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Internet Engineering Task Force (IETF)                  L. Ginsberg, Ed.Request for Comments: 8401                                 Cisco SystemsCategory: Standards Track                                  A. PrzygiendaISSN: 2070-1721                                         Juniper Networks                                                               S. Aldrin                                                                  Google                                                                J. Zhang                                                  Juniper Networks, Inc.                                                               June 2018Bit Index Explicit Replication (BIER) Support via IS-ISAbstract   This document defines IS-IS extensions to support multicast   forwarding using the Bit Index Explicit Replication (BIER)   architecture.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8401.Copyright Notice   Copyright (c) 2018 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Ginsberg, et al.             Standards Track                    [Page 1]

RFC 8401                 BIER Support via IS-IS                June 2018Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .32.1.  Requirements Language . . . . . . . . . . . . . . . . . .43.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .44.  Concepts  . . . . . . . . . . . . . . . . . . . . . . . . . .54.1.  BIER Domains and Subdomains . . . . . . . . . . . . . . .54.2.  Advertising BIER Information  . . . . . . . . . . . . . .55.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .55.1.  Multi-Topology and Subdomain  . . . . . . . . . . . . . .55.2.  BFR-id Advertisements . . . . . . . . . . . . . . . . . .65.3.  Logging Misconfiguration  . . . . . . . . . . . . . . . .65.4.  Flooding Reduction  . . . . . . . . . . . . . . . . . . .66.  Packet Formats  . . . . . . . . . . . . . . . . . . . . . . .76.1.  BIER Info Sub-TLV . . . . . . . . . . . . . . . . . . . .76.2.  BIER MPLS Encapsulation Sub-sub-TLV . . . . . . . . . . .87.  Security Considerations . . . . . . . . . . . . . . . . . . .98.  References  . . . . . . . . . . . . . . . . . . . . . . . . .108.1.  Normative References  . . . . . . . . . . . . . . . . . .108.2.  Informative References  . . . . . . . . . . . . . . . . .11   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .11   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .121.  Introduction   Bit Index Explicit Replication (BIER) [RFC8279] defines an   architecture where all intended multicast receivers are encoded as a   bitmask in the multicast packet header within different   encapsulations such as described in [RFC8296].  A router that   receives such a packet will forward the packet based on the bit   position in the packet header towards the receiver(s) following a   precomputed tree for each of the bits in the packet.  Each receiver   is represented by a unique bit in the bitmask.   This document presents necessary extensions to the currently deployed   IS-IS for IP [RFC1195] to support distribution of information   necessary for operation of BIER domains and subdomains.  This   document defines a new TLV to be advertised by every router   participating in BIER signaling.   This document defines support for MPLS encapsulation as specified in   [RFC8296].  Support for other encapsulation types and the use of   multiple encapsulation types are outside the scope of this document.Ginsberg, et al.             Standards Track                    [Page 2]

RFC 8401                 BIER Support via IS-IS                June 20182.  Terminology   Some of the terminology specified in [RFC8279] is replicated here and   extended by necessary definitions:   BIER:  Bit Index Explicit Replication.  The overall architecture of      forwarding multicast using a bit position.   BIER-OL:  BIER Overlay Signaling.  The method for the BFIR to learn      about BFERs.   BFR:  Bit Forwarding Router.  A router that participates in Bit Index      Multipoint Forwarding.  A BFR is identified by a unique BFR-prefix      in a BIER domain.   BFIR:  Bit Forwarding Ingress Router.  The ingress border router that      inserts the BitString into the packet.  Each BFIR must have a      valid BFR-id assigned.   BFER:  Bit Forwarding Egress Router.  A router that participates in      Bit Index Forwarding as a leaf.  Each BFER must be a BFR.  Each      BFER must have a valid BFR-id assigned.   BFT:  Bit Forwarding Tree used to reach all BFERs in a domain.   BIER subdomain:  A further distinction within a BIER domain      identified by its unique subdomain identifier.  A BIER subdomain      can support multiple BitString Lengths.   BFR-id:  An optional, unique identifier for a BFR within a BIER      subdomain.   Invalid BFR-id:  Unassigned BFR-id.  The special value 0 is reserved      for this purpose.   BAR:  BIER Algorithm.  Used to calculate underlay next hops.   IPA:  IGP Algorithm.  May be used to modify, enhance, or replace the      calculation of underlay paths as defined by the BAR value.   SPF:  Shortest Path First routing calculation based on the IGP link      metric.Ginsberg, et al.             Standards Track                    [Page 3]

