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SPRING                                                       C. Weiqiang
Internet-Draft                                              China Mobile
Intended status: Informational                                 G. Mirsky
Expires: September 7, 2020                                     ZTE Corp.
                                                                L. Aihua
                                                               P. Shaofu
                                                         ZTE Corporation
                                                           March 6, 2020


           SRv6 network programming using Unified Identifier
         draft-mirsky-spring-unified-id-network-programming-00

Abstract

   This draft describes how Unified Segment Identifier can be used to
   achieve the goals of SRv6 network programming.

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 September 7, 2020.

Copyright Notice

   Copyright (c) 2020 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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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions used in this document . . . . . . . . . . . .   2
       1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   3
       1.1.2.  Requirements Language . . . . . . . . . . . . . . . .   3
   2.  SRv6 Network Programming using U-SID  . . . . . . . . . . . .   3
     2.1.  SRv6 Network Programming  . . . . . . . . . . . . . . . .   3
     2.2.  SRv6 Network Programming Using 32bit U-SID  . . . . . . .   4
     2.3.  U-SID with MPLS Programming Process . . . . . . . . . . .   5
       2.3.1.  U-SID with MPLS Support Programming using Flavors . .   5
     2.4.  U-SID with SRv6 Programming process . . . . . . . . . . .   6
     2.5.  U-SID Complementary Method  . . . . . . . . . . . . . . .   6
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Segment Routing architecture [RFC8402] leverages the paradigm of
   source routing.  It can be realized in a network data plane by
   prepending the packet with a list of instructions, a.k.a.  Segment
   Identifiers (SIDs).  A segment can be encoded as a Multi-Protocol
   Label Switching (MPLS) label, IPv4 address, or IPv6 address.  Segment
   Routing can be applied in MPLS data plane by encoding 20-bits SIDs in
   MPLS label stack [RFC8660].  It also can be applied to IPv6 data
   plane by encoding a list of 128-bits SIDs in IPv6 Segment Routing
   Extension Header (SRH) [I-D.ietf-6man-segment-routing-header].

   Unified SID [I-D.mirsky-6man-unified-id-sr] defines an extension of
   SRH that enables the use of a shorter segment identifier, such as
   32-bits Label format SID or 32-bits IP address format SID.

   SRv6 network programming is defined
   [I-D.ietf-spring-srv6-network-programming].  SRv6 network programming
   can be supported using Unified SID.

1.1.  Conventions used in this document








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1.1.1.  Terminology

   SR: Segment Routing

   SRH: Segment Routing Extension Header

   MPLS: Multiprotocol Label Switching

   SR-MPLS: Segment Routing using MPLS data plane

   SID: Segment Identifier

   IGP: Interior Gateway Protocol

   DA: Destination Address

   SRv6: Segment Routing in IPv6

   U-SID: Unified Segment Identifier

1.1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  SRv6 Network Programming using U-SID

2.1.  SRv6 Network Programming

   [I-D.ietf-spring-srv6-network-programming] defines an SRv6 SID as
   consisting of LOC:FUNCT:ARG, where a locator (LOC) is encoded in the
   L most significant bits of the SID, followed by F bits of function
   (FUNCT) and A bits of arguments (ARG).  L, the length of the locator,
   is flexible, and an operator is free to use the locator length of
   their choice.  F and A may be any value as long as L + F + A <= 128.
   When L + F + A is less than 128, then the remainder of the SID MUST
   be zero.

   A locator may be represented as B:N where B is the SRv6 SID block
   (IPv6 subnet allocated for SRv6 SIDs by the operator) and N is the
   identifier of the parent node instantiating the SID.  The FUNCT is an
   opaque identification of a local behavior bound to the SID.  An SRv6
   endpoint behavior MAY require additional information for its
   processing (e.g., related to the flow or service).  This information
   MAY be encoded in the ARG bits of the SID.



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2.2.  SRv6 Network Programming Using 32bit U-SID

   [I-D.mirsky-6man-unified-id-sr] defines a 32 bits SID as an MPLS
   label or an IPv4 address or a complementary SID to a common IPv4/IPv6
   prefix.  If the U-SID represents an MPLS label, it could be mapped to
   the 128-bits SRv6 SID.  And if this U-SID represents a complementary
   U-SID to a common IPv6 prefix, it could be associated with an SRv6
   SID (a method to establish such association could use mapping,
   stitching, shifting, or translation).  This SID can be compliant to
   the programming SID format as LOC:FUNCT:ARG, this means complementing
   the SRv6 SID of programming format to 32-bits U-SID.  A U-SID with
   MPLS label format can support network programming, as illustrated in
   Figure 1:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           U-LOC (20bit, Label)        |P|U|D|R|U-FUNCT (U-ARG)|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                               |    Context (12bit)    |
                                               +-----------------------+


    Figure 1: Example of U-SID supporting Network Programming with SR-
                                   MPLS

   The context field can be defined as follow:

      P-Flag: PSP (Penultimate Segment Pop of the SRH) Flag.  If set,
      then the penultimate segment node MUST remove the SRH from the
      IPv6 extension header chain.

      U-Flag: USP (Ultimate Segment Pop of the SRH) Flag.  If set, then
      the ultimate segment node MUST remove the SRH from the IPv6
      extension header chain and proceed to process the next header in
      the packet.

      D-Flag: USD (Ultimate Segment Decapsulation) Flag.  If set, then
      the ultimate segment node MUST skip the SRH processing and proceed
      to the next header.

      R-Flag: Reserved Flag.

      Function: 8-bits to store the short KEY for the specific table
      lookup.  The MPLS label in the leftmost 20-bits will identify the
      context-specific table.  For the context table that has a longer
      KEY than 8-bits, the next 32-bits SID could be used for this
      purpose.



