BIER                                                            Z. ZhangInternet-Draft                                          Juniper NetworksIntended status: Standards Track                         4 December 2024Expires: 7 June 2025                      BIER Penultimate Hop Popping                         draft-ietf-bier-php-16Abstract   This document specifies a mechanism for Penultimate Hop Popping (PHP)   in the Bit Index Explicit Replication (BIER) architecture.  PHP   enables the removal of the BIER header by the penultimate router,   thereby reducing the processing burden on the final router in the   delivery path.  This extension to BIER enhances operational   efficiency by optimizing packet forwarding in scenarios where the   final hop's capabilities or requirements necessitate such handling.   The document details the necessary extensions to the BIER   encapsulation and forwarding processes to support PHP, providing   guidance for implementation and deployment within BIER-enabled   networks.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 7 June 2025.Zhang                      Expires 7 June 2025                  [Page 1]Internet-Draft                  bier-php                   December 2024Copyright Notice   Copyright (c) 2024 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   described in Section 4.e of the Trust Legal Provisions and are   provided without warranty as described in the Revised BSD License.Table of Contents   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2   2.  Specifications  . . . . . . . . . . . . . . . . . . . . . . .   3     2.1.  Signaling . . . . . . . . . . . . . . . . . . . . . . . .   4     2.2.  BIRT/BIFT Calculation . . . . . . . . . . . . . . . . . .   5   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   5   4.  Operational Considerations  . . . . . . . . . . . . . . . . .   5   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   91.  Introduction   The Bit Index Explicit Replication (BIER) architecture [RFC8279]   consists of three layers: the "routing underlay", the "BIER layer",   and the "multicast flow overlay".  The multicast flow overlay is   responsible for allowing BIER Forwarding Egress Routers (BFERs) to   signal to BIER Forwarding Ingress Routers (BFIRs) their interest in   receiving specific multicast flows, enabling BFIRs to encode the   appropriate bitstring for forwarding by the BIER layer.   Multicast Virtual Private Network (MVPN) [RFC6513] [RFC6514] and   Ethernet VPN (EVPN) [RFC7432] are two analogous overlays in which BGP   Auto-Discovery routes for MVPN/EVPN are exchanged among all Provider   Edge (PE) routers to signal which PEs should receive multicast   traffic for all or certain flows.  Typically, a consistent provider   tunnel type is used for traffic delivery to all receiving PEs.Zhang                      Expires 7 June 2025                  [Page 2]Internet-Draft                  bier-php                   December 2024   In a deployment scenario where MVPN/EVPN is in use and a sufficient   number of provider routers support BIER, BIER can become the   preferred provider tunnel type [RFC8556] [RFC9624] . However, some   PEs may lack the capability to support BIER forwarding (they are   referred to as BIER-incapable in this document).  While it is   possible for an ingress PE to send traffic to some PEs using one type   of tunnel and to others using a different type, such a procedure can   be complex and may result in suboptimal forwarding.   A potential solution to this issue is the use of Penultimate Hop   Popping (PHP), whereby the upstream BIER Forwarding Router (BFR) pops   the BIER header [RFC8296] and transmits the payload without BIER   encapsulation.  This transmission can occur either directly or   indirectly through any type of tunnel to the PE.  This mechanism is   analogous to Multi-Protocol Label Switching (MPLS) PHP, except that   the BIER header is removed.   The transition from an existing MVPN/EVPN deployment with   conventional provider tunnels to a BIER-based solution, where some   PEs are not BIER-capable, can be incremental.  Initially, all PEs are   upgraded to support BIER in the control plane, with those unable to   perform BIER forwarding requesting PHP.  