RFC 8401                 BIER Support via IS-IS                June 20182.1.  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 inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.3.  IANA Considerations   This document adds the following entry to the "Sub-TLVs for TLVs 135,   235, 236, and 237" registry.   Value: 32   Name: BIER Info   This document also introduces a new registry for sub-sub-TLVs for the   BIER Info sub-TLV.  The registration policy is Expert Review as   defined in [RFC8126].  The "Sub-sub-TLVs for BIER Info Sub-TLV" has   been created within the "IS-IS TLV Codepoints" registry.  The defined   value is as follows:     Type    Name     ----    ----     1       BIER MPLS Encapsulation   IANA has created the "BIER Algorithms" registry within the "Bit Index   Explicit Replication (BIER)" registry.  The registration policies   [RFC8126] for this registry are:      "Standards Action" for values 0-127      "Specification Required" for values 128-239      "Experimental Use" for values 240-254   The initial values in the "BIER Algorithms" registry are:      0: No BIER-specific algorithm is used      255: ReservedGinsberg, et al.             Standards Track                    [Page 4]

RFC 8401                 BIER Support via IS-IS                June 20184.  Concepts4.1.  BIER Domains and Subdomains   An IS-IS-signaled BIER domain is aligned with the scope of   distribution of BFR-prefixes that identify the BFRs within IS-IS.  In   such a case, IS-IS acts as the supporting BIER underlay.   Within such a domain, the extensions defined in this document   advertise BIER information for one or more BIER subdomains.  Each   subdomain is uniquely identified by a subdomain-id (SD).  Each   subdomain is associated with a single IS-IS topology (MT) [RFC5120],   which may be any of the topologies supported by IS-IS.  Local   configuration controls which <MT,SD> pairs are supported by a router.   The mapping of subdomains to topologies MUST be consistent within the   IS-IS flooding domain used to advertise BIER information.   Each BIER subdomain has as its unique attributes the encapsulation   used and the type of tree it uses to forward BIER frames (currently   always SPF).  Additionally, per supported BitString length in the   subdomain, each router will advertise the necessary label ranges to   support it.4.2.  Advertising BIER Information   BIER information advertisements are associated with a new sub-TLV in   the extended reachability TLVs.  BIER information is always   associated with a host prefix, which MUST be a node address for the   advertising node.  If this is not the case, the advertisement MUST be   ignored.  Therefore, the following restrictions apply:   o  Prefix length MUST be 32 for an IPv4 prefix or 128 for an IPv6      prefix.   o  When the Prefix Attributes Flags sub-TLV [RFC7794] is present, the      N flag MUST be set and the R flag MUST NOT be set.   o  BIER sub-TLVs MUST be included when a prefix reachability      advertisement is leaked between levels.5.  Procedures5.1.  Multi-Topology and Subdomain   A given subdomain is supported within one and only one topology.  All   routers in the flooding scope of the BIER sub-TLVs MUST advertise the   same subdomain within the same multi-topology.  A router receiving an   <MT,SD> advertisement that does not match the locally configured pairGinsberg, et al.             Standards Track                    [Page 5]

RFC 8401                 BIER Support via IS-IS                June 2018   MUST report a misconfiguration of the received <MT,SD> pair.  All   received BIER advertisements associated with the conflicting <MT,SD>   pair MUST be ignored.  Note that in the presence of such a   misconfiguration, this will lead to partitioning of the subdomain.   Example:   The following combination of advertisements are valid: <0,0> <0,1>,   and <2,2>.   The following combination of advertisements are invalid: <0,0> <0,1>,   and <2,0>.  Advertisements associated with <0,0> and <2,0> must be   ignored.5.2.  BFR-id Advertisements   If a BFER/BFIR is configured with a BFR-id, then it advertises this   value in its BIER advertisements.  If no BFR-id is configured, then   the value "Invalid BFR-id" is advertised.  A valid BFR-id MUST be   unique within the flooding scope of the BIER advertisements.  All   BFERs/BFIRs MUST detect advertisement of duplicate valid BFR-IDs for   a given <MT,SD>.  When such duplication is detected, all of the   routers advertising duplicates MUST be treated as if they did not   advertise a valid BFR-id.  This implies they cannot act as BFER or   BFIR in that <MT,SD>.5.3.  Logging Misconfiguration   Whenever an advertisement is received that violates any of the   constraints defined in this document, the receiving router MUST   support logging this occurrence.  Logging SHOULD be dampened to avoid   excessive output.5.4.  Flooding Reduction   It is expected that changes in the BIER domain information that is   advertised by IS-IS occur infrequently.  If this expectation is not   met for an extended period of time (more than a few seconds of   burstiness), changes will increase the number of Link State PDU (LSP)   updates and negatively impact performance in the network.   Implementations SHOULD protect against this possibility by, for   example, dampening updates if they occur over an extended period of   time.Ginsberg, et al.             Standards Track                    [Page 6]

