An MPLS-Based Forwarding Plane for Service Function Chaining
RFC 8595

Document Type RFC - Proposed Standard (June 2019; No errata)
Last updated 2019-06-07
Replaces draft-farrel-mpls-sfc
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IESG IESG state RFC 8595 (Proposed Standard)
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Send notices to Loa Andersson <loa@pi.nu>
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Internet Engineering Task Force (IETF)                         A. Farrel
Request for Comments: 8595                            Old Dog Consulting
Category: Standards Track                                      S. Bryant
ISSN: 2070-1721                                                Futurewei
                                                                J. Drake
                                                        Juniper Networks
                                                               June 2019

      An MPLS-Based Forwarding Plane for Service Function Chaining

Abstract

   This document describes how Service Function Chaining (SFC) can be
   achieved in an MPLS network by means of a logical representation of
   the Network Service Header (NSH) in an MPLS label stack.  That is,
   the NSH is not used, but the fields of the NSH are mapped to fields
   in the MPLS label stack.  This approach does not deprecate or replace
   the NSH, but it acknowledges that there may be a need for an interim
   deployment of SFC functionality in brownfield networks.

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/rfc8595.

Farrel, et al.               Standards Track                    [Page 1]
RFC 8595                        MPLS SFC                       June 2019

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 ....................................................3
   2. Requirements Language ...........................................4
   3. Choice of Data-Plane SPI/SI Representation ......................4
   4. Use Case Scenarios ..............................................5
      4.1. Label Swapping for Logical NSH .............................5
      4.2. Hierarchical Encapsulation .................................5
      4.3. Fine Control of Service Function Instances .................6
      4.4. Micro Chains and Label Stacking ............................6
      4.5. SFC and Segment Routing ....................................6
   5. Basic Unit of Representation ....................................6
   6. MPLS Label Swapping .............................................7
   7. MPLS Label Stacking ............................................10
   8. Mixed-Mode Forwarding ..........................................12
   9. A Note on Service Function Capabilities and SFC Proxies ........13
   10. Control-Plane Considerations ..................................14
   11. Use of the Entropy Label ......................................14
   12. Metadata ......................................................15
      12.1. Indicating Metadata in User Data Packets .................16
      12.2. In-Band Programming of Metadata ..........................18
           12.2.1. Loss of In-Band Metadata ..........................21
   13. Worked Examples ...............................................22
   14. Implementation Notes ..........................................26
   15. Security Considerations .......................................26
   16. IANA Considerations ...........................................28
   17. References ....................................................29
      17.1. Normative References .....................................29
      17.2. Informative References ...................................30
   Acknowledgements ..................................................31
   Contributors ......................................................31
   Authors' Addresses ................................................32

Farrel, et al.               Standards Track                    [Page 2]
RFC 8595                        MPLS SFC                       June 2019

1.  Introduction

   Service Function Chaining (SFC) is the process of directing packets
   through a network so that they can be acted on by an ordered set of
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