BIER support via ISIS
draft-ietf-bier-isis-extensions-06

Internet Engineering Task Force                         L. Ginsberg, Ed.
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                           A. Przygienda
Expires: April 25, 2018                                 Juniper Networks
                                                               S. Aldrin
                                                                  Google
                                                                J. Zhang
                                                  Juniper Networks, Inc.
                                                        October 22, 2017

                         BIER support via ISIS
                   draft-ietf-bier-isis-extensions-06

Abstract

   Specification of an ISIS extension to support BIER domains and sub-
   domains.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119] .

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
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   This Internet-Draft will expire on April 25, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   (https://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Concepts  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  BIER Domains and Sub-Domains  . . . . . . . . . . . . . .   4
     4.2.  Advertising BIER Information  . . . . . . . . . . . . . .   5
   5.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Multi Topology and Sub-Domain . . . . . . . . . . . . . .   5
     5.2.  Encapsulation . . . . . . . . . . . . . . . . . . . . . .   5
     5.3.  BIER Algorithm  . . . . . . . . . . . . . . . . . . . . .   5
     5.4.  Label advertisements for MPLS Encapsulation . . . . . . .   6
     5.5.  BFR-id Advertisements . . . . . . . . . . . . . . . . . .   6
     5.6.  Reporting Misconfiguration  . . . . . . . . . . . . . . .   6
     5.7.  Flooding Reduction  . . . . . . . . . . . . . . . . . . .   6
   6.  Packet Formats  . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  BIER Info sub-TLV . . . . . . . . . . . . . . . . . . . .   6
     6.2.  BIER MPLS Encapsulation sub-sub-TLV . . . . . . . . . . .   7
     6.3.  Optional BIER sub-domain BSL conversion sub-sub-TLV . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Bit Index Explicit Replication (BIER)
   [I-D.draft-ietf-bier-architecture-08] defines an architecture where
   all intended multicast receivers are encoded as bitmask in the
   Multicast packet header within different encapsulations such as
   [I-D.draft-ietf-bier-mpls-encapsulation-10].  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.

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   This document presents necessary extensions to the currently deployed
   ISIS for IP [RFC1195] protocol to support distribution of information
   necessary for operation of BIER domains and sub-domains.  This
   document defines a new TLV to be advertised by every router
   participating in BIER signaling.

2.  Terminology

   Some of the terminology specified in
   [I-D.draft-ietf-bier-architecture-08] 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 BFER's).

   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 BM 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 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 sub-domain:  A further distinction within a BIER domain
      identified by its unique sub-domain identifier.  A BIER sub-domain
      can support multiple BitString Lengths.

   BFR-id:  An optional, unique identifier for a BFR within a BIER sub-
      domain.

   Invalid BFR-id:  Unassigned BFR-id.  The special value 0 is reserved
      for this purpose.

   BAR  BIER Algorithm.  Algorithm used to calculate unicast nexthops

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3.  IANA Considerations

   This document adds the following new sub-TLV to the registry of sub-
   TLVs for TLVs 235, 237 [RFC5120] and TLVs 135,236
   [RFC5305],[RFC5308].

   Value: 32 (suggested - to be assigned by IANA)

   Name: BIER Info

   This document also introduces a new registry for sub-sub-TLVs for the
   BIER Info sub-TLV added above.  The registration policy is Expert
   Review as defined in [RFC8126].  This registry is part of the "IS-IS
   TLV Codepoints" registry.  The name of the registry is "sub-sub-TLVs
   for BIER Info sub-TLV".  The defined values are:

     Type    Name
     ----    ----
     1       BIER MPLS Encapsulation
     3       BIER sub-domain BSL conversion

4.  Concepts

4.1.  BIER Domains and Sub-Domains

   An ISIS signalled BIER domain is aligned with the scope of
   distribution of BFR-prefixes that identify the BFRs within ISIS.
   ISIS acts in such a case as the supporting BIER underlay.

   Within such a domain, the extensions defined in this document
   advertise BIER information for one or more BIER sub-domains.  Each
   sub-domain is uniquely identified by a subdomain-id.  Each subdomain
   is associated with a single ISIS topology [RFC5120], which may be any
   of the topologies supported by ISIS.  Local configuration controls
   which <MT,SD> pairs are supported by a router.  The mapping of sub-
   domains to topologies MUST be consistent within a BIER flooding
   domain.

