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 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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . [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, . 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, . [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, . 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]