BIER Z. Zhang
Internet-Draft A. Przygienda
Updates: 8401,8444 (if approved) Juniper Networks
Intended status: Standards Track A. Dolganow
Expires: August 5, 2022 Individual
H. Bidgoli
Nokia
I. Wijnands
Individual
A. Gulko
Edward Jones Wealth Management
February 1, 2022
BIER Underlay Path Calculation Algorithm and Constraints
draft-ietf-bier-bar-ipa-10
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 and RFC8444.
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
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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 August 5, 2022.
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Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Updated Definition for BAR and IPA Fields . . . . . . . . . . 3
3. General Rules for the BAR and IPA Interaction . . . . . . . . 3
3.1. When BAR Is Not Used . . . . . . . . . . . . . . . . . . 4
3.2. Exceptions/Extensions to the General Rules . . . . . . . 4
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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].
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2. Updated Definition for BAR and IPA Fields
The definition for the BAR and IPA fields in [RFC8401] and [RFC8441]
are updated as following.
IPA: IGP Algorithm. Specifies a generic Routing Algorithm (RA) and
related Routing Constraints (RC) to calculate underlay paths to reach
other BFRs. Values are from the "IGP Algorithm Types" registry
[RFC8665].
BAR: BIER Algorithm. Specifies a BIER-specific Algorithm (BA) and
BIER-specific Constraints (BC) used to either modify, enhance, or
replace the calculation of underlay paths to reach other BFRs as
defined by the IPA value. Values are allocated from the "BIER
Algorithm" registry [RFC8401].
When a BAR value is defined in a RFC or used in a deployment, the
corresponding BA and BC semantics SHOULD be specified in the RFC or
for the deployment. For an IGP Algorithm to be used as a BIER IPA,
its RA and RC semantics SHOULD be specified in a RFC or for the
deployment.
If a BAR value is not specified in a RFC but only privately used for
a deployment, it MUST be within the "240-254 Experimental Use" range
of the registry.
None of the components of the BAR or IPA can be unknown. If any of
the components is not specified, it is interpreted as "NULL"
algorithm or constraint. For example, the IGP Algorithm 0 defined in
[RFC8665] is treated as having a NULL RC, i.e., no constraints.
3. General Rules for the BAR and IPA Interaction
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 for a
sub-domain, it MUST treat the advertising router as incapable of
supporting BIER for that sub-domain (one way of handling incapable
routers is documented in Section 6.9 of [RFC8279] and additional
methods may be defined in the future).
For a particular topology X that a sub-domain is associated with, a
router MUST calculate the underlay paths according to its BAR and IPA
values in the following way:
1. Apply the BIER constraints, resulting in BC(X).
2. Apply the routing constraints, resulting in RC(BC(X)).
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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)).
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.
3.1. 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.
3.2. 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.
4. Examples
As an example, one may define a new BAR with a BIER specific
constraint of "excluding BIER incapable routers". No BIER specific
algorithm is specified, and the BIER specific constraint can go with
any IPA - whatever RC 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.
If the BC and RC happen to conflict and lead to an empty topology,
then no BIER forwarding path will be found. For example, the BC
could be "exclude BIER-incapable routers" and the RC could be
"include green links only". If all the green links are associated
with BIER-incapable routers, it results in an empty topology. That
is a network design issue that an operator needs to avoid when
choosing BAR/IPA.
In another example, a BAR value can be specified to use Steiner Tree
algorithm and used together with IPA 0 (which uses SPF algorithm).
According to the general rules, the BIER specific algorithm takes
precedence so SPF is not used.
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5. IANA Considerations
No IANA Consideration is requested in this document.
6. 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].
7. Acknowledgements
The authors thank Alia Atlas, Eric Rosen, Senthil Dhanaraj and many
others for their suggestions and comments. In particular, the
BC/BA/RC/RA representation for the interaction rules is based on
Alia's write-up.
8. 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,
<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>.
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Authors' Addresses
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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