IS-IS Extensions for BIER-TE

Internet-Draft	ISIS for BIER-TE	April 2023
Chen, et al.	Expires 29 October 2023	[Page]

Abstract

This document describes IS-IS extensions for distributing the BitPositions configured on a Bit-Forwarding Router (BFR) in a "Bit Index Explicit Replication Traffic Engineering" (BIER-TE) domain.¶

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1. Introduction

[RFC9262] introduces Bit Index Explicit Replication (BIER) Traffic/Tree Engineering (BIER-TE). It is an architecture for per-packet stateless explicit point to multipoint (P2MP) multicast path/tree. There are three types of BitPositions (BPs) in a BIER-TE domain: link BitPosition (BP), routed BP and localdecap BP. A link BP is a BP configured on a link from Bit-Forwarding Router (BFR) X to BFR Y for a forward connected adjacency from X to Y. A routed BP is a BP configured on BFR X for a forward routed adjacency from X to a remote BFR Z not directly connected to X. A localdecap BP is a BP configured on a BFR.¶

[RFC8401] describes IS-IS Extensions for distributing the BFR identifier (BFR-id) configured on a BFR. This document specifies IS-IS extensions for distributing the BitPositions configured a BFR in a BIER-TE domain. The BitPositions distributed may be used by a BFR as a Point of Local Repair (PLR) for Fast-ReRoute (FRR).¶

2. Extensions to IS-IS

This section describes protocol extensions to IS-IS for distributing the BitPositions configured on a BFR in a BIER-TE domain.¶

2.1. Link BitPosition

An Extended IS Reachability TLV (Type 22) defined in [RFC5305] may contain Sub-TLVs (such as those for TE) that apply to a link/interface to a neighbor. To encode multiple links or interfaces to neighbors, the structure inside TLV is repeated.¶

MT Intermediate Systems TLV (Type 222) defined in [RFC5120] may contain Sub-TLVs (such as those for TE) that apply to a link/interface. It is aligned with Extended IS Reachability TLV (Type 22) beside an additional two bytes in front at the beginning of the TLV for MT-ID.¶

Link-BP Sub-TLV of the following format is defined and used in Extended IS Reachability TLV (Type 22) and/or MT Intermediate Systems TLV (Type 222) to advertise a link BP.¶

    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 (TBD1)  |    Length     | sub-domain-id |      BAR      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPA      |         BitPosition           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     DisEndBitPosition         |    Sub-Sub-TLVs (variable)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: Link-BP Sub-TLV

Type:: TBD1 is to be assigned by IANA.¶
Length:: Variable, dependent on Sub-Sub-TLVs.¶
sub-domain-id:: Unique value identifying a BIER-TE sub-domain.¶
BAR:: Single-octet BIER Algorithm used to calculate underlay paths to reach other BFRs. Values are allocated from the "BIER Algorithm" registry defined in [RFC8401].¶
IPA:: Single-octet IGP Algorithm used to either modify, enhance, or replace the calculation of underlay paths to reach other BFRs as defined by the BAR value. Values are defined in the "IGP Algorithm Types" registry.¶
BitPosition:: A 2-octet field encoding the BitPosition locally configured on the link/interface to an Intermediate System neighbor.¶
DisEndBitPosition:: A 2-octet field encoding the BitPosition of the connection on the designated Intermediate Systems (Dis) end. This field exists when the neighbor is a pseudonode. If the neighbor is not a pseudonode, this field MUST NOT exist. The DisEndBitPosition may be configured on the link/interface to a transit network (i.e., broadcast link or say LAN) as described in [I-D.chen-bier-te-lan].¶

No Sub-Sub-TLVs are currently defined.¶

2.2. Routed and Localdecap BitPositions

A TLV, called Node BPs TLV, is defined. The TLV contains Sub-TLVs. Two types of Sub-TLVs are defined. One is for a Routed BitPosition and the other for a Localdecap BitPosition. The Node BPs TLV has the following format:¶

