path: root/doc/rfc/rfc7176.txt

Internet Engineering Task Force (IETF)                   D. Eastlake 3rd
Request for Comments: 7176                                        Huawei
Obsoletes: 6326                                          T. Senevirathne
Category: Standards Track                                          Cisco
ISSN: 2070-1721                                              A. Ghanwani
                                                                    Dell
                                                                 D. Dutt
                                                        Cumulus Networks
                                                             A. Banerjee
                                                        Insieme Networks
                                                                May 2014


   Transparent Interconnection of Lots of Links (TRILL) Use of IS-IS

Abstract

   The IETF Transparent Interconnection of Lots of Links (TRILL)
   protocol provides optimal pair-wise data frame forwarding without
   configuration in multi-hop networks with arbitrary topology and link
   technology; it also provides support for multipathing of both unicast
   and multicast traffic.  This document specifies the data formats and
   code points for the IS-IS extensions to support TRILL.  These data
   formats and code points may also be used by technologies other than
   TRILL.  This document obsoletes RFC 6326.

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 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7176.












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Copyright Notice

   Copyright (c) 2014 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
   (http://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.

Table of Contents

   1. Introduction ....................................................3
      1.1. Conventions Used in This Document ..........................4
   2. TLV and Sub-TLV Extensions to IS-IS for TRILL ...................4
      2.1. Group Address TLV ..........................................5
           2.1.1. Group MAC Address Sub-TLV ...........................5
           2.1.2. Group IPv4 Address Sub-TLV ..........................7
           2.1.3. Group IPv6 Address Sub-TLV ..........................8
           2.1.4. Group Labeled MAC Address Sub-TLV ...................9
           2.1.5. Group Labeled IPv4 Address Sub-TLV .................10
           2.1.6. Group Labeled IPv6 Address Sub-TLV .................11
      2.2. Multi-Topology-Aware Port Capability Sub-TLVs .............12
           2.2.1. Special VLANs and Flags Sub-TLV ....................12
           2.2.2. Enabled-VLANs Sub-TLV ..............................13
           2.2.3. Appointed Forwarders Sub-TLV .......................14
           2.2.4. Port TRILL Version Sub-TLV .........................15
           2.2.5. VLANs Appointed Sub-TLV ............................17
      2.3. Sub-TLVs of the Router Capability and MT-Capability TLVs ..17
           2.3.1. TRILL Version Sub-TLV ..............................18
           2.3.2. Nickname Sub-TLV ...................................19
           2.3.3. Trees Sub-TLV ......................................20
           2.3.4. Tree Identifiers Sub-TLV ...........................20
           2.3.5. Trees Used Identifiers Sub-TLV .....................21
           2.3.6. Interested VLANs and Spanning Tree Roots Sub-TLV ...22
           2.3.7. VLAN Group Sub-TLV .................................24
           2.3.8. Interested Labels and Spanning Tree Roots Sub-TLV ..25
           2.3.9. RBridge Channel Protocols Sub-TLV ..................27
           2.3.10. Affinity Sub-TLV ..................................29
           2.3.11. Label Group Sub-TLV ...............................30
      2.4. MTU Sub-TLV for Extended Reachability and MT-ISN TLVs .....31
      2.5. TRILL Neighbor TLV ........................................31
   3. MTU PDUs .......................................................33



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   4. Use of Existing PDUs and TLVs ..................................35
      4.1. TRILL IIH PDUs ............................................35
      4.2. Area Address ..............................................35
      4.3. Protocols Supported .......................................35
      4.4. Link State PDUs (LSPs) ....................................35
      4.5. Originating LSP Buffer Size ...............................36
   5. IANA Considerations ............................................36
      5.1. TLVs ......................................................36
      5.2. Sub-TLVs ..................................................36
      5.3. PDUs ......................................................38
      5.4. Reserved and Capability Bits ..............................38
      5.5. TRILL Neighbor Record Flags ...............................39
   6. Security Considerations ........................................39
   7. Changes from RFC 6326 ..........................................39
   8. References .....................................................41
      8.1. Normative References ......................................41
      8.2. Informative References ....................................43
   9. Acknowledgements ...............................................44

1.  Introduction

   The IETF Transparent Interconnection of Lots of Links (TRILL)
   protocol [RFC6325] [RFC7177] provides transparent forwarding in
   multi-hop networks with arbitrary topology and link technologies
   using a header with a hop count and link-state routing.  TRILL
   provides optimal pair-wise forwarding without configuration, safe
   forwarding even during periods of temporary loops, and support for
   multipathing of both unicast and multicast traffic.  Intermediate
   Systems (ISs) implementing TRILL are called Routing Bridges
   (RBridges) or TRILL Switches.

