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Versions: 00 01 02 draft-xie-bier-ipv6-encapsulation

Network Working Group                                             J. Xie
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                                 L. Geng
Expires: March 5, 2019                                           L. Wang
                                                            China Mobile
                                                                  G. Yan
                                                              M. McBride
                                                                  Y. Xia
                                                                  Huawei
                                                       September 1, 2018


            Encapsulation for BIER in Non-MPLS IPv6 Networks
                  draft-xie-bier-6man-encapsulation-02

Abstract

   Bit Index Explicit Replication (BIER) introduces a new multicast-
   specific BIER Header.  Currently BIER has two types of encapsulation
   formats: one is MPLS encapsulation, the other is Ethernet
   encapsulation.  This document proposes a BIER IPv6 encapsulation for
   Non-MPLS IPv6 Networks using an IPv6 Destination Option extension
   header.

Requirements Language

   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].

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 March 5, 2019.





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Copyright Notice

   Copyright (c) 2018 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
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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
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Statement and Requirements  . . . . . . . . . . . . .   3
     3.1.  Problem Statement . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   3
   4.  IPv6 BIER Encapsulation . . . . . . . . . . . . . . . . . . .   4
     4.1.  Considerations  . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  IPv6 BIER Destination Option  . . . . . . . . . . . . . .   4
     4.3.  The whole IPv6 header for BIER packets  . . . . . . . . .   5
   5.  IPv6 BIER Forwarding  . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  Appendix A - BIER over IPv6 SRH Tunnel  . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Bit Index Explicit Replication (BIER) [RFC8279] is an architecture
   that provides optimal multicast forwarding without requiring
   intermediate routers to maintain any per-flow state by using a
   multicast-specific BIER header.  [RFC8296] defines two types of BIER
   encapsulation to run on physical links: one is BIER MPLS
   encapsulation to run on various physical links that support MPLS, the
   other is BIER Ethernet encapsulation to run on ethernet links, with
   an ethertype 0xAB37.  This document proposes a BIER IPv6
   encapsulation for Non-MPLS IPv6 Networks using an IPv6 Destination
   Option extension header.



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2.  Terminology

   Readers of this document are assumed to be familiar with the
   terminology and concepts of the documents listed as Normative
   References.

3.  Problem Statement and Requirements

3.1.  Problem Statement

   MPLS is a very popular and successful encapsulation.  With MPLS
   encapsulation, packets forwarding can not only run on various
   physical links hop-by-hop, but also leverage the MPLS bypass tunnel
   to gain the "fast reroute" capability.

   This same label benefit is also available for BIER by using an MPLS
   encapsulation.  For example, an MPLS-encapsulated BIER packet can be
   forwarding on various physical links hop-by-hop, as well as on any
   MPLS bypass tunnels to support "fast reroute".

   With a BIER Ethernet encapsulation, however, a packet can not be
   forwarded on any other type of links except for ethernet links in
   hop-by-hop case.  It can not run on an MPLS bypass tunnel to support
   "fast reroute" either.

   In an IPv6 network, there are considerations of using a non-MPLS
   encapsulation for unicast as the data-plane, such as SRH defined in
   [I-D.ietf-6man-segment-routing-header], where the function of a
   bypass tunnel uses an SRH header, with one or many Segments (or
   SIDs), instead of MPLS Labels.  In such case, it is expected to have
   a BIER IPv6 encapsulation, which can run on IPv6 to be compliant with
   various kind of physical link in hop-by-hop case, as well as on SRH
   tunnel to have the significant benefit of "fast reroute" and so on.

3.2.  Requirements

   This chapter lists the BIER IPv6 encapsulation requirements needed to
   make the deployment of BIER on IPv6 network with SRH data-plane the
   same as on IPv4/IPv6 network with MPLS data-plane.  These BIER IPv6
   encapsulation requirements should provide similar benefits to MPLS
   encapsulation such as "fast reroute" or "run on any link or
   interface".

