Internet DRAFT - draft-ietf-bier-bar-ipa
draft-ietf-bier-bar-ipa
BIER Z. Zhang
Internet-Draft A. Przygienda
Updates: 8401, 8444 (if approved) Juniper Networks
Intended status: Standards Track A. Dolganow
Expires: 13 November 2022 Individual
H. Bidgoli
Nokia
I. Wijnands
Individual
A. Gulko
Edward Jones Wealth Management
12 May 2022
BIER Underlay Path Calculation Algorithm and Constraints
draft-ietf-bier-bar-ipa-13
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. This document also updates the BIER Algorithm
registry established in RFC8401.
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."
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This Internet-Draft will expire on 13 November 2022.
Copyright Notice
Copyright (c) 2022 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 Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
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 Bit-Forwarding Egress Routers
(BFERs) that are represented by bits set in the BIER header's
BitString. 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 or may not be congruent
with unicast. The algorithm could be a BIER specific algorithm or
could be a generic IGP one, e.g., Shortest Path First (SPF).
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.
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This document specifies general rules for the interaction between the
BIER Algorithm (BAR) and the IGP Algorithm (IPA) used for underlay
path calculation when other BAR and/or IPA values are used. The
semantics defined in this document update [RFC8401], [RFC8444]. This
document also updates the BIER Algorithm registry defined in
[RFC8401] by renaming the "Experimental Use" range to "Private or
Experimental Use".
2. Updated Definition for BAR and IPA Fields
The definition for the BAR and IPA fields in Section 6.1 of [RFC8401]
and Section 2.1 of [RFC8444] are updated as follows.
IPA: IGP Algorithm. Specifies a generic Routing Algorithm (RA) and
related Routing Constraints (RC) to calculate underlay paths to reach
other Bit-Forwarding Routers (BFRs). Values are from the "IGP
Algorithm Types" registry. One Octet.
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. One Octet.
When a BAR value is defined, the corresponding BA and BC semantics
SHOULD be specified. For an IGP Algorithm to be used as a BIER IPA,
its RA and RC semantics SHOULD be specified. If any of these
semantics is not specified, it MUST be 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 (see
Section 3).
If a specification is not available for a specific BAR value, its
value MUST be from the Private or Experimental Use range of the
registry.
3. General Rules for the BAR and IPA Interaction
For a particular sub-domain, all 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).
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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). If BC is NULL,
then BC(X) is X itself.
2. Apply the routing constraints, resulting in RC(BC(X)). If RC is
NULL, then RC(BC(X)) is 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)).
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
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"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.
5. IANA Considerations
This document requests the following changes to the "BIER Algorithm"
registry:
1. Rename the "Experimental Use" range to "Private or Experimental
Use"
2. Add this document as a reference
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>.
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[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>.
[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
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
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Arkadiy Gulko
Edward Jones Wealth Management
Email: arkadiy.gulko@edwardjones.com
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