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rfc:rfc8401

Internet Engineering Task Force (IETF) L. Ginsberg, Ed. Request for Comments: 8401 Cisco Systems Category: Standards Track A. Przygienda ISSN: 2070-1721 Juniper Networks

                                                             S. Aldrin
                                                                Google
                                                              J. Zhang
                                                Juniper Networks, Inc.
                                                             June 2018
      Bit Index Explicit Replication (BIER) Support via IS-IS

Abstract

 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 in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://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 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.

Ginsberg, et al. Standards Track [Page 1] RFC 8401 BIER Support via IS-IS June 2018

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
 2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
 3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
 4.  Concepts  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.1.  BIER Domains and Subdomains . . . . . . . . . . . . . . .   5
   4.2.  Advertising BIER Information  . . . . . . . . . . . . . .   5
 5.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.1.  Multi-Topology and Subdomain  . . . . . . . . . . . . . .   5
   5.2.  BFR-id Advertisements . . . . . . . . . . . . . . . . . .   6
   5.3.  Logging Misconfiguration  . . . . . . . . . . . . . . . .   6
   5.4.  Flooding Reduction  . . . . . . . . . . . . . . . . . . .   6
 6.  Packet Formats  . . . . . . . . . . . . . . . . . . . . . . .   7
   6.1.  BIER Info Sub-TLV . . . . . . . . . . . . . . . . . . . .   7
   6.2.  BIER MPLS Encapsulation Sub-sub-TLV . . . . . . . . . . .   8
 7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
 8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
   8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1. 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 2018

2. 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 2018

2.1. 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 in
 BCP 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: Reserved

Ginsberg, et al. Standards Track [Page 4] RFC 8401 BIER Support via IS-IS June 2018

4. Concepts

4.1. 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. Procedures

5.1. 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 pair

Ginsberg, 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 2018

6. 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 in Section 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 2018

8. References

8.1. 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 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>.

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 2018

Authors' 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.net

Ginsberg, et al. Standards Track [Page 12]

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