RFC 8401                 BIER Support via IS-IS                June 20186.  Packet Formats   All IS-IS BIER information is carried within the TLVs 235, 237,   [RFC5120], 135 [RFC5305], or 236 [RFC5308].6.1.  BIER Info Sub-TLV   This sub-TLV carries the information for the BIER subdomains that the   router participates in as a BFR.  This sub-TLV MAY appear multiple   times in a given prefix-reachability TLV -- once for each subdomain   supported in the associated topology.   The sub-TLV advertises a single <MT,SD> combination followed by   optional sub-sub-TLVs as described in the following sections.        0                   1                   2                   3        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       |    Type       |   Length      |       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       |   BAR         |    IPA        | subdomain-id  |       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       |     BFR-id                    |       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       |  sub-sub-TLVs (variable)                                      |       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type:  As indicated in the IANA section.   Length:  Variable   BAR:  BIER Algorithm.  Specifies a BIER-specific algorithm used to      calculate underlay paths to reach BFERs.  Values are allocated      from the "BIER Algorithms" registry. 1 octet.   IPA:  IGP Algorithm.  Specifies an IGP Algorithm to either modify,      enhance, or replace the calculation of underlay paths to reach      BFERs as defined by the BAR value.  Values are from the IGP      Algorithm registry. 1 octet.   subdomain-id:  Unique value identifying the BIER subdomain. 1 octet.   BFR-id:  A 2-octet field encoding the BFR-id, as documented in      [RFC8279].  If no BFR-id has been assigned, the value of this      field is set to "Invalid BFR-id", which is defined as illegal in      [RFC8279].Ginsberg, et al.             Standards Track                    [Page 7]

RFC 8401                 BIER Support via IS-IS                June 2018   The use of non-zero values in either the BAR field or the IPA field   is outside the scope of this document.  If an implementation does not   support the use of non-zero values in these fields but receives a   BIER Info sub-TLV containing non-zero values in these fields, it   SHOULD treat the advertising router as incapable of supporting BIER   (one way of handling incapable routers is documented inSection 6.9   of [RFC8279] and additional methods may be defined in the future).6.2.  BIER MPLS Encapsulation Sub-sub-TLV   This sub-sub-TLV carries the information for the BIER MPLS   encapsulation including the label range for a specific BitString   length for a certain <MT,SD>.  It is advertised within the BIER Info   sub-TLV (Section 6.1).  This sub-sub-TLV MAY appear multiple times   within a single BIER Info sub-TLV.   If the same BitString length is repeated in multiple sub-sub-TLVs   inside the same BIER Info sub-TLV, the BIER Info sub-TLV MUST be   ignored.   Label ranges within all BIER MPLS Encapsulation sub-sub-TLVs across   all BIER Info sub-TLVs advertised by the same BFR MUST NOT overlap.   If overlap is detected, the advertising router MUST be treated as if   it did not advertise any BIER sub-TLVs.   Label values MUST NOT match any of the reserved values defined in   [RFC3032].        0                   1                   2                   3        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       |    Type       |   Length      |       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       |   Max SI      |BS Len |                    Label              |       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Type:  Value of 1 indicating MPLS encapsulation.   Length:  4   Max SI:  Maximum Set Identifier (Section 1 of [RFC8279]) used in the      encapsulation for this BIER subdomain for this BitString length, 1      octet.  Each SI maps to a single label in the label range.  The      first label is for SI=0, the second label is for SI=1, etc.  If      the label associated with the Maximum Set Identifier exceeds the      20-bit range, the sub-sub-TLV MUST be ignored.Ginsberg, et al.             Standards Track                    [Page 8]

