[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Nits]

Versions: 00

SPRING Working Group                                            Yao. Liu
Internet-Draft                                           ZTE Corporation
Intended status: Standards Track                           March 1, 2020
Expires: September 2, 2020


           Metadata in SR Service Programming Considerations
                  draft-liu-spring-sr-sfc-metadata-00

Abstract

   This document discusses different ways to carry metadata in SR
   service programming data plane.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 2, 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
   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.






Liu                     Expires September 2, 2020               [Page 1]


Internet-Draft            SR based SFC Metadata               March 2020


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Metadata in SRV6 Data Plane . . . . . . . . . . . . . . . . .   2
   3.  Metadata in SR-MPLS Data Plane  . . . . . . . . . . . . . . .   2
     3.1.  Indicating Metadata in User Data Packets  . . . . . . . .   3
     3.2.  Per Packet Metadata . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Service Function Chaining (SFC)[7665] provides support for the
   creation of composite services that consist of an ordered set of
   Service Functions (SF) that are to be applied to packets and/or
   frames selected as a result of classification.
   [I-D.ietf-spring-sr-service-programming] describes how a service can
   be associated with a SID and how to achieve service funtion chaining
   in SR-enabled MPLS and IPv6 networks.  In the context of Service
   Function Chaining, metadata provides contextual information about the
   data packets which traverse a Service Function Chain.

   Metadata is defined in [RFC7665]as providing "the ability to exchange
   context information between classifiers and SFs, and among SFs."

   This document discusses ways to carry metadata in SR based SFC data
   plane, including SRv6 and SR-MPLS.

2.  Metadata in SRV6 Data Plane

   [I-D.ietf-spring-sr-service-programming] defines two SRv6 TLVs,
   Opaque Metadata TLV and NSH Carrier TLV, which are used to carry
   metadata in SRH.  Another way is to carry metadata via a separate
   header.  [I-D.li-6man-enhanced-extension-header] defines a new IPv6
   extension header called metadata header, and
   [I-D.li-6man-ipv6-sfc-ifit] defines a SFC Service Metadata Option in
   metadata header.

3.  Metadata in SR-MPLS Data Plane

   Currently there is no specific solution for MPLS-SR to carry
   metadata.





Liu                     Expires September 2, 2020               [Page 2]


Internet-Draft            SR based SFC Metadata               March 2020


3.1.  Indicating Metadata in User Data Packets

   [RFC8595]chapter 12 describe how metadata is associated with user
   data packets, when using an MPLS encoding of the logical
   representation of the NSH.  A similar approach can be used in SR-
   MPLS.

   For a better understanding, the main points of the scheme will be
   described below.

                                    -------------------
                                   ~   Other Labels   ~
                                   +-------------------+
                                   |   Extension = 15  |
                                   +-------------------+
                                   |      MLI=16       |
                                   +-------------------+
                                   |  Metadata Label   |
                                   +-------------------+
                                   ~       Other       ~
                                   |      Metadata     |
                                   ~   Label Triples   ~
                                   +-------------------+
                                   |                   |
                                   ~      Payload      ~
                                   |                   |
                                    -------------------

          Figure 1: The MPLS SFC Label Stack with Metadata Label

   The Extension Label (value 15) is called special-purpose label
   [RFC7274].

   An extended special-purpose label called the Metadata Label Indicator
   (MLI) (value 16) is defined in [RFC8595]to indicate the presence of
   the Metadata Label.

   The Metadata Label (MLI) value is an index into a table of metadata
   that is programmed into the network using in-band or out-of-band
   mechanisms.Therefore, the metadata itself is not carried with the
   user data packets.

3.2.  Per Packet Metadata

   The method in section 3.1 can only be used for carrying metadata that
   is "per-SFP" or "per-flow" [RFC8393], but cannot support "per-packet"
   metadata, where the metadata must be carried on each data packet.




Liu                     Expires September 2, 2020               [Page 3]


Internet-Draft            SR based SFC Metadata               March 2020


   This document defines how "per-packet" metadata fields are carried
   with the SR-MPLS encapsulation.

