BIER                                                            Z. Zhang
Internet-Draft                                             A. Przygienda
Updates: 8401,8444 (if approved)                        Juniper Networks
Intended status: Standards Track                             A. Dolganow
Expires: November 30, 2019                                    H. Bidgoli
                                                             I. Wijnands
                                                           Cisco Systems
                                                                A. Gulko
                                                         Thomson Reuters
                                                            May 29, 2019

        BIER Underlay Path Calculation Algorithm and Constraints


   This document specifies general rules for interaction between the BAR
   (BIER Algorithm) and IPA (IGP Algorithm) fields defined in ISIS/
   OSPFv2 Extensions for BIER.  The semantics for the BAR and IPA fields
   (when both or any of them is non-zero) defined in this document
   updates the semantics defined in RFC8444/RFC8401.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 30, 2019.

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Copyright Notice

   Copyright (c) 2019 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
   ( 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  General Rules for the BAR and IPA fields  . . . . . . . . . .   3
     2.1.  When BAR Is Not Used  . . . . . . . . . . . . . . . . . .   4
     2.2.  Exceptions/Extensions to the General Rules  . . . . . . .   4
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   In Bit Index Explicit Replication (BIER) architecture [RFC8279],
   packets with a BIER encapsulation header are forwarded to the
   neighbors on the underlay paths towards the BFERs.  For each sub-
   domain, the paths are calculated in the underlay topology for the
   sub-domain, following a calculation algorithm specific to the sub-
   domain.  The <topology, algorithm> could be congruent or incongruent
   with unicast.  The topology could be a default topology, a multi-
   topology [RFC5120] topology.  The algorithm could be a generic IGP
   algorithm (e.g.  SPF) or could be a BIER specific one defined in the

   In [RFC8401] and [RFC8444], an 8-bit BAR (BIER Algorithm) field and
   8-bit IPA (IGP Algorithm) field are defined to signal the BIER
   specific algorithm and generic IGP Algorithm respectively and only
   value 0 is allowed for both fields in those two documents.  This
   document specifies the general rules for the two fields and their
   interaction when either or both fields are not 0, and updates their
   semantics defined in [RFC8444] and [RFC8401].

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2.  General Rules for the BAR and IPA fields

   For a particular sub-domain, all routers SHOULD be provisioned with
   and signal the same BAR and IPA values.  When a BFR discovers another
   BFR advertising different BAR or IPA value from its own provisioned,
   it MUST treat the advertising BFR as incapable of supporting BIER for
   the sub-domain.  How incapable routers are handled is outside the
   scope of this document.

   It is expected that both the BAR and IPA values could have both
   algorithm and constraints semantics.  To generalize, we introduce the
   following terms:

   o  BC: BIER-specific Constraints

   o  BA: BIER-specific Algorithm

   o  RC: Generic Routing Constraints

   o  RA: Generic Routing Algorithm

   o  BCBA: BC + BA

   o  RCRA: RC + RA

   A BAR value corresponds to a BCBA, and a IPA value corresponds to a
   RCRA.  Any of the RC/BC/BA could be "NULL", which means there are no
   corresponding constraints or algorithm.

   When a new BAR value is defined, its corresponding BC/BA semantics
   MUST be specified.  For a new IGP Algorithm to be used as a BIER IPA,
   its RC/RA semantics MUST also be clear.

   For a particular topology X (which could be a default topology or
   multi-topolgy topology) that a sub-domain is associated with, a
   router calculates the underlay paths according to its provisioned
   BCBA and RCRA the following way:

   1.  Apply the BIER constraints, resulting in BC(X).

   2.  Apply the routing constraints, resulting in RC(BC(X)).

   3.  Select the algorithm AG as following:

       A.  If BA is NULL, AG is set to RA.

       B.  If BA is not NULL, AG is set to BA.

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   4.  Run AG on RC(BC(X)).

2.1.  When BAR Is Not Used

   The BIER Algorithm registry established by [RFC8401] and also used in
   [RFC8444] has value 0 for "No BIER specific algorithm is used".  That
   translates to NULL BA and NULL BC.  Following the rules defined
   above, the IPA value alone identifies the calculation algorithm and
   constraints to be used for a particular sub-domain when BAR is 0.

2.2.  Exceptions/Extensions to the General Rules

   Exceptions or extensions to the above general rules may be specified
   in the future for specific BAR and/or IPA values.  When that happens,
   compatibility with defined BAR and/or IPA values and semantics need
   to be specified.

3.  IANA Considerations

   No IANA Consideration is requested in this document.

4.  Acknowledgements

   The authors thanks Alia Atlas, Eric Rosen, Senthil Dhanaraj and many
   others for their suggestions and comments.  In particular, the BCBA/
   RCRA representation for the interaction rules is based on Alia's

5.  References

5.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC8401]  Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z.
              Zhang, "Bit Index Explicit Replication (BIER) Support via
              IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018,

   [RFC8444]  Psenak, P., Ed., Kumar, N., Wijnands, IJ., Dolganow, A.,
              Przygienda, T., Zhang, J., and S. Aldrin, "OSPFv2
              Extensions for Bit Index Explicit Replication (BIER)",
              RFC 8444, DOI 10.17487/RFC8444, November 2018,

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5.2.  Informative References

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,

   [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,

Authors' Addresses

   Zhaohui Zhang
   Juniper Networks


   Antoni Przygienda
   Juniper Networks


   Andrew Dolganow


   Hooman Bidgoli


   IJsbrand Wijnands
   Cisco Systems


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   Arkadiy Gulko
   Thomson Reuters


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