BIER Z. Zhang
Internet-Draft A. Przygienda
Updates: 8401,8444 (if approved) Juniper Networks
Intended status: Standards Track A. Dolganow
Expires: May 7, 2020 Individual
H. Bidgoli
Nokia
I. Wijnands
Cisco Systems
A. Gulko
Thomson Reuters
November 4, 2019
BIER Underlay Path Calculation Algorithm and Constraints
draft-ietf-bier-bar-ipa-06
Abstract
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",
"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."
Zhang, et al. Expires May 7, 2020 [Page 1]
Internet-Draft bier-bar-ipa November 2019
This Internet-Draft will expire on May 7, 2020.
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
(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 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 or non-default
topology [RFC5120]. The algorithm could be a generic IGP algorithm
(e.g. SPF) or could be a BIER specific one defined in the future.
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
Zhang, et al. Expires May 7, 2020 [Page 2]
Internet-Draft bier-bar-ipa November 2019
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].
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
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:
Zhang, et al. Expires May 7, 2020 [Page 3]
Internet-Draft bier-bar-ipa November 2019
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)).
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 semantics of "excluding BIER
incapable routers". That BIER specific constraint can go with any
IPA: whatever RCRA defined by the IPA are 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 secuity aspects as discussed in
[RFC8279].
6. Acknowledgements
The authors thanks Alia Atlas, Eric Rosen, Senthil Dhanaraj and many
others for their suggestions and comments. In particular, the BCBA/
Zhang, et al. Expires May 7, 2020 [Page 4]
Internet-Draft bier-bar-ipa November 2019
RCRA representation for the interaction rules is based on Alia's
write-up.
7. References
7.1. 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,
<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
Zhaohui Zhang
Juniper Networks
EMail: zzhang@juniper.net
Zhang, et al. Expires May 7, 2020 [Page 5]
Internet-Draft bier-bar-ipa November 2019
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
Cisco Systems
EMail: ice@cisco.com
Arkadiy Gulko
Thomson Reuters
EMail: arkadiy.gulko@thomsonreuters.com
Zhang, et al. Expires May 7, 2020 [Page 6]
