDs
2.9. Active Segment
2.10. Forwarding Behavior for Global SIDs
2.10.1. Forwarding for PUSH and CONTINUE of Global SIDs
2.10.2. Forwarding for the NEXT Operation for Global SIDs
2.11. Forwarding Behavior for Local SIDs
2.11.1. Forwarding for the PUSH Operation on Local SIDs
2.11.2. Forwarding for the CONTINUE Operation for Local SIDs
2.11.3. Outgoing Label for the NEXT Operation for Local SIDs
3. IANA Considerations
4. Manageability Considerations
5. Security Considerations
6. References
6.1. Normative References
6.2. Informative References
Appendix A. Examples
A.1. IGP Segment Examples
A.2. Incoming Label Collision Examples
A.2.1. Example 1
A.2.2. Example 2
A.2.3. Example 3
A.2.4. Example 4
A.2.5. Example 5
A.2.6. Example 6
A.2.7. Example 7
A.2.8. Example 8
A.2.9. Example 9
A.2.10. Example 10
A.2.11. Example 11
A.2.12. Example 12
A.2.13. Example 13
A.2.14. Example 14
A.3. Examples for the Effect of Incoming Label Collision on an
Outgoing Label
A.3.1. Example 1
A.3.2. Example 2
Acknowledgements
Contributors
Authors' Addresses
1. Introduction
The Segment Routing architecture [RFC8402] can be directly applied to
the MPLS architecture with no change in the MPLS forwarding plane.
This document specifies forwarding-plane behavior to allow Segment
Routing to operate on top of the MPLS data plane (SR-MPLS). This
document does not address control-plane behavior. Control-plane
behavior is specified in other documents such as [RFC8665],
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