BGP Extensions for BIER
draft-ietf-bier-idr-extensions-04

"leaking out" of a BIER domain.

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   These extensions are applicable in those multi-tenant data centers
   where BGP instead of IGP is used as an underlay [RFC7938].  These
   extensions may also be applicable to other BGP based network
   scenarios.

1.1.  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 RFC 2119 [RFC2119].

2.  Terminology

   This memo makes use of the terms defined in [RFC4271] and
   [I-D.ietf-bier-architecture].

3.  BIER Path Attribute

   This draft defines a new optional, transitive BGP path attribute,
   referred to as the BIER attribute.  This attribute can be attached to
   a BGP UPDATE message by the originator so as to indicate the BIER-
   specific information of a particular BFR which is identified by the
   /32 or /128 address prefix contained in the NLRI.  In other words, if
   the BIER path attribute is present, the NLRI is treated by BIER as a
   "BFR-prefix".  When creating a BIER attribute, a BFR needs to include
   one BIER TLV for every <Sub-domain, BFR-ID> pair that it supports.
   The attribute type code for the BIER Attribute is TBD.  The value
   field of the BIER Attribute contains one or more BIER TLV as shown 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Type=TBD            |            Length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Sub-domain   |            BFR-ID             |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                                                               ~
       |                           Sub-TLVs                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+..........................
                             Figure 1:BIER TLV

      Type: Two octets encoding the BIER TLV Type: TBD.

      Length: Two octets encoding the length in octets of the TLV,
      including the type and length fields.  The length is encoded as an
      unsigned binary integer.  (Note that the minimum length is 8,
      indicating that no sub-TLV is present.)

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      Sub-domain: a one-octet field encoding the sub-domain ID
      corresponding to the BFR-ID.

      BFR-ID: a two-octet field encoding the BFR-ID.

      Sub-TLVs: contains one or more sub-TLV.  The BIER MPLS
      Encapsulation sub-TLV is one of such sub-TLVs.

   The BIER MPLS Encapsulation sub-TLV is encoded 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Type=TBD            |         Length=12             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                Label Range Base               |Lbl Range Size |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      BSL      |                    Reserved                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 2:BIER MPLS Encapsulation sub-TLV

      Type:TBD

      Length:12

      Label Range Size: a one-octet field indicating the size of the
      label range.

      Label Range Base: a 3-octet field where the 20 rightmost bits
      represent the first label in the label range while the other bits
      MUST be set to 0 when transmitting, and MUST be ignored upon
      receipt.

      BSL: a one-octet field indicating the length of the Bitstring in
      4-octets.  The field MUST be filled with one of the valid BSL
      values as specified in [I-D.ietf-bier-architecture].  Upon
      receiving a BSL-TLV containing an invalid BSL value, it MUST be
      ignored.

4.  Originating BIER Attribute

   An implementation that supports the BIER attribute MUST support a
   policy to enable or disable the creation of the BIER attribute and
   its attachment to specific BGP routes.  An implementation MAY disable
   the creation of the BIER attribute unless explicitly configured to do
   so otherwise.  A BGP speaker MUST only attach the locally created
   BIER attribute to a BGP UPDATE message in which at least one of its
   BFR-prefixes is contained in the NLRI

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5.  Restrictions on Sending/Receiving

   An implementation that supports the BIER attribute MUST support a
   per-EBGP-session policy, that indicates whether the attribute is
   enabled or disabled for use on that session.  The BIER attribute MUST
   NOT be sent on any EBGP peers for which the session policy is not
   configured.  If an BIER attribute is received on a BGP session for
   which session policy is not configured, then the received attribute
   MUST be treated exactly as if it were an unrecognised non-transitive
   attribute.  That is, "it MUST be quietly ignored and not passed along
   to other BGP peers".

   To prevent the BIER attribute from "leaking out" of an BIER domain,
   each BGP router on the BIER domain MUST support an outbound route
   announcement policy.  Such a policy MUST be disabled on each EBGP
   session by default unless explicitly configured.

6.  Deployment Considerations

   It's assumed by this document that the BIER domain is aligned with
   the Administrative Domain (AD) which are composed of multiple ASes
   (either private or public ASes).  Use of the BIER attribute in other
   scenarios is outside the scope of this document.

   Since the BIER attribute is an optional, transitive BGP path
   attribute, a non-BFR BGP speakers could still advertise the received
   route with a BIER attribute.  This is desirable in the incremental
   deployment scenario where a BGP speaker could tunnel a BIER packet or
   the payload of a BIER packet to a BFER directly if the BGP next-hop
   of the route for that BFER is a non-BFR.  Furthermore, a BGP speaker
   is allowed to tunnel a BIER packet to the BGP next-hop if these two
   BFR-capable BGP neighbors are not directly connected (e.g., multi-hop
   EBGP).

7.  Acknowledgements

   Thanks a lot for Eric Rosen and Peter Psenak for their valuable
   comments on this document.

8.  IANA Considerations

   IANA is requested to assign a codepoint in the "BGP Path Attributes"
   registry to the BIER attribute.  IANA shall create a registry for
   "BGP BIER Attribute Types".  The type field consists of two octets,
   with possible values from 1 to 655355 (The value 0 is "reserved".)
   The allocation policy for this field is to be "First Come First
   Serve".  Type codes should be allocated for BIER TLV and BIER MPLS
   Encapsulation sub-TLV respectively.

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9.  Security Considerations

   This document introduces no new security considerations beyond those
   already specified in [RFC4271].

10.  References

10.1.  Normative References

   [I-D.ietf-bier-architecture]
              Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and
              S. Aldrin, "Multicast using Bit Index Explicit
              Replication", draft-ietf-bier-architecture-08 (work in
              progress), September 2017.

   [I-D.ietf-bier-mpls-encapsulation]
              Wijnands, I., Rosen, E., Dolganow, A., Tantsura, J.,
              Aldrin, S., and I. Meilik, "Encapsulation for Bit Index
              Explicit Replication in MPLS and non-MPLS Networks",
              draft-ietf-bier-mpls-encapsulation-12 (work in progress),
              October 2017.

   [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>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

10.2.  Informative References

   [I-D.ietf-bier-use-cases]
              Kumar, N., Asati, R., Chen, M., Xu, X., Dolganow, A.,
              Przygienda, T., arkadiy.gulko@thomsonreuters.com, a.,
              Robinson, D., Arya, V., and C. Bestler, "BIER Use Cases",
              draft-ietf-bier-use-cases-05 (work in progress), July
              2017.

   [RFC7938]  Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
              BGP for Routing in Large-Scale Data Centers", RFC 7938,
              DOI 10.17487/RFC7938, August 2016,
              <https://www.rfc-editor.org/info/rfc7938>.

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Authors' Addresses

   Xiaohu Xu (editor)
   Huawei

   Email: xuxh.mail@gmail.com

   Mach Chen
   Huawei

   Email: mach.chen@huawei.com

   Keyur Patel
   Arrcus, Inc.

   Email: keyur@arrcus.com

   IJsbrand Wijnands
   Cisco

   Email: ice@cisco.com

   Antoni Przygienda
   Juniper

   Email: prz@juniper.net

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