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Versions: 00 01 02 03 04                                                
IDR Working Group                                                J. Zhou
Internet-Draft                                             Chunning. Dai
Intended status: Standards Track                            Shaofu. Peng
Expires: July 3, 2020                                          ZTE Corp.
                                                            Dec 31, 2019


                Inter-domain Network Slicing via BGP-LU
                   draft-zhou-idr-inter-domain-lcu-00

Abstract

   This document aims to solve inter-domain network slicing problems
   using existing technologies.  It attempts to establish multiple BGP-
   LU LSPs of different colors for a prefix to stitch multiple network
   segments.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on July 3, 2020.

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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   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements notation . . . . . . . . . . . . . . . . . . . .   2
   3.  Color . . . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   4.  Advertising multiple paths  . . . . . . . . . . . . . . . . .   3
   5.  Generating Labels by Path . . . . . . . . . . . . . . . . . .   4
   6.  Deploy Considerations . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   As described in [I-D.peng-teas-network-slicing], in the traditional
   end to end inter-domain network slicing, BGP-LU is used as a
   distributed slicing scheme.  [RFC8277] specifies a set of procedures
   for using BGP to advertise that a specified router has bound a
   specified MPLS label to a specified address prefix.  It's an
   effective way for inter-domain labels, but it does not have the
   ability to select the underlying network resources.

   This document describes the colored BGP-LU LSP, in which the routing
   prefix not only carries a label(or a sequence of labels), but also
   carries an unique color attribute which helps to select the
   underlying logic slice.

   [RFC7911] defines a BGP extension that allows the advertisement of
   multiple paths of the same address prefix.  It can help with optimal
   routing and in a network by providing potential alternate or backup
   paths.  In this document, it is not used for the link backup.  It is
   only used to advertise multiple paths, whether intra-domain or inter-
   domain.

2.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  Color

   [I-D.ietf-idr-tunnel-encaps] introduces the concept of color, which
   is used as one of the KEY of SR policy
   [I-D.ietf-spring-segment-routing-policy].  The color of SR policy




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   defines a TE purpose, which includes a set of constraints such as
   bandwidth, delay, TE metric, etc.

   Color is used a policy keyword to help routing decisions and can be
   carried through Community attribute [I-D.ietf-idr-tunnel-encaps] in
   BGP.  Each UPDATE SHOULD contain a Color Extended Community with a
   specific color value, the Color Sub-TLV is only an opaque extended
   community.

4.  Advertising multiple paths

   Consider the following LSR topology in Figure 1: PE1---ASBR1---ASBR2
   ---PE2.  Packet transfers from PE2 to PE1.  The overlay service of
   PE1 to PE2 has two colors, color1 and color2.


            .----.                                      .------.
           (      )                                    (        )
        .-(        )-.                              .-(          )-.
   +---+---color1----+----+                     +---+----color1----+---+
   |PE1|\---SR-TE1---/|AS |-sub-if1 with slice1-|AS |\---SR-TE1---/|PE2|
   |   |/---SR-TE2---\|BR1|-sub-if2 with slice2-|BR2|/---SR-TE2---\|   |
   +---+---color2---- +---+                     +---+--color2------+---+
       (              )                             (              )
         '--( AS1 )--'                                '--( AS2 )--'
             (   )                                        (   )
              '-'                                          '-'

                 Figure 1: Network Slicing Example

   According to the extended NLRI Encodings in [RFC7911], in order to
   advertise multiple paths for the same address prefix, PE1 MUST encode
   two different NLRIs to advertise the two paths.  Every NLRI has a
   unique Path Identifier.

                     +--------------------------------+
                     | Path Identifier (4 octets)     |
                     +--------------------------------+
                     | Length (1 octet)               |
                     +--------------------------------+
                     | Prefix (variable)              |
                     +--------------------------------+

   The Path Identifier only identifies a path, not carrying any
   particular semantics.  It MAY be generated from the two-tuple
   <Prefix,Color>. Also, it MAY be generated from the information
   containing Prefix and Color.




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   Finally, There are two BGP UPDATE NLRIs from PE1 to ASBR1, <prefix,
   pathid1> with color1 extended community and <prefix, pathid2> with
   color2 extended community.  Pathid1 and pathid2 in two UPDATE NLRI
   MUST be different.  As described in [RFC8277], they have the same
   label value, however, different label value is also possible.