   The metadata fields are defined in figure 2 and figure 3, where:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Extension Label = 15                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 MD   Indicator Label                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  MD-Type    | Length        |    RESERVED                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Fixed-Length MD Context                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 2: Type 0x1 MD Field

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Extension Label = 15                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  MD   Indicator Label                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+
      |     MD-Type    |     Length    |     Flags     | RESERVED     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //        Variable-Length  MD  Context                         //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 3: Type 0x2 MD Field

   The Extension Label (value 15) is called special-purpose label
   [RFC7274].

   MD Indicator Label (value TBA1) is used to indicate the presence of
   the metadata field in the SR-MPLS header.

   Fixed-Length MD Context: 16-bytes field to carry metadata.

   Variable-Length MD Context: a list of Service Metadata TLV [RFC8300]
   for NSH MD Type 2 [RFC8300].

   It should be noted that MD-Type cannot be 0x4 or 0x6 to prevent the
   incorrect ECMP [RFC4928].





Liu                     Expires September 2, 2020               [Page 4]


Internet-Draft            SR based SFC Metadata               March 2020


   An example of metadata carrying the in SR-MPLS header with user data
   packet is shown in Figure 4.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                     Other labels                              ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Packet as shown in Figure 2 or Figure 3        |
   +---------------------------------------------------------------+
   |                 Payload(User Data Packet)                     |
   +---------------------------------------------------------------+

              Figure 4: Metadata Field with User Data Packet

   Nodes that care about metadata need to read all the labels in the
   current label stack to find the corresponding MD Indicator Label and
   the metadata context behind it.

   The packet can also carry metadata without payload.  In this case, it
   can be used in combination with the method mentioned in section
   3.1.The MD can carry an index, which can be the same value as the
   metadata label in 3.1.In this way, the corresponding metadata table
   can be found through this index.

4.  Security Considerations

   The security considerations of SR-MPLS are discussed in [RFC8660].

5.  IANA Considerations

   TBD

6.  References

6.1.  Normative References

   [I-D.ietf-spring-sr-service-programming]
              Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca,
              d., Li, C., Decraene, B., Ma, S., Yadlapalli, C.,
              Henderickx, W., and S. Salsano, "Service Programming with
              Segment Routing", draft-ietf-spring-sr-service-
              programming-01 (work in progress), November 2019.

   [I-D.li-6man-enhanced-extension-header]
              Li, Z., Peng, S., Xie, C., and K. LEE, "Enhancement of
              IPv6 Extension Header", draft-li-6man-enhanced-extension-
              header-01 (work in progress), January 2020.



Liu                     Expires September 2, 2020               [Page 5]


Internet-Draft            SR based SFC Metadata               March 2020


   [I-D.li-6man-ipv6-sfc-ifit]
              Li, Z., Peng, S., and K. LEE, "IPv6 Encapsulation for SFC
              and IFIT", draft-li-6man-ipv6-sfc-ifit-02 (work in
              progress), September 2019.

   [RFC4928]  Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
              Cost Multipath Treatment in MPLS Networks", BCP 128,
              RFC 4928, DOI 10.17487/RFC4928, June 2007,
              <https://www.rfc-editor.org/info/rfc4928>.

   [RFC7274]  Kompella, K., Andersson, L., and A. Farrel, "Allocating
              and Retiring Special-Purpose MPLS Labels", RFC 7274,
              DOI 10.17487/RFC7274, June 2014,
              <https://www.rfc-editor.org/info/rfc7274>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <https://www.rfc-editor.org/info/rfc7665>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

   [RFC8393]  Farrel, A. and J. Drake, "Operating the Network Service
              Header (NSH) with Next Protocol "None"", RFC 8393,
              DOI 10.17487/RFC8393, May 2018,
              <https://www.rfc-editor.org/info/rfc8393>.

   [RFC8595]  Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based
              Forwarding Plane for Service Function Chaining", RFC 8595,
              DOI 10.17487/RFC8595, June 2019,
              <https://www.rfc-editor.org/info/rfc8595>.

6.2.  Informative References

   [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>.

Author's Address







Liu                     Expires September 2, 2020               [Page 6]


Internet-Draft            SR based SFC Metadata               March 2020


   Liu Yao
   ZTE Corporation
   No. 50 Software Ave, Yuhuatai Distinct
   Nanjing
   China

   Email: liu.yao71@zte.com.cn












































Liu                     Expires September 2, 2020               [Page 7]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/