   Each BIER sub-domain has as its unique attributes the encapsulation
   used and the type of tree it is using to forward BIER frames
   (currently always SPF).  Additionally, per supported bitstring length
   in the sub-domain, each router will advertise the necessary label
   ranges to support it.

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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.  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 is present N flag MUST be
      set.  [RFC7794]

   o  BIER sub-TLVs MUST be included when a prefix reachability
      advertisement is leaked between levels.

5.  Procedures

5.1.  Multi Topology and Sub-Domain

   A given sub-domain is supported within one and only one topology.
   All routers in the flooding scope of the BIER sub-TLVs MUST advertise
   the same sub-domain within the same multi-topology.  A router
   receiving an <MT,SD> advertisement which does not match the locally
   configured pair MUST report a misconfiguration of the received <MT,
   SD> pair.  All received BIER advertisements associated with the
   conflicting <MT, SD> pair MUST be ignored.

5.2.  Encapsulation

   All routers in the flooding scope of the BIER TLVs MUST advertise the
   same encapsulation for a given <MT,SD>.  A router discovering
   encapsulation advertised that is different from its own MUST report a
   misconfiguration of a specific <MT,SD>.  All received BIER
   advertisements associated with the conflicting <MT, SD> pair MUST be
   ignored.

5.3.  BIER Algorithm

   All routers in the flooding scope of the BIER TLVs MUST advertise a
   supported algorithm for a given <MT,SD>.  The specified algorithm is
   used when calculating the optimal path.  Currently only the default
   algorithm "SPF" is defined - which has a reserved value of 0.  The
   supported algorithm MUST be consistent for all routers supporting a
   given <MT,SD>.  A router receiving an <MT,SD> advertisement with a
   BAR which does not match the locally configured value MUST report a
   misconfiguration of the received <MT, SD> pair.  All received BIER

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   advertisements associated with the conflicting <MT, SD> pair MUST be
   ignored.

5.4.  Label advertisements for MPLS Encapsulation

   A router that desires to participate in <MT,SD> MUST advertise for
   each bitstring length it supports in <MT,SD> a label range size that
   guarantees to cover the maximum BFR-id injected into <MT,SD> (which
   implies a certain maximum set id per bitstring length as described in
   [I-D.draft-ietf-bier-architecture-08]).  Any router that violates
   this condition MUST be excluded from BIER BFTs for <MT,SD>.

5.5.  BFR-id Advertisements

   Each BFER/BFIR MAY advertise with its TLV<MT,SD> the BFR-id that it
   has administratively chosen.  A valid BFR-id MUST be unique within
   the flooding scope of the BIER advertisments.  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>.

5.6.  Reporting Misconfiguration

   Whenever an advertisement is received which violates any of the
   constraints defined in this document the receiving router MUST report
   the misconfiguration.  Such reports SHOULD be dampened to avoid
   excessive logging output.

5.7.  Flooding Reduction

   BIER domain information SHOULD change infrequently.  Frequent changes
   will increase the number of Link State PDU (LSP) updates and
   negatively impact performance in the network.

6.  Packet Formats

   All ISIS BIER information is carried within the TLVs 235, 237
   [RFC5120] or TLVs 135 [RFC5305], or TLV 236 [RFC5308].

6.1.  BIER Info sub-TLV

   This sub-TLV carries the information for the BIER sub-domains that
   the router participates in as BFR.  This sub-TLV MAY appear multiple
   times in a given prefix-reachability TLV - once for each sub-domain
   supported in the associated topology.

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   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         | subdomain-id  |   BFR-id                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  sub-sub-TLVs (variable)                                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:  as indicated in IANA section.

   Length:  variable

   BAR  BIER Algorithm. 0 is the only supported value defined in this
      document.  Other values may be defined in the future. 8 bits

   subdomain-id:  Unique value identifying the BIER sub-domain. 1 octet

   BFR-id:  A 2 octet field encoding the BFR-id, as documented in
      [I-D.draft-ietf-bier-architecture-08].  If no BFR-id has been
      assigned this field is set to the invalid BFR-id.

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.