    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 (TBD2)   |    Length     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Sub-TLVs                           ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Node BPs TLV

Type:: TBD2 is to be assigned by IANA.¶
Length:: Variable.¶
Sub-TLVs:: Sub-TLVs containing the Routed BitPositions and Localdecap BitPosition configured on a BFR.¶

The Routed-BP Sub-TLV has the following format:¶

    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 (1)    |    Length(8)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | sub-domain-id |     MT-ID     |      BAR      |    IPA        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         BitPosition           |             BFR-id            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: Routed-BP Sub-TLV

Type:: 1 is the type for routed BP.¶
Length:: It is 8.¶
BitPosition:: A 2-octet field encoding the BitPosition configured on a BFR for a forward routed adjacency to a remote BFR.¶
BFR-id:: A 2-octet field encoding the BFR-id of the remote BFR.¶
sub-domain-id, MT-ID, BAR and IPA:: They are the same as those described in Section 2.1.¶

The Localdecap-BP Sub-TLV has the following format:¶

    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 (2)    |   Length(6)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | sub-domain-id |     MT-ID     |      BAR      |    IPA        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         BitPosition           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: Localdecap-BP Sub-TLV

Type:: 2 is the type for localdecap BP.¶
Length:: It is 6.¶
BitPosition:: A 2-octet field encoding the localdecap BitPosition configured on a BFR.¶
sub-domain-id, MT-ID, BAR and IPA:: They are the same as those described Section 2.1.¶

3. Security Considerations

Protocol extensions defined in this document do not affect the IS-IS security.¶

4. IANA Considerations

Under "IS-IS Sub-TLVs for TLVs Advertising Neighbor Information" registry, IANA is requested to assign a new Sub-TLV Type for Link BP as follows:¶

  +=======+=============+==+==+==+===+===+===+=============+
  | Type  |Description  |22|23|25|141|222|223|reference    |
  +=======+=============+==+==+==+===+===+===+=============+
  | TBD1  |  Link BP    |y |y |n | n | y | y |This document|
  +-------+-------------+--+--+--+---+---+---+-------------+

IANA is requested to make a new allocation in the "IS-IS TLV Codepoint Registry" under the registry name "IS-IS TLV Codepoints" as follows:¶

  +==============+===================+=====================+
  |  TLV Type    |      TLV Name     |    reference        |
  +==============+===================+=====================+
  |  TBD2        | Node BPs ID       |    This document    |
  +--------------+-------------------+---------------------+
  Note that TBD2 is less than 255.

IANA is requested to create a new sub-registry "Sub-TLVs for TLV type TBD2 (Node BPs TLV)" under the IANA IS-IS TLV Codepoints as follows:¶

  +==============+===================+=====================+
  |     Type     |      Name         |    reference        |
  +==============+===================+=====================+
  |     0        |                Reserved                 |
  +--------------+-------------------+---------------------+
  |     1        |   Link BP         |    This document    |
  +--------------+-------------------+---------------------+
  |     2        |   Localdecap BP   |    This document    |
  +--------------+-------------------+---------------------+
  |     3 - 255  |                Unassigned               |
  +--------------+-------------------+---------------------+

5. References

5.1. 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, <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>.
[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>.
[RFC9262]: Eckert, T., Ed., Menth, M., and G. Cauchie, "Tree Engineering for Bit Index Explicit Replication (BIER-TE)", RFC 9262, DOI 10.17487/RFC9262, October 2022, <https://www.rfc-editor.org/info/rfc9262>.

5.2. Informative References

[I-D.chen-bier-te-lan]: Chen, H., McBride, M., Wang, A., Mishra, G. S., Liu, L., and X. Liu, "BIER-TE for Broadcast Link", Work in Progress, Internet-Draft, draft-chen-bier-te-lan-06, 9 March 2023, <https://datatracker.ietf.org/doc/html/draft-chen-bier-te-lan-06>.
[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>.