MPLS Segment Routing over IP
RFC 8663
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
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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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