BIER Underlay Path Calculation Algorithm and Constraints
draft-ietf-bier-bar-ipa-08

Document Type Active Internet-Draft (bier WG)
Authors Zhaohui Zhang  , Tony Przygienda  , Andrew Dolganow  , Hooman Bidgoli  , IJsbrand Wijnands  , Arkadiy Gulko 
Last updated 2021-10-12 (latest revision 2021-09-29)
Replaces draft-zzhang-bier-bar-ipa
Stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Formats pdf htmlized bibtex
Stream WG state Submitted to IESG for Publication
Document shepherd Greg Mirsky
Shepherd write-up Show (last changed 2020-09-24)
IESG IESG state AD Evaluation::Revised I-D Needed
Action Holders
Consensus Boilerplate Yes
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Responsible AD Alvaro Retana
Send notices to Greg Mirsky <gregimirsky@gmail.com>, aretana.ietf@gmail.com
BIER                                                            Z. Zhang
Internet-Draft                                             A. Przygienda
Updates: 8401,8444 (if approved)                        Juniper Networks
Intended status: Standards Track                             A. Dolganow
Expires: April 2, 2022                                        Individual
                                                              H. Bidgoli
                                                                   Nokia
                                                             I. Wijnands
                                                              Individual
                                                                A. Gulko
                                          Edward Jones Wealth Management
                                                      September 29, 2021

        BIER Underlay Path Calculation Algorithm and Constraints
                       draft-ietf-bier-bar-ipa-08

Abstract

   This document specifies general rules for the interaction between the
   BIER Algorithm (BAR) and the IGP Algorithm (IPA) used for underlay
   path calculation.  The semantics defined in this document update
   RFC8401, RFC8444, and draft-ietf-bier-ospfv3-extensions.

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.

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 April 2, 2022.

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Copyright Notice

   Copyright (c) 2021 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.

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.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   In the 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.  The paths are
   calculated in the underlay topology for each sub-domain following a
   calculation algorithm specific to the sub-domain.  The topology or
   algorithm may be congruent with unicast.  The algorithm could be a
   generic IGP algorithm (e.g.  SPF) or could be a BIER specific one
   defined in the future.

   This document specifies general rules for the interaction between the
   BIER Algorithm (BAR) and the IGP Algorithm (IPA) used for underlay
   path calculation.  The semantics defined in this document update
   [RFC8401], [RFC8444], and [I-D.ietf-bier-ospfv3-extensions].

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2.  General Rules for the BAR and IPA fields

   For a particular sub-domain, all BIER Forwarding Routers (BFRs) MUST
   be provisioned with and signal the same BAR and IPA values.  If a BFR
   discovers another BFR advertising different BAR or IPA value, it MUST
   treat the advertising router as incapable of supporting BIER (one way
   of handling incapable routers is documented in Section 6.9 of
   [RFC8279] and additional methods may be defined in the future).

   Both BAR and IPA 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 an IPA value corresponds to an
   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 clearly specified.

   For a particular topology X (which could be a default topology or
   non-default 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.

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

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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.  Examples

   As an example, one may define BAR=x with the semantics of "excluding
   BIER incapable routers".  That BIER specific constraint can go with
   any IPA: whatever RCRA defined by the IPA is augmented with
   "excluding BIER incapable routers", i.e., BIER incapable routers are
   not put onto the candidate list during SPF calculation.

   Note that if the BC and RC happen to conflict and lead to an empty
   topology, then no native BIER forwarding path will be found.  That is
   a network design issue that an operator need to avoid when choosing
   BAR/IPA.

4.  IANA Considerations

   No IANA Consideration is requested in this document.

5.  Security Considerations

   This document does not change the security aspects as discussed in
   [RFC8279].

6.  Acknowledgements

   The authors thank 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
   write-up.

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7.  References

7.1.  Normative References

   [I-D.ietf-bier-ospfv3-extensions]
              Psenak, P., Nainar, N. K., and I. Wijnands, "OSPFv3
              Extensions for BIER", draft-ietf-bier-ospfv3-extensions-04
              (work in progress), May 2021.

   [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>.

   [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,
              <https://www.rfc-editor.org/info/rfc8401>.

   [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,
              <https://www.rfc-editor.org/info/rfc8444>.

7.2.  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,
              <https://www.rfc-editor.org/info/rfc5120>.

   [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>.

Authors' Addresses

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   Zhaohui Zhang
   Juniper Networks

   EMail: zzhang@juniper.net

   Antoni Przygienda
   Juniper Networks

   EMail: prz@juniper.net

   Andrew Dolganow
   Individual

   EMail: adolgano@gmail.com

   Hooman Bidgoli
   Nokia

   EMail: hooman.bidgoli@nokia.com

   IJsbrand Wijnands
   Individual

   EMail: ice@braindump.be

   Arkadiy Gulko
   Edward Jones Wealth Management

   EMail: arkadiy.gulko@edwardjones.com

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