5.  Generating Labels by Path

   To realize the inter-domain multiple paths, the border routers of per
   domain SHOULD consider the diversity of paths when generating the
   labels.


   <1.1.1.1, path-id1>     <1.1.1.1, path-id1>    <1.1.1.1, path-id1>
   <color1, label200>      <color1, label201>     <color1, label201>
   ------------------------------------------------------------------>
            .----.                                      .------.
           (      )                                    (        )
        .-(        )-.                              .-(          )-.
   +---+---color1----+----+                     +---+----color1----+---+
   |PE1|\---SR-TE1---/|AS |-sub-if1 with slice1-|AS |\---SR-TE1---/|PE2|
   |   |/---SR-TE2---\|BR1|-sub-if2 with slice2-|BR2|/---SR-TE2---\|   |
   +---+---color2---- +---+                     +---+--color2------+---+
       (              )                             (              )
         '--( AS1 )--'                                '--( AS2 )--'
             (   )                                        (   )
              '-'                                          '-'
   ------------------------------------------------------------------->
   <1.1.1.1, path-id2>     <1.1.1.1, path-id2>      <1.1.1.1, path-id2>
   <color2, label200>      <color2, label202>       <color2, label202>

     Label Exchange Tables:
     ASBR1:                          ASBR2:
     inLabel outLabel nextHop        inLabel outLabel nextHop
     201      200     SR-TE1         201      201     sub-if1
     202      200     SR-TE2         202      202     sub-if2

     PE2:
     prefix   color  outLabel   nextHop
     1.1.1.1    1       201      SR-TE1
     1.1.1.1    2       202      SR-TE2

         Figure 2: Details of Network Slicing Example

   Suppose ASBR1 receives two paths from PE1, with next hop 1.1.1.1,
   path identifier 1 and 2, ASBR1 MUST modify the next hop to itself,
   and generate two new labels based on two paths.  As depicted in
   Figure 2, <1.1.1.1, color1> generates label 201, <1.1.1.1, color2>



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   generates label 202.  Both of them are the local label exchange table
   items.  Similarly, ASBR2 also generates two different labels based on
   the two paths.  As shown in Figure 2, multiple end to end BGP-LU LSP
   are established.

   So, at the entry node of per domain, BGP-LU LSP generated for
   specific color is over intra-domain SR-TE or SR Best-effort path
   generated for the color again.  At exit node of per domain, BGP-LU
   LSP generated for specific color selects inter-domain forwarding
   resource per color.

6.  Deploy Considerations

   o  The premise of this document is that all border routers SHOULD
      have the same understanding of a color value.  For example, PE1
      understands color1 representing a low packet loss rate, and ASBR1
      must think so and apply it to the local forwarding policy.

   o  All BGP routers(PE1--ASBR1, ASBR1---ASBR2, ASBR2---PE2) SHOULD be
      BGP-LU neighbors in advance.

   o  All routers require the ADD-PATH Capability which is described in
      chapter 4 of [RFC7911].

   o  If any Router Reflector existed in the network, it SHOULD support
      this function.  Later will discuss Confederation.

7.  Security Considerations

   TBD

8.  References

8.1.  Normative References

   [I-D.ietf-idr-tunnel-encaps]
              Patel, K., Velde, G., and S. Ramachandra, "The BGP Tunnel
              Encapsulation Attribute", draft-ietf-idr-tunnel-encaps-15
              (work in progress), December 2019.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-06 (work in progress),
              December 2019.






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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7911]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", RFC 7911,
              DOI 10.17487/RFC7911, July 2016,
              <https://www.rfc-editor.org/info/rfc7911>.

   [RFC8277]  Rosen, E., "Using BGP to Bind MPLS Labels to Address
              Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
              <https://www.rfc-editor.org/info/rfc8277>.

8.2.  Informative References

   [I-D.peng-teas-network-slicing]
              Peng, S., Chen, R., Mirsky, G., and F. Qin, "Packet
              Network Slicing using Segment Routing", draft-peng-teas-
              network-slicing-02 (work in progress), December 2019.

Authors' Addresses

   Jin Zhou
   ZTE Corp.

   Email: zhou.jin6@zte.com.cn


   Chunning Dai
   ZTE Corp.

   Email: dai.chunning@zte.com.cn


   Shaofu Peng
   ZTE Corp.

   Email: peng.shaofu@zte.com.cn












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