   This document, in conjunction with [RFC6165], specifies the data
   formats and code points for the IS-IS [ISO-10589] [RFC1195]
   extensions to support TRILL.  These data formats and code points may
   also be used by technologies other than TRILL.

   This document obsoletes [RFC6326], which generally corresponded to
   the base TRILL protocol [RFC6325].  There has been substantial
   development of TRILL since the publication of those documents.  The
   main changes from [RFC6326] are summarized below, and a full list is
   given in Section 7.

   1.  Added multicast group announcements by IPv4 and IPv6 address.

   2.  Added facilities for announcing capabilities supported.

   3.  Added a tree affinity sub-TLV whereby ISs can request
       distribution tree association.



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   4.  Added multi-topology support.

   5.  Added control-plane support for TRILL Data frame fine-grained
       labels.  This support is independent of the data-plane
       representation.

   6.  Fixed the verified erratum [Err2869] in [RFC6326].

   Changes herein to TLVs and sub-TLVs specified in [RFC6326] are
   backward compatible.

1.1.  Conventions Used in This Document

   The terminology and acronyms defined in [RFC6325] are used herein
   with the same meaning.

   Additional acronyms and phrases used in this document are:

      BVL - Bit Vector Length

      BVO - Bit Vector Offset

      IIH - IS-IS Hello

      IS - Intermediate System.  For this document, all relevant
      intermediate systems are RBridges [RFC6325].

      MAC - Media Access Control

      MT - Multi-Topology

      NLPID - Network Layer Protocol Identifier

      SNPA - Subnetwork Point of Attachment (MAC Address)

   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 [RFC2119].

2.  TLV and Sub-TLV Extensions to IS-IS for TRILL

   This section, in conjunction with [RFC6165], specifies the data
   formats and code points for the TLVs and sub-TLVs for IS-IS to
   support the IETF TRILL protocol.  Information as to the number of
   occurrences allowed, such as for a TLV in a PDU or set of PDUs or for
   a sub-TLV in a TLV, is summarized in Section 5.





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2.1.  Group Address TLV

   The Group Address (GADDR) TLV, IS-IS TLV type 142, is carried in an
   LSP PDU and carries sub-TLVs that in turn advertise multicast group
   listeners.  The sub-TLVs that advertise listeners are specified
   below.  The sub-TLVs under GADDR constitute a new series of sub-TLV
   types (see Section 5.2).

   GADDR has the following format:

   +-+-+-+-+-+-+-+-+
   |Type=GADDR-TLV |                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
   |      sub-TLVs...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-...

   o  Type: TLV type, set to GADDR-TLV 142.

   o  Length: variable depending on the sub-TLVs carried.

   o  sub-TLVs: The Group Address TLV value consists of sub-TLVs
      formatted as described in [RFC5305].

2.1.1.  Group MAC Address Sub-TLV

   The Group MAC Address (GMAC-ADDR) sub-TLV is sub-TLV type number 1
   within the GADDR TLV.  In TRILL, it is used to advertise multicast
   listeners by MAC address as specified in Section 4.5.5 of [RFC6325].
   It has the following format:




















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   +-+-+-+-+-+-+-+-+
   |Type=GMAC-ADDR |                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  RESV |     Topology-ID       |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  RESV |     VLAN ID           |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Num Group Recs |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   GROUP RECORDS (1)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   GROUP RECORDS (2)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   .................                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   GROUP RECORDS (N)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where each group record is of the following form with k=6:

   +-+-+-+-+-+-+-+-+
   | Num of Sources|                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Group Address         (k bytes)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source 1 Address      (k bytes)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source 2 Address      (k bytes)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    .....                                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source M Address      (k bytes)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: GADDR sub-TLV type, set to 1 (GMAC-ADDR).

   o  Length: 5 + m + k*n = 5 + m + 6*n, where m is the number of group
      records and n is the sum of the number of group and source
      addresses.

   o  RESV: Reserved.  4-bit fields that MUST be sent as zero and
      ignored on receipt.

   o  Topology-ID: This field carries a topology ID [RFC5120] or zero if
      topologies are not in use.