   On violation of any of the following conditions, the receiving router
   MUST ignore the encapsulating BIER Info sub-TLV.

   o  Label ranges in multiple sub-sub-TLV MUST NOT overlap.

   o  Bitstring lengths in multiple sub-sub-TLVs MUST NOT be identical.

   o  The sub-sub-TLV MUST include the required bitstring lengths
      encoded in precisely the same way as in
      [I-D.draft-ietf-bier-mpls-encapsulation-10].

   o  The label range size MUST be greater than 0.

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   o  All labels in the range MUST represent valid label values

        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      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Lbl Range Size|BS Len |                    Label              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:  value of 1 indicating MPLS encapsulation.

   Length:  4

   Local BitString Length (BS Len):  Encoded bitstring length as per [I-
      D.draft-ietf-bier-mpls-encapsulation-10]. 4 bits.

   Label Range Size:  Number of labels in the range used on
      encapsulation for this BIER sub-domain for this bitstring length,
      1 octet.  The size of the label range is determined by the number
      of Set Identifiers (SI) (section 1 of [I-D.ietf-bier-
      architecture]) that are used in the network.  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.

   Label:  First label of the range, 20 bits.  The labels are as defined
      in [I-D.draft-ietf-bier-mpls-encapsulation-10].

6.3.  Optional BIER sub-domain BSL conversion sub-sub-TLV

   This sub-sub-TLV indicates whether the BFR is capable of imposing a
   different Bit String Length (BSL) than the one it received in a BIER
   encapsulated packet.  Such a capability may allow future, advanced
   tree types which ensure simple migration procedures from one BSL to
   another in a given <MT,SD> or prevent stable blackholes in scenarios
   where not all routers support the same set of BSLs in a given
   <MT,SD>.  Conversions are supported only between the set of BSLs
   advertised as supported by the router.  It is carried within the BIER
   Info sub-TLV (Section 6.1).  This sub-sub-TLV is optional and its
   absence indicates that the router is NOT capable of imposing
   different BSLs but will always forward the packet with the BSL
   unchanged.  This sub-sub-TLV MAY occur at most once in a given BIER
   info sub-TLV.  If multiple occurences of this sub-sub-TLV are
   received in a given BIER info sub-TLV the encapsulating sub-TLV MUST
   be ignored.

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         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      |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:  value of 3 indicating BIER sub-domain BSL Conversion

   Length:  0

7.  Security Considerations

   Implementations must assure that malformed TLV and Sub-TLV
   permutations do not result in errors which cause hard protocol
   failures.

8.  Acknowledgements

   The RFC is aligned with the
   [I-D.draft-ietf-bier-ospf-bier-extensions-08] draft 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.

9.  References

9.1.  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>.

   [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>.

   [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>.

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   [RFC5308]  Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
              DOI 10.17487/RFC5308, October 2008,
              <https://www.rfc-editor.org/info/rfc5308>.

   [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>.

9.2.  Informative References

   [I-D.draft-ietf-bier-architecture-08]
              Wijnands et al., IJ., "Stateless Multicast using Bit Index
              Explicit Replication Architecture", internet-draft draft-
              ietf-bier-architecture-08.txt, Sep 2017.

   [I-D.draft-ietf-bier-mpls-encapsulation-10]
              Wijnands et al., IJ., "Bit Index Explicit Replication
              using MPLS encapsulation", internet-draft draft-ietf-bier-
              mpls-encapsulation-10.txt, Sep 2017.

   [I-D.draft-ietf-bier-ospf-bier-extensions-08]
              Psenak et al., P., "OSPF Extension for Bit Index Explicit
              Replication", internet-draft draft-ietf-bier-ospf-bier-
              extensions-08.txt, Oct 2017.

   [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>.

Authors' Addresses

   Les Ginsberg (editor)
   Cisco Systems
   510 McCarthy Blvd.
   Milpitas, CA  95035
   USA

   Email: ginsberg@cisco.com

   Tony Przygienda
   Juniper Networks

   Email: prz@juniper.net

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   Sam Aldrin
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA
   USA

   Email: aldrin.ietf@gmail.com

   Jeffrey (Zhaohui) Zhang
   Juniper Networks, Inc.
   10 Technology Park Drive
   Westford, MA  01886
   USA

   Email: zzhang@juniper.net

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