MPLS Segment Routing over IP
RFC 8663

Document Type RFC - Proposed Standard (December 2019; No errata)
Last updated 2019-12-06
Replaces draft-xu-mpls-sr-over-ip
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Stream WG state Submitted to IESG for Publication
Document shepherd Loa Andersson
Shepherd write-up Show (last changed 2019-01-09)
IESG IESG state RFC 8663 (Proposed Standard)
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Send notices to Loa Andersson <loa@pi.nu>
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Internet Engineering Task Force (IETF)                             X. Xu
Request for Comments: 8663                                  Alibaba, Inc
Category: Standards Track                                      S. Bryant
ISSN: 2070-1721                                   Futurewei Technologies
                                                               A. Farrel
                                                      Old Dog Consulting
                                                               S. Hassan
                                                                   Cisco
                                                           W. Henderickx
                                                                   Nokia
                                                                   Z. Li
                                                                  Huawei
                                                           December 2019

                      MPLS Segment Routing over IP

Abstract

   MPLS Segment Routing (SR-MPLS) is a method of source routing a packet
   through an MPLS data plane by imposing a stack of MPLS labels on the
   packet to specify the path together with any packet-specific
   instructions to be executed on it.  SR-MPLS can be leveraged to
   realize a source-routing mechanism across MPLS, IPv4, and IPv6 data
   planes by using an MPLS label stack as a source-routing instruction
   set while making no changes to SR-MPLS specifications and
   interworking with SR-MPLS implementations.

   This document describes how SR-MPLS-capable routers and IP-only
   routers can seamlessly coexist and interoperate through the use of
   SR-MPLS label stacks and IP encapsulation/tunneling such as MPLS-
   over-UDP as defined in RFC 7510.

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/rfc8663.

Copyright Notice

   Copyright (c) 2019 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   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
     1.1.  Terminology
   2.  Use Cases
   3.  Procedures of SR-MPLS-over-IP
     3.1.  Forwarding Entry Construction
       3.1.1.  FIB Construction Example
     3.2.  Packet-Forwarding Procedures
       3.2.1.  Packet Forwarding with Penultimate Hop Popping
       3.2.2.  Packet Forwarding without Penultimate Hop Popping
       3.2.3.  Additional Forwarding Procedures
   4.  IANA Considerations
   5.  Security Considerations
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   MPLS Segment Routing (SR-MPLS) [RFC8660] is a method of source
   routing a packet through an MPLS data plane.  This is achieved by the
   sender imposing a stack of MPLS labels that partially or completely
   specify the path that the packet is to take and any instructions to
   be executed on the packet as it passes through the network.  SR-MPLS
   uses an MPLS label stack to encode a sequence of source-routing
   instructions.  This can be used to realize a source-routing mechanism
   that can operate across MPLS, IPv4, and IPv6 data planes.  This
   approach makes no changes to SR-MPLS specifications and allows
   interworking with SR-MPLS implementations.  More specifically, the
   source-routing instructions in a source-routed packet could be
   uniformly encoded as an MPLS label stack regardless of whether the
   underlay is IPv4, IPv6 (including Segment Routing for IPv6 (SRv6)
   [RFC8354]), or MPLS.

   This document describes how SR-MPLS-capable routers and IP-only
   routers can seamlessly coexist and interoperate through the use of
   SR-MPLS label stacks and IP encapsulation/tunneling such as MPLS-
   over-UDP [RFC7510].

   Section 2 describes various use cases for tunneling SR-MPLS over IP.
   Section 3 describes a typical application scenario and how the packet
   forwarding happens.
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