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   o  VLAN ID: This carries the 12-bit VLAN identifier for all
      subsequent MAC addresses in this sub-TLV, or the value zero if no
      VLAN is specified.

   o  Num Group Recs: A 1-byte unsigned integer that is the number of
      group records in this sub-TLV.

   o  GROUP RECORDS: Each group record carries the number of sources.
      If this field is zero, it indicates a listener for (*,G), that is,
      a listener not restricted by source.  It then has a 6-byte
      (48-bit) multicast MAC address followed by 6-byte source MAC
      addresses.  If the sources do not fit in a single sub-TLV, the
      same group address may be repeated with different source addresses
      in another sub-TLV of another instance of the Group Address TLV.

   The GMAC-ADDR sub-TLV is carried only within a GADDR TLV.

2.1.2.  Group IPv4 Address Sub-TLV

   The Group IPv4 Address (GIP-ADDR) sub-TLV is IS-IS sub-TLV type 2
   within the GADDR TLV.  It has the same format as the Group MAC
   Address sub-TLV described in Section 2.1.1 except that k=4.  The
   fields are as follows:

   o  Type: sub-TLV type, set to 2 (GIP-ADDR).

   o  Length: 5 + m + k*n = 5 + m + 4*n, where m is the number of group
      records and n is the sum of the number of group and source
      addresses.

   o  Topology-ID: This field carries a topology ID [RFC5120] or zero if
      topologies are not in use.

   o  RESV: Must be sent as zero on transmission and is ignored on
      receipt.

   o  VLAN ID: This carries a 12-bit VLAN identifier that is valid for
      all subsequent addresses in this sub-TLV, or the value zero if no
      VLAN is specified.

   o  Num Group Recs: A 1-byte unsigned integer that is the number of
      group records in this sub-TLV.









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   o  GROUP RECORDS: Each group record carries the number of sources.
      If this field is zero, it indicates a listener for (*,G), that is,
      a listener not restricted by source.  It then has a 4-byte
      (32-bit) IPv4 Group Address followed by 4-byte source IPv4
      addresses.  If the number of sources do not fit in a single sub-
      TLV, it is permitted to have the same group address repeated with
      different source addresses in another sub-TLV of another instance
      of the Group Address TLV.

   The GIP-ADDR sub-TLV is carried only within a GADDR TLV.

2.1.3.  Group IPv6 Address Sub-TLV

   The Group IPv6 Address (GIPV6-ADDR) sub-TLV is IS-IS sub-TLV type 3
   within the GADDR TLV.  It has the same format as the Group MAC
   Address sub-TLV described in Section 2.1.1 except that k=16.  The
   fields are as follows:

   o  Type: sub-TLV type, set to 3 (GIPV6-ADDR).

   o  Length: 5 + m + k*n = 5 + m + 16*n, where m is the number of group
      records and n is the sum of the number of group and source
      addresses.

   o  Topology-Id: This field carries a topology ID [RFC5120] or zero if
      topologies are not in use.

   o  RESV: Must be sent as zero on transmission and is ignored on
      receipt.

   o  VLAN ID: This carries a 12-bit VLAN identifier that is valid for
      all subsequent addresses in this sub-TLV, or the value zero if no
      VLAN is specified.

   o  Num Group Recs: A 1-byte unsigned integer that is the number of
      group records in this sub-TLV.

   o  GROUP RECORDS: Each group record carries the number of sources.
      If this field is zero, it indicates a listener for (*,G), that is,
      a listener not restricted by source.  It then has a 16-byte
      (128-bit) IPv6 Group Address followed by 16-byte source IPv6
      addresses.  If the number of sources do not fit in a single sub-
      TLV, it is permitted to have the same group address repeated with
      different source addresses in another sub-TLV of another instance
      of the Group Address TLV.

   The GIPV6-ADDR sub-TLV is carried only within a GADDR TLV.




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2.1.4.  Group Labeled MAC Address Sub-TLV

   The GMAC-ADDR sub-TLV of the Group Address (GADDR) TLV specified in
   Section 2.1.1 provides for a VLAN ID.  The Group Labeled MAC Address
   sub-TLV, below, extends this to a fine-grained label.