   1.  The listed requirements MUST be supported with any L1/L2 over
       which BIER layer can be realized.

   2.  It SHOULD support a hop-by-hop replication to multiple
       destinations in a BIER Domain.



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   3.  It SHOULD support BIER on an "SRH tunnel".

   4.  It SHOULD align with the recommendations of the 6MAN working
       group.

4.  IPv6 BIER Encapsulation

4.1.  Considerations

   BIER is generally a hop-by-hop and one-to-many architecture, and thus
   the IPv6 Destination Address (DA) being a Multicast Address is a
   proper approach for both the two diagrams in BIER IPv6 encapsulation.
   It is also required for a BIER IPv6 encapsulation to include the BIER
   Header ([RFC8296]) as an IPv6 Extension Header, to pilot the hop-by-
   hop BIER replication.

   According to [RFC8200], [RFC6564], and [RFC7045], a new defined IPv6
   extention header is not recommended, and an IPv6 Destination Option
   extension header is suitable and recommended for such a well-known
   BIER header as its Option.

4.2.  IPv6 BIER Destination Option

   The IPv6 BIER Destination Option is carried by the IPv6 Destination
   Option Header (indicated by a Next Header value 60).  It is
   initialized in a packet sent by an IPv6 BFIR router to inform the
   following BFR routers in an IPv6 BIER domain to replicate to
   destination BFER routers hop-by-hop.

   The IPv6 BIER Destination Option is encoded in type-length-value
   (TLV) format as follows:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Next Header  |  Hdr Ext Len  |  Option Type  | Option Length |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~          Non-MPLS BIER Header (defined in RFC8296)            ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 1: IPv6 BIER Destination Option

   Next Header  8-bit selector.  Identifies the type of header
      immediately following the Destination Options header.





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   Hdr Ext Len  8-bit unsigned integer.  Length of the Destination
      Options header in 8-octet units, not including the first 8 octets.

   Option Type  TBD.  Need to be allocated by IANA.

   Option Length  8-bit unsigned integer.  Length of the option, in
      octets, excluding the Option Type and Option Length fields.

   Non-MPLS BIER Header  The Non-MPLS BIER Header defined in RFC8296,
      including the BIFT-id.  The function of TTL field is replaced by
      the Hop Limit field in IPv6 header and MUST be set to a non-zero
      value.  The function of Entropy field is replaced by the Flow
      Label field in IPv6 header and MUST be set to zero value.

4.3.  The whole IPv6 header for BIER packets

   [RFC8200] specifies that the Destination Option Header can be located
   either before the Routing Header or after the Routing Header.
   However, this document requires that the Destination Option Header
   with a BIER Destination Option TLV is always located after the
   Routing Header if the Routing Header is present.

   This is because the BIER header is always handled after the tunnels
   (or bypass tunnels) have been handled.  BIER MPLS encapsulation has
   the same behavior.  To quote [RFC8296]:

   o  It is crucial to understand that in an MPLS network the first four
      octets of the BIER encapsulation header are also the last four
      octets of the MPLS header.  Therefore, any prior MPLS label stack
      entries MUST have the S bit (see [RFC3032]) clear (i.e., the S bit
      must be 0).

   Other IPv6 extension headers are not commonly used in the current
   Internet.  For Example, [RFC6744] says that "IPv6 Destination Options
   headers, and the options carried by such headers, are extremely
   uncommon in the deployed Internet".  [RFC6564] says that "Extension
   headers, with the exception of the Hop-by-Hop Options header, are not
   usually processed on intermediate nodes", and that "Reports from the
   field indicate that some IP routers deployed within the global
   Internet are configured either to ignore the presence of headers with
   hop-by-hop behavior or to drop packets containing headers with hop-
   by-hop behavior."