Subsequently, BIER-capable   ingress PEs can independently and incrementally switch to BIER   transport.   While MVPN/EVPN is used as an example in the above discussion, BIER   PHP is applicable to any scenario where the multicast flow overlay   edge router does not support BIER, provided that the edge router does   not need to identify the transmitting BFIR or participate in BIER   Operations, Administration, and Maintenance (OAM) procedures.   This approach is effective when a BIER-incapable PE only needs to   receive multicast traffic.  However, if the PE also needs to send   multicast traffic, it must perform Ingress Replication to a BIER-   capable helper PE, which will then relay the packet to other PEs.   The helper PE may be a Virtual Hub as defined in [RFC7024] for MVPN   and [I-D.ietf-bess-evpn-virtual-hub] for EVPN, or an AR-Replicator as   defined in [RFC9574] for EVPN.2.  Specifications   The BIER Penultimate Hop Popping (PHP) mechanism is designed   specifically for scenarios where a multicast flow overlay router   within a BIER domain does not support BIER forwarding, either   completely or for specific BitStringLengths (BSL).  In the latter   case, PHP applies only to BIER packets with those particular BSLs.   If the flow overlay router were capable of BIER forwarding, it would   function as a BFER, and PHP would not be performed by the penultimateZhang                      Expires 7 June 2025                  [Page 3]Internet-Draft                  bier-php                   December 2024   hop.   The procedures outlined in this section are applicable only if,   through means outside the scope of this document, it is established   that all potential penultimate hop BFRs are capable of supporting PHP   (i.e., able to remove the BIER header when forwarding to a requesting   flow overlay router) and that the payload following the BIER header   is one of the following:   *  MPLS packets with a downstream-assigned label at the top of the      stack (i.e., the Proto field in the BIER header is set to 1).  For      instance, a label from a Domain-wide Common Block (DCB) as      specified in [RFC9573].   *  IPv4/IPv6 multicast packets for which the Reverse Path Forwarding      (RPF) check is disabled.2.1.  Signaling   In IS-IS signaling, a sub-TLV nested within another sub-TLV is   referred to as a sub-sub-TLV (and further levels are possible, such   as sub-sub-sub-TLV).  In other signaling protocols, a sub-TLV nested   within another sub-TLV is still referred to as a sub-TLV.  For   convenience, this document uses the term "sub-TLV" even when   referring to a sub-sub-TLV in IS-IS, as there is no ambiguity in the   terminology (e.g., MPLS Encapsulation).   A BIER-incapable router, when functioning as a multicast flow overlay   router for BIER, MUST signal its BIER information as specified in   [RFC8401], [RFC8444], [I-D.ietf-bier-ospfv3-extensions], or   [I-D.ietf-bier-idr-extensions], including a PHP sub-TLV within the   BIER sub-TLV (or TLV in the case of BGP) attached to the BIER-   incapable router's BFR-prefix to request BIER PHP from other BFRs.   The type of the sub-TLV or sub-sub-TLV is TBD, and the length is 0.   For MPLS encapsulation, the BIER-incapable multicast flow overlay   router MAY omit the BIER MPLS Encapsulation sub-TLV, or it MUST set   the Label field in the BIER MPLS Encapsulation sub-TLV to the   Implicit Null Label [RFC3032].   In the case of MPLS encapsulation, if a BFER (which supports BIER but   not a specific BSL) does not support a particular BSL, it MAY   advertise a corresponding BIER MPLS Encapsulation sub-TLV with the   Label field set to the Implicit Null Label to request PHP for that   BSL.  In this scenario, the PHP sub-TLV MUST NOT be included.Zhang                      Expires 7 June 2025                  [Page 4]Internet-Draft                  bier-php                   December 2024   For non-MPLS encapsulation [I-D.ietf-bier-lsr-non-mpls-extensions],   the BIER-incapable multicast flow overlay router MAY omit the BIER   non-MPLS Encapsulation sub-TLV, or it MUST set the BIFT-id field in   the BIER non-MPLS Encapsulation sub-TLV to 0.   