BIER Z. Zhang
Internet-Draft A. Przygienda
Updates: 8401,8444 (if approved) Juniper Networks
Intended status: Standards Track A. Dolganow
Expires: April 27, 2022 Individual
H. Bidgoli
Nokia
I. Wijnands
Individual
A. Gulko
Edward Jones Wealth Management
October 24, 2021
BIER Underlay Path Calculation Algorithm and Constraints
draft-ietf-bier-bar-ipa-09
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 27, 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
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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. Compatibility . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Exceptions/Extensions to the General Rules . . . . . . . 4
3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative 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 specified.
For a particular topology X that a sub-domain is associated with, a
router MUST calculate the underlay paths according to its BCBA and
RCRA in 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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It's possible that the resulting AG is not applicable to BIER. In
that case, no BIER paths will be calculated and it is a network
design issue that an operator needs to avoid when choosing BAR/IPA.
2.1. When BAR Is Not Used
BAR value 0 is defined as "No BIER-specific algorithm is used"
[rfc8401]. This value indicates NULL BA and BC. Following the rules
defined above, the IPA value alone identifies the calculation
algorithm and constraints to be used for a particular sub-domain.
2.2. Compatibility
Currently only value 0 is used for both BAR and IPA in [RFC8401],
[RFC8444] and [I-D.ietf-bier-ospfv3-extensions], which means no
constraints, so there are no compatibility issues.
2.3. 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 a new BAR with the constraint 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., routers that do not
support BIER are not considered when applying the IGP Algorithm.
Note that if the BC and RC happen to conflict and lead to an empty
topology, then no BIER forwarding path will be found. That is a
network design issue that an operator needs to avoid when choosing
BAR/IPA.
4. IANA Considerations
No IANA Consideration is requested in this document.
5. Security Considerations
This document specifies general rules for the interaction between the
BIER Algorithm (BAR) and the IGP Algorithm (IPA) used for underlay
path calculation. It does not change the security aspects as
discussed in [RFC8279], [RFC8401], [RFC8444] and
[I-D.ietf-bier-ospfv3-extensions].
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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.
7. 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>.
[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>.
[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>.
Authors' Addresses
Zhaohui Zhang
Juniper Networks
EMail: zzhang@juniper.net
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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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