RFC 8401                 BIER Support via IS-IS                June 2018   Local BitString Length (BS Len):  Encoded BitString length as per      [RFC8296]. 4 bits.   Label:  First label of the range, 20 bits.  The labels are as defined      in [RFC8296].7.  Security Considerations   Security concerns for IS-IS are addressed in [RFC5304] and [RFC5310].   The Security Considerations section of [RFC8279] discusses the   possibility of performing a Denial-of-Service (DoS) attack by setting   too many bits in the BitString of a BIER-encapsulated packet.   However, this sort of DoS attack cannot be initiated by modifying the   IS-IS BIER advertisements specified in this document.  A BFIR decides   which systems are to receive a BIER-encapsulated packet.  In making   this decision, it is not influenced by the IS-IS control messages.   When creating the encapsulation, the BFIR sets one bit in the   encapsulation for each destination system.  The information in the   IS-IS BIER advertisements is used to construct the forwarding tables   that map each bit in the encapsulation into a set of next hops for   the host that is identified by that bit, but it is not used by the   BFIR to decide which bits to set.  Hence, an attack on the IS-IS   control plane cannot be used to cause this sort of DoS attack.   While a BIER-encapsulated packet is traversing the network, a BFR   that receives a BIER-encapsulated packet with n bits set in its   BitString may have to replicate the packet and forward multiple   copies.  However, a given bit will only be set in one copy of the   packet.  This means that each transmitted replica of a received   packet has fewer bits set (i.e., is targeted to fewer destinations)   than the received packet.  This is an essential property of the BIER-   forwarding process as defined in [RFC8279].  While a failure of this   process might cause a DoS attack (as discussed in the Security   Considerations of [RFC8279]), such a failure cannot be caused by an   attack on the IS-IS control plane.   Further discussion of BIER-specific security considerations can be   found in [RFC8279].Ginsberg, et al.             Standards Track                    [Page 9]

RFC 8401                 BIER Support via IS-IS                June 20188.  References8.1.  Normative References   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and              dual environments",RFC 1195, DOI 10.17487/RFC1195,              December 1990, <https://www.rfc-editor.org/info/rfc1195>.   [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>.   [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>.   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic              Authentication",RFC 5304, DOI 10.17487/RFC5304, October              2008, <https://www.rfc-editor.org/info/rfc5304>.   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic              Engineering",RFC 5305, DOI 10.17487/RFC5305, October              2008, <https://www.rfc-editor.org/info/rfc5305>.   [RFC5308]  Hopps, C., "Routing IPv6 with IS-IS",RFC 5308,              DOI 10.17487/RFC5308, October 2008,              <https://www.rfc-editor.org/info/rfc5308>.   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,              and M. Fanto, "IS-IS Generic Cryptographic              Authentication",RFC 5310, DOI 10.17487/RFC5310, February              2009, <https://www.rfc-editor.org/info/rfc5310>.   [RFC7794]  Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and              U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4              and IPv6 Reachability",RFC 7794, DOI 10.17487/RFC7794,              March 2016, <https://www.rfc-editor.org/info/rfc7794>.Ginsberg, et al.             Standards Track                   [Page 10]

RFC 8401                 BIER Support via IS-IS                June 2018   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC2119 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>.8.2.  Informative References   [OPSFv2BIER]              Psenak, P., Kumar, N., Wijnands, I., Dolganow, A.,              Przygienda, T., Zhang, Z., and S. Aldrin, "OSPFv2              Extensions for BIER", Work in Progress,draft-ietf-bier-ospf-bier-extensions-18, June 2018.   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for              Writing an IANA Considerations Section in RFCs",BCP 26,RFC 8126, DOI 10.17487/RFC8126, June 2017,              <https://www.rfc-editor.org/info/rfc8126>.Acknowledgements   This RFC is aligned with "OSPFv2 Extensions for BIER" [OPSFv2BIER]   document as far as the protocol mechanisms overlap.   Many thanks for comments from (in no particular order) Hannes   Gredler, IJsbrand Wijnands, Peter Psenak, and Chris Bowers.   Special thanks to Eric Rosen.Ginsberg, et al.             Standards Track                   [Page 11]

RFC 8401                 BIER Support via IS-IS                June 2018Authors' Addresses   Les Ginsberg (editor)   Cisco Systems   510 McCarthy Blvd.   Milpitas, CA  95035   United States of America   Email: ginsberg@cisco.com   Tony Przygienda   Juniper Networks   Email: prz@juniper.net   Sam Aldrin   Google   1600 Amphitheatre Parkway   Mountain View, CA   United States of America   Email: aldrin.ietf@gmail.com   Jeffrey (Zhaohui) Zhang   Juniper Networks, Inc.   10 Technology Park Drive   Westford, MA  01886   United States of America   Email: zzhang@juniper.netGinsberg, et al.             Standards Track                   [Page 12]