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   A format of U-SID as 32-bits IP address can support network
   programming, as illustrated in Figure 2.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             U-LOC             |        U-FUNCT (U-ARG)        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    Figure 2: Example of U-SID supporting Network Programming with SRv6

   In this case, U-SID is split to 16-bits locator (U-LOC) and 16-bits
   function (U-FUNCT, U-ARG is optional).  The operator can use any
   method to compress the 128-bits SRv6 SID to 32-bits complementary
   U-SID, such as mapping, stitching, shifting or translation, etc.  For
   example, an operator can simply compress the original locator to a
   shorter locator.  If the original SRv6 locator consists of B:N, this
   case the N is 16-bits.  So, only the N is the U-LOC of U-SID and the
   B can be advertised by IGP protocol in the domain.  the length of
   U-LOC and U-FUNCT (U-ARG) is flexible, and an operator is free to use
   the length of their choice.  The length of U-LOC and U-FUNCT (U-ARG)
   may be any value as long as its sum mo more than 32.  The compressing
   and the advertising method are out of the scope of this draft.

2.3.  U-SID with MPLS Programming Process

2.3.1.  U-SID with MPLS Support Programming using Flavors

   [I-D.ietf-spring-srv6-network-programming] introduced the PSP, USP,
   and USD flavors for SRv6 SID.  The U-FUNCT (U-ARG) and Flavors are
   combined to allocate different SRv6 SIDs, or someone can understand
   that each U-FUNCT (U-ARG) codepoint itself has a determined flavor.
   That is no problem for SRv6 SID allocation because IPv6 address
   resource is enough.  For SR-MPLS over SRH in this document, a
   different MPLS label is used for each topology type of SID, such as
   node SID, adjacency SID, or service type of SID, etc.  All these
   types of SIDs are equivalent to SIDs defined in SRv6.  The label
   allocation is independent of flavors.  For the use of the behavior
   flavor, an explicit standard Flavor codepoint could be set on the
   rightmost 12-bits of the SID entry (label) in SRH.

   The codepoint can be used as U-FUNCT (U-ARG) to support the network
   programming.  In this case, a 20-bits MPLS label of U-SID is
   interpreted as the U-LOC.  The U-FUNCT in the codepoint field of
   U-SID can be advertised by the control plane.





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   Note that the flavor codepoint is different from the PHP flag of
   prefix-SID in SR-MPLS.

2.4.  U-SID with SRv6 Programming process

   Processing of SRH with elements carrying 32 bits-long SIDs closely
   follows SRH processing as defined in Section 4.3.1.1
   [I-D.ietf-6man-segment-routing-header] and the "End" behavior is
   demonstrated in the pseudo-code below, but it equally applies to all
   SID behaviors.  When N with U-SID receives a packet whose IPv6 DA is
   S and S is a local End SID.  The lines S08 and S14 of the End
   processing which was, as per Section 4.1 of
   [I-D.ietf-spring-srv6-network-programming]:

   S08.    max_LE = ( Hdr Ext Len * 8/ sizeof(SRH_element) ) - 1
           [...]
   S14.    Get 128-bits IPv6 DA by 32-bits U-SID
                   from Segment List[Segments Left]
           Update IPv6 DA

   Note: S14. Obtaining 128-bits IPv6 DA from complementary U-SID
     can be done by mapping, stitching, shifting, translation, etc.


2.5.  U-SID Complementary Method

   The 32-bits U-SID MAY be used as complementary to a common IPv6
   prefix to construct an IPv6 address SID (SRv6 SID).  Many methods can
   be used to achieve that, including mapping, stitching, shifting,
   translation, etc.

   Generally speaking, the relationship between 32-bits U-SID and
   128-bits SRv6 SID can be established using any transformation
   function as long as the relationship unambiguous and reversible,
   i.e., there exists a transformation function that when being applied
   to the result produces the original value.  We can use a function F
   as a method that produces 32-bits U-SID from 128-bits SRv6 SID.  Then
   there must be a function F', used as the reversible method, to
   produce the original 128-bits SRv6 SID from the 32-bits U-SID.  These
   functions are illustrated below:

   U-SID = F (SRv6 SID);
   SRv6 SID = F' (U-SID);


   The details of these functions will be demonstrated in the future.





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3.  IANA Considerations

   This draft has no requests for IANA actions.  This section can be
   removed before the publication.

4.  Security Considerations

   TBD

5.  Acknowledgements

   TBD

6.  Normative References

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-26 (work in
              progress), October 2019.

   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-12 (work in
              progress), March 2020.

   [I-D.mirsky-6man-unified-id-sr]
              Cheng, W., Mirsky, G., Peng, S., Aihua, L., Wan, X., Wei,
              C., and S. Shay, "Unified Identifier in IPv6 Segment
              Routing Networks", draft-mirsky-6man-unified-id-sr-05
              (work in progress), February 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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.





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   [RFC8660]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing with the MPLS Data Plane", RFC 8660,
              DOI 10.17487/RFC8660, December 2019,
              <https://www.rfc-editor.org/info/rfc8660>.

Authors' Addresses

   Cheng Weiqiang
   China Mobile
   Beijing
   China

   Email: chengweiqiang@chinamobile.com


   Greg Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com


   Liu Aihua
   ZTE Corporation
   Zhongxing Industrial Park, Nanshan District
   Shenzhen
   China

   Email: liu.aihua@zte.com.cn


   Peng Shaofu
   ZTE Corporation
   No.50 Software Avenue, Yuhuatai District
   Nanjing
   China

   Email: peng.shaofu@zte.com.cn













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