   Such IPv6 extension headers will even be more uncommon when a BIER
   encapsulation is used in data-plane forwarding.  The entire IPv6
   header, with BIER encapsulation and Routing Header, is expected to
   look like this:




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      IPv6 header [Multicast Address in DA]

      Hop-by-Hop Options header [No use]

      Destination Options header [No use]

      Routing header [SRH Header may be used, Appendix A]

      Fragment header [No use ]

      Authentication header [No use]

      Encapsulating Security Payload header [No use]

      Destination Options header [BIER header in BIER Option TLV]

      Upper-layer header [BIER payload]

   In a hop-by-hop BIER IPv6 replication scenario, there is only an IPv6
   header with DA being a "BIER specific" Multicast address, and an IPv6
   Destination Option header with a BIER destination option TLV.

   BIER header has a 'proto' field to identify the type of BIER packet
   payload, and the IANA has created a registry called "BIER Next
   Protocol Identifiers" to assign the value.  That means the 'Upper-
   layer header' of a BIER packet have already been identified by the
   'proto' field of the BIER header in the Destination Option Header.
   Thus the 'Next Header' in the Destination Option Header is not need
   to identify the 'Upper-layer header' any more, and is recommended to
   be set to 'No Next Header (value 59)'.

   Procedures for encapsulating a BIER IPv6 packet in SRH tunnel are
   outside the scope of this document.

   Procedures for encapsulating a BIER IPv6 packet in other types of
   tunnels are outside the scope of this document.

5.  IPv6 BIER Forwarding

   In an IPv6 BIER domain, the Multicast Address of the IPv6 DA in an
   incoming BIER IPv6 packet indicates the BIER information of this
   'host', and the packet will be forwarded according to the BIER Header
   in the BIER Destination Option TLV in the IPv6 Destination Option
   extension header.  A router is required to ignore the IPv6 BIER
   Destination Option if the IPv6 Destination Address of a packet is not
   a multicast address, or is a multicast adddress without indicating
   the BIER information of this 'host'.




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   Below is the procedure that a BFR uses for forwarding a BIER IPv6
   encapsulated packet.

   1.  Read the IPv6 header, get the the IPv6 DA, and get the indication
       of the multicast address if the IPv6 DA is a multicast address.
       The case when IPv6 DA not being a multicast address is outside
       the scope of this document.

   2.  If the multicast address is interested by this router, and the
       'Next Header' of the IPv6 header indicates a IPv6 Destination
       Option Header, then read the IPv6 Destination Option Header, and
       get the BIER Option (BIER Header).  The case when the multicast
       address not being interested by this router is outside the scope
       of this document.

   3.  The following steps are the same as step 1 to 9 described in
       chapter 6.5 in [RFC8279].  One difference need to point out is
       that, the copied packet includes a IPv6 header, a IPv6
       Destination Header and its BIER Destination Option Type and
       Option Length before the BIER Header.  If the copied packet is
       forwarded to a BFR-NBR, the 'Hop Limit' field of the IPv6 header
       MUST be decremented, whereas the TTL in the BIER header MUST be
       unchanged.

   Procedures for forwarding a BIER IPv6 packet in SRH tunnel, and hand-
   off to a hop-by-hop replication, can refer to Appendix A.

   Procedures for forwarding a BIER IPv6 packet in other types of
   tunnels, and hand-off to a hop-by-hop replication, are outside the
   scope of this document.

6.  Security Considerations

   An IPv6 BIER Destination Option with Multicast Address Destination
   would be used only when an IPv6 BIER state with the specific
   Multicast Address Destination has been built by the control-plane.
   Otherwise the packet with an IPv6 BIER Destination Option will be
   discarded.

7.  IANA Considerations

   Allocation is expected from IANA for a BIER Destination Option Type
   codepoint from the "Destination Options and Hop-by-Hop Options" sub-
   registry of the "Internet Protocol Version 6 (IPv6) Parameters"
   registry [RFC2780] at <https://www.iana.org/assignments/
   ipv6-parameters/>.





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   Allocation is expected from IANA for a BIER Multicast Address from
   the "Variable Scope Multicast Addresses" sub-registry of the "IPv6
   Multicast Address Space Registry" registry at
   <https://www.iana.org/assignments/ipv6-multicast-addresses/>.