Similarly, for non-MPLS encapsulation, if a BFER (which supports BIER   but not a specific BSL) does not support a particular BSL, it MAY   advertise a corresponding BIER non-MPLS Encapsulation sub-TLV but set   the BIFT-id field to 0 to request PHP for that BSL.  In this   scenario, the PHP sub-TLV MUST NOT be included.2.2.  BIRT/BIFT Calculation   If a BFR adheres to Section 6.9 of [RFC8279] for handling BIER-   incapable routers, it MUST treat a router as BIER-incapable for a   specific BSL if the label in the corresponding MPLS Encapsulation   sub-TLV advertised by the router is Implicit Null, or if the BIFT-id   in the corresponding non-MPLS Encapsulation sub-TLV is 0.   Additionally, the router MUST be treated as BIER-incapable for all   BSLs if it advertises a PHP sub-TLV.  Consequently, the router will   not be utilized as a transit BFR for certain or all BSLs.   When the downstream neighbor (whether determined through IGP   calculation or indicated in the BIER Nexthop sub-TLV in the case of   BGP) for a BFR-prefix is the router that advertises the prefix with a   PHP sub-TLV, an Implicit Null Label in its BIER MPLS Encapsulation   sub-TLV, or a BIFT-id of 0 in its BIER non-MPLS Encapsulation sub-   TLV, then, upon the creation or update of the corresponding BIRT or   BIFT entry, the forwarding behavior MUST be that the BIER header is   removed and the payload is forwarded to the downstream router without   the BIER header, either directly or over any type of tunnel.3.  Security Considerations   This specification does not introduce additional security concerns   beyond those already discussed in BIER architecture [RFC8279] and   BIER signaling extensions to OSPF [RFC8444], IS-IS [RFC8401] and BGP   [I-D.ietf-bier-idr-extensions].4.  Operational Considerations   BIER PHP can only be used when the conditions specified in Section 2   are met.  The BIER OAM functionality is not available on the BIER-   incapable flow overlay routers, but using PHP when the conditions are   met is simpler than the alternative of using BIER to send to some   whereas using non-BIER tunnels to send to other flow overlay routers.Zhang                      Expires 7 June 2025                  [Page 5]Internet-Draft                  bier-php                   December 2024   [RFC8279] states that when the BIER header is decapsulated, by   default its Time to Live (TTL) value is not inherited by the payload.   That means in the PHP case, the payload's TTL will be decremented   once more than in the non-PHP case.5.  IANA Considerations   This document requests a new sub-sub-TLV type value from the "Sub-   sub-TLVs for BIER Info Sub-TLV" registry within the "IS-IS TLV   Codepoints" registry:        Type    Name        ----    ----        TBD     BIER PHP Request   This document requests a new sub-TLV type value from the OSPFv2   Extended Prefix TLV Sub-TLV registry:        Type    Name        ----    ----        TBD     BIER PHP Request   This document requests a new sub-TLV type value from the OSPFv3   Extended LSA Sub-TLVs registry:        Type    Name                 L2BM        ----    ----                 ----        TBD     BIER PHP Request     X   This document requests a new sub-TLV type value from the BGP BIER TLV   sub-TLV Types registry requested in [I-D.ietf-bier-idr-extensions]:        Type    Name        ----    ----        TBD     BIER PHP Request6.  Acknowledgements   The author wants to thank Eric Rosen and Antonie Przygienda for their   review, comments and suggestions.  The author also wants to thank   Senthil Dhanaraj for the suggestion of requesting PHP if a BFER does   not support certain BSL.7.  References7.1.  Normative ReferencesZhang                      Expires 7 June 2025                  [Page 6]Internet-Draft                  bier-php                   December 2024   [I-D.ietf-bier-idr-extensions]              Xu, X., Chen, M., Patel, K., Wijnands, I., Przygienda, T.,              and Z. J. Zhang, "BGP Extensions for BIER", Work in              Progress, Internet-Draft, draft-ietf-bier-idr-extensions-              15, 22 November 2024,              <https://datatracker.ietf.org/doc/html/draft-ietf-bier-              idr-extensions-15>.   [I-D.ietf-bier-lsr-non-mpls-extensions]              Dhanaraj, S., Yan, G., Wijnands, I., Psenak, P., Zhang, Z.              J., and J. Xie, "LSR Extensions for BIER non-MPLS              Encapsulation", Work in Progress, Internet-Draft, draft-              ietf-bier-lsr-non-mpls-extensions-03, 7 February 2024,              <https://datatracker.ietf.org/doc/html/draft-ietf-bier-              lsr-non-mpls-extensions-03>.   [I-D.ietf-bier-ospfv3-extensions]              Psenak, P., Nainar, N. K., and I. Wijnands, "OSPFv3              Extensions for BIER", Work in Progress, Internet-Draft,              draft-ietf-bier-ospfv3-extensions-07, 1 December 2022,              <https://datatracker.ietf.org/doc/html/draft-ietf-bier-              ospfv3-extensions-07>.   [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>.   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,              <https://www.rfc-editor.org/info/rfc3032>.   [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>.   [RFC8296]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,              Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation              for Bit Index Explicit Replication (BIER) in MPLS and Non-              MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January              2018, <https://www.rfc-editor.org/info/rfc8296>.Zhang                      Expires 7 June 2025                  [Page 7]Internet-Draft                  bier-php                   December 2024   [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>.   [RFC8556]  Rosen, E., Ed., Sivakumar, M., Przygienda, T., Aldrin, S.,              and A. Dolganow, "Multicast VPN Using Bit Index Explicit              Replication (BIER)", RFC 8556, DOI 10.17487/RFC8556, April              2019, <https://www.rfc-editor.org/info/rfc8556>.   [RFC9573]  Zhang, Z., Rosen, E., Lin, W., Li, Z., and IJ. Wijnands,              "MVPN/EVPN Tunnel Aggregation with Common Labels",              RFC 9573, DOI 10.17487/RFC9573, May 2024,              <https://www.rfc-editor.org/info/rfc9573>.   [RFC9624]  Zhang, Z., Przygienda, T., Sajassi, A., and J. Rabadan,              "EVPN Broadcast, Unknown Unicast, or Multicast (BUM) Using              Bit Index Explicit Replication (BIER)", RFC 9624,              DOI 10.17487/RFC9624, August 2024,              <https://www.rfc-editor.org/info/rfc9624>.7.2.  Informative References   [I-D.ietf-bess-evpn-virtual-hub]              Patel, K., Sajassi, A., Drake, J., Zhang, Z. J., and W.              Henderickx, "Virtual Hub-and-Spoke in BGP EVPNs", Work in              Progress, Internet-Draft, draft-ietf-bess-evpn-virtual-              hub-00, 26 January 2020,              <https://datatracker.ietf.org/doc/html/draft-ietf-bess-              evpn-virtual-hub-00>.   [RFC6513]  Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/              BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February              2012, <https://www.rfc-editor.org/info/rfc6513>.   [RFC6514]  Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP              Encodings and Procedures for Multicast in MPLS/BGP IP              VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,              <https://www.rfc-editor.org/info/rfc6514>.Zhang                      Expires 7 June 2025                  [Page 8]Internet-Draft                  bier-php                   December 2024   [RFC7024]  Jeng, H., Uttaro, J., Jalil, L., Decraene, B., Rekhter,              Y., and R. Aggarwal, "Virtual Hub-and-Spoke in BGP/MPLS              VPNs", RFC 7024, DOI 10.17487/RFC7024, October 2013,              <https://www.rfc-editor.org/info/rfc7024>.   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February              2015, <https://www.rfc-editor.org/info/rfc7432>.   [RFC9574]  Rabadan, J., Ed., Sathappan, S., Lin, W., Katiyar, M., and              A. Sajassi, "Optimized Ingress Replication Solution for              Ethernet VPNs (EVPNs)", RFC 9574, DOI 10.17487/RFC9574,              May 2024, <https://www.rfc-editor.org/info/rfc9574>.Author's Address   Zhaohui Zhang   Juniper Networks   Email: zzhang@juniper.netZhang                      Expires 7 June 2025                  [Page 9]