BGP Prefix Segment in Large-Scale Data Centers
RFC 8670

Document Type RFC - Informational (December 2019; No errata)
Authors Clarence Filsfils  , Stefano Previdi  , Gaurav Dawra  , Ebben Aries  , Petr Lapukhov 
Last updated 2019-12-06
Replaces draft-filsfils-spring-segment-routing-msdc
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Internet Engineering Task Force (IETF)                  C. Filsfils, Ed.
Request for Comments: 8670                                    S. Previdi
Category: Informational                              Cisco Systems, Inc.
ISSN: 2070-1721                                                 G. Dawra
                                                                E. Aries
                                                            Arrcus, Inc.
                                                             P. Lapukhov
                                                           December 2019

             BGP Prefix Segment in Large-Scale Data Centers


   This document describes the motivation for, and benefits of, applying
   Segment Routing (SR) in BGP-based large-scale data centers.  It
   describes the design to deploy SR in those data centers for both the
   MPLS and IPv6 data planes.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see 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

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
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   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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
   2.  Large-Scale Data-Center Network Design Summary
     2.1.  Reference Design
   3.  Some Open Problems in Large Data-Center Networks
   4.  Applying Segment Routing in the DC with MPLS Data Plane
     4.1.  BGP Prefix Segment (BGP Prefix-SID)
     4.2.  EBGP Labeled Unicast (RFC 8277)
       4.2.1.  Control Plane
       4.2.2.  Data Plane
       4.2.3.  Network Design Variation
       4.2.4.  Global BGP Prefix Segment through the Fabric
       4.2.5.  Incremental Deployments
     4.3.  IBGP Labeled Unicast (RFC 8277)
   5.  Applying Segment Routing in the DC with IPv6 Data Plane
   6.  Communicating Path Information to the Host
   7.  Additional Benefits
     7.1.  MPLS Data Plane with Operational Simplicity
     7.2.  Minimizing the FIB Table
     7.3.  Egress Peer Engineering
     7.4.  Anycast
   8.  Preferred SRGB Allocation
   9.  IANA Considerations
   10. Manageability Considerations
   11. Security Considerations
   12. References
     12.1.  Normative References
     12.2.  Informative References
   Authors' Addresses

1.  Introduction

   Segment Routing (SR), as described in [RFC8402], leverages the
   source-routing paradigm.  A node steers a packet through an ordered
   list of instructions called "segments".  A segment can represent any
   instruction, topological or service based.  A segment can have a
   local semantic to an SR node or a global semantic within an SR
   domain.  SR allows the enforcement of a flow through any topological
   path while maintaining per-flow state only from the ingress node to
   the SR domain.  SR can be applied to the MPLS and IPv6 data planes.

   The use cases described in this document should be considered in the
   context of the BGP-based large-scale data-center (DC) design
   described in [RFC7938].  This document extends it by applying SR both
   with IPv6 and MPLS data planes.

2.  Large-Scale Data-Center Network Design Summary

   This section provides a brief summary of the Informational RFC
   [RFC7938], which outlines a practical network design suitable for
   data centers of various scales:

   *  Data-center networks have highly symmetric topologies with
      multiple parallel paths between two server-attachment points.  The
      well-known Clos topology is most popular among the operators (as
      described in [RFC7938]).  In a Clos topology, the minimum number
      of parallel paths between two elements is determined by the
      "width" of the "Tier-1" stage.  See Figure 1 for an illustration
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