8.  Acknowledgements

   TBD.

9.  Appendix A - BIER over IPv6 SRH Tunnel

   In a Non-MPLS IPv6 Network, BIER may be deployed in a hop-by-hop
   manner, or possibly be deployed through an SRH tunnel either for
   "bypassing Non-capable BIER routers" or "fast rerouting".  Here is an
   example where a packet is firstly forwarded through an SRH tunnel and
   then through a hop-by-hop BIER domain.

   When a router along the Segment Routing path receives an IPv6 BIER
   packet with an SRH header, and if the IPv6 destination address is not
   one of the router's address, then the packet is forwarded by an IPv6
   FIB lookup of the destination address and none of the IPv6 extension
   headers will be checked.  If the IPv6 Destination Address is one of
   the router's address, and also one of the router's Segment (or SID)
   of some type, then the router will do a specific function indicated
   by the Segment, as defined in
   [I-D.filsfils-spring-srv6-network-programming].  If the IPv6
   Destination Address is a specific type of Segment, called BIER
   Segment or BIER SID, then the according function is called Endpoint
   BIER function or 'End.BF' function for short.

   When router receives a packet destined to X and X is a local End.BF
   SID, the router does:

   1.    IF SL > 0
   2.      decrement SL
   3.      update IPv6 DA with SRH[SL]
   4.      IF SL = 0 & STATE(SRH[0]) = BIER
   5.        update IPv6 header NH with SRH NH
   6.        pop the SRH
   7.        forward the updated packet
   8.      ELSE
   9.        drop the packet
   10.   ELSE
   11.     drop the packet

                         Figure 2: End.BF Function





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   The End.BF function is used for the SRH tunnel destination router to
   terminate the source-routing SRH forwarding and begin the hop-by-hop
   BIER IPv6 forwarding.  After the SRH header is popped, the multicast
   address in the updated IPv6 Destination Address indicates the BIER
   information of this 'host', and the packet will be forwarded
   according to the BIER Header in the BIER Destination Option TLV in
   the IPv6 Destination Option extension header of this 'host'.

   In the following hop-by-hop forwarding procedure, the IPv6
   Destination Address in an incoming packet indicates the BIER
   information of this 'host', and the packet will be forwarded
   according to the BIER Header in the BIER Destination Option TLV in
   the IPv6 Destination Option extension header.  A router is required
   to ignore the IPv6 BIER Destination Option if the IPv6 Destination
   Address of a packet is not a multicast address, or is a multicast
   adddress without indicating the BIER information of this 'host'.

10.  References

10.1.  Normative References

   [I-D.filsfils-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J.,
              daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
              Network Programming", draft-filsfils-spring-srv6-network-
              programming-05 (work in progress), July 2018.

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and
              d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-14 (work in
              progress), June 2018.

   [RFC6564]  Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and
              M. Bhatia, "A Uniform Format for IPv6 Extension Headers",
              RFC 6564, DOI 10.17487/RFC6564, April 2012,
              <https://www.rfc-editor.org/info/rfc6564>.

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045,
              DOI 10.17487/RFC7045, December 2013,
              <https://www.rfc-editor.org/info/rfc7045>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.




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   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

   [RFC8296]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
              for Bit Index Explicit Replication (BIER) in MPLS and Non-
              MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
              2018, <https://www.rfc-editor.org/info/rfc8296>.

10.2.  Informative References

   [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>.

Authors' Addresses

   Jingrong Xie
   Huawei Technologies

   Email: xiejingrong@huawei.com


   Liang Geng
   China Mobile
   Beijing 10053

   Email: gengliang@chinamobile.com


   Lei Wang
   China Mobile
   Beijing 10053

   Email: wangleiyjy@chinamobile.com


   Gang Yan
   Huawei

   Email: yangang@huawei.com






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   Mike McBride
   Huawei

   Email: mmcbride7@gmail.com


   Yang Xia
   Huawei

   Email: yolanda.xia@huawei.com









































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