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Versions: 00 01 02                                                      
IDR Working Group                                                R. Chen
Internet-Draft                                                   Ch. Dai
Intended status: Standards Track                                Sh. Peng
Expires: July 14, 2021                                   ZTE Corporation
                                                        January 10, 2021


                Inter-domain Network Slicing via BGP-LU
                   draft-zhou-idr-inter-domain-lcu-02

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
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   This Internet-Draft will expire on July 14, 2021.

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   Copyright (c) 2021 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements notation . . . . . . . . . . . . . . . . . . . .   2
   3.  Color . . . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   4.  Advertising multiple paths  . . . . . . . . . . . . . . . . .   3
   5.  Assigning Label(s)  . . . . . . . . . . . . . . . . . . . . .   3
   6.  Inter-domain Network Slicing via BGP-LU . . . . . . . . . . .   4
   7.  Deploy Considerations . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Information References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   As described in [I-D.peng-teas-network-slicing], in the traditional
   end to end inter-domain network slicing, BGP-LU to build inter-domain
   MPLS LSP, and overlay service will be directly over BGP-LU LSP.

   [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, which defines the
   multiple paths for the same destination prefix can be advertised in
   BGP UPDATE message, and each UPDATE message can contain the color
   Extended Community [I-D.ietf-idr-tunnel-encaps] with different color
   value, which helps to select the underlying resources.

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




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   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

   A BGP speaker can advertise multiple paths for a particular address
   prefix by a Path identifier in the Extended NLRI Encoding as defined
   in [RFC7911].

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

   The Path Identifier only identifies a path, not carrying any
   particular semantics.In this document, it can be generated by the
   <Prefix,Color> tuple.  The assignment to the Path Identifier for a
   path by a BGP speaker is purely a local matter.

   Therefore, if a BGP speaker has two colors for the prefix P, which
   correspond to two different paths, it may advertise two UPDATE NLRIs,
   <prefix, pathid1> with color1 extended community and <prefix,
   pathid2> with color2 extended community.  Pathid1 and pathid2 in two
   UPDATE NLRIs MUST be different.

   Note that in this document, BGP speakers acting as border routers
   that interact with external neighbors need to support advertising
   multiple paths corresponding to the same prefix.  Although multiple
   paths have differnet path ids, they have the same next hop.  As for
   the procedures of mutual backup paths with the same prefix and the
   differnet next hops, refer to [RFC7911].

5.  Assigning Label(s)

   [RFC8277] describes how to use BGP to bind MPLS label(s) to address
   prefixes.  The specific format of the UPDATE message is detailed in
   Section 2 of [RFC8277].

   [RFC8277] Section 3.2 details the process of modifying the Label
   field during propagation.  When propagating a SAFI-4 or SAFI-128
   route, if the Network Address of Next Hop field has never changed,
   the label field must remain unchanged.  Otherwise, if the Network



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   Address of Next Hop field is changed, the label field(s) of the
   propagating route must contain the label(s) that is (are) bound to
   the prefix at the new next hop.  What the label changes to depends on
   the local policy.  However, LSPs with different color paths need to
   have different label(s).

6.  Inter-domain Network Slicing via BGP-LU

   [RFC7911] defined that multiple paths for a particular address prefix
   by a Path identifier can be advertised in BGP UPDATE message, and
   each UPDATE message can contain the Color Extended Community
   [I-D.ietf-idr-tunnel-encaps] with different color value.  That is a
   simple existing way to realize BGP-LU color function, and no protocol
   extension required.

   Consider the following example of establishing multiple BGP-LU LSPs
   per different colors in a cross-domain scenario.


































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   <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 1: Example of Inter-domain Network Slicing via BGP-LU

   In figure 1, PE1 advertises two paths: <1.1.1.1, path-id1> carries
   the color1 attribute and <1.1.1.1, path-id2> carries the color2
   attribute to ASBR1.PE1 advertises the binding between the prefix
   1.1.1.1 and label 200.  Because of the end node, both paths have the
   same label value 200.

   ASBR1 receives these two paths from PE1, and when sending to ASBR2,
   it modifies the next hop to itself.  And allocate two new labels
   based on <prefix, path-id, color>.  As shown in Figure 1, ASBR1 sends
   two paths to ASBR2, <1.1.1.1, path-id1> carries color1+label201, and
   <1.1.1.1, path-id2> carries color2+label202.

   Similarly, ASBR2 also generates two different labels based on the
   <prefix, path-id, color>.  As shown in Figure 1, multiple end to end
   BGP-LU LSPs are established.Different BGP-LU LSPs select the lower
   SR-BE/TE tunnels according to their colors.




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7.  Deploy Considerations

   All BGP routers (PE1--ASBR1, ASBR1---ASBR2, ASBR2---PE2) SHOULD be
   BGP-LU neighbors in advance.  There may be multiple border routers to
   ensure multipath backup.  All routers require the ADD-PATH Capability
   which is described in chapter 4 of [RFC7911].

   This document not only supports interprovider VPNs while the customer
   sites belong to different ASs, but also supports the Carrier-of-
   Carriers VPNs while the customer site belong to the same AS.
   Multiple operators are involved, so AS border routers may involve
   color mapping, color namespaces, or color service chains.  These
   services can be delivered by the controller configurations or the
   local configurations.

8.  Security Considerations

   TBD

9.  IANA Considerations

   TBD.

10.  References

10.1.  Normative References

   [I-D.ietf-idr-tunnel-encaps]
              Patel, K., Velde, G., Sangli, S., and J. Scudder, "The BGP
              Tunnel Encapsulation Attribute", draft-ietf-idr-tunnel-
              encaps-22 (work in progress), January 2021.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-09 (work in progress),
              November 2020.

   [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>.




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   [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>.

10.2.  Information 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-04 (work in progress), October 2020.

Authors' Addresses

   Ran Chen
   ZTE Corporation

   Email: chen.ran@zte.com.cn


   Chunning Dai
   ZTE Corporation

   Email: dai.chunning@zte.com.cn


   Shaofu Peng
   ZTE Corporation

   Email: peng.shaofu@zte.com.cn






















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