   +-+-+-+-+-+-+-+-+
   |Type=GLMAC-ADDR|                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  RESV |     Topology-ID       |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Fine-Grained Label                     | (3 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Num Group Recs |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   GROUP RECORDS (1)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   GROUP RECORDS (2)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   .................                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   GROUP RECORDS (N)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where each group record is of the following form with k=6:

   +-+-+-+-+-+-+-+-+
   | Num of Sources|                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Group Address         (k bytes)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source 1 Address      (k bytes)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source 2 Address      (k bytes)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    .....                                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Source M Address      (k bytes)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: GADDR sub-TLV type, set to 4 (GLMAC-ADDR).

   o  Length: 6 + m + k*n = 6 + m + 6*n, where m is the number of group
      records and n is the sum of the number of group and source
      addresses.




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   o  RESV: Reserved.  4-bit field that MUST be sent as zero and ignored
      on receipt.

   o  Topology-ID: This field carries a topology ID [RFC5120] or zero if
      topologies are not in use.

   o  Label: This carries the fine-grained label [RFC7172] identifier
      for all subsequent MAC addresses in this sub-TLV, or the value
      zero if no label is specified.

   o  Num Group Recs: A 1-byte unsigned integer that is the number of
      group records in this sub-TLV.

   o  GROUP RECORDS: Each group record carries the number of sources.
      If this field is zero, it indicates a listener for (*,G), that is,
      a listener not restricted by source.  It then has a 6-byte
      (48-bit) multicast address followed by 6-byte source MAC
      addresses.  If the sources do not fit in a single sub-TLV, the
      same group address may be repeated with different source addresses
      in another sub-TLV of another instance of the Group Address TLV.

   The GLMAC-ADDR sub-TLV is carried only within a GADDR TLV.

2.1.5.  Group Labeled IPv4 Address Sub-TLV

   The Group Labeled IPv4 Address (GLIP-ADDR) sub-TLV is IS-IS sub-TLV
   type 5 within the GADDR TLV.  It has the same format as the Group
   Labeled MAC Address sub-TLV described in Section 2.1.4 except that
   k=4.  The fields are as follows:

   o  Type: sub-TLV type, set to 5 (GLIP-ADDR).

   o  Length: 6 + m + k*n = 6 + m + 4*n, where m is the number of group
      records and n is the sum of the number of group and source
      addresses.

   o  Topology-ID: This field carries a topology ID [RFC5120] or zero if
      topologies are not in use.

   o  RESV: Must be sent as zero on transmission and is ignored on
      receipt.

   o  Label: This carries the fine-grained label [RFC7172] identifier
      for all subsequent IPv4 addresses in this sub-TLV, or the value
      zero if no label is specified.

   o  Num Group Recs: A 1-byte unsigned integer that is the number of
      group records in this sub-TLV.



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   o  GROUP RECORDS: Each group record carries the number of sources.
      If this field is zero, it indicates a listener for (*,G), that is,
      a listener not restricted by source.  It then has a 4-byte
      (32-bit) IPv4 Group Address followed by 4-byte source IPv4
      addresses.  If the number of sources do not fit in a single sub-
      TLV, it is permitted to have the same group address repeated with
      different source addresses in another sub-TLV of another instance
      of the Group Address TLV.

   The GLIP-ADDR sub-TLV is carried only within a GADDR TLV.

2.1.6.  Group Labeled IPv6 Address Sub-TLV

   The Group Labeled IPv6 Address (GLIPV6-ADDR) sub-TLV is IS-IS sub-TLV
   type 6 within the GADDR TLV.  It has the same format as the Group
   Labeled MAC Address sub-TLV described in Section 2.1.4 except that
   k=16.  The fields are as follows:

   o  Type: sub-TLV type, set to 6 (GLIPV6-ADDR).

   o  Length: 6 + m + k*n = 6 + m + 16*n, where m is the number of group
      records and n is the sum of the number of group and source
      addresses.

   o  Topology-Id: This field carries a topology ID [RFC5120] or zero if
      topologies are not in use.

   o  RESV: Must be sent as zero on transmission and is ignored on
      receipt.

   o  Label: This carries the fine-grained label [RFC7172] identifier
      for all subsequent IPv6 addresses in this sub-TLV, or the value
      zero if no label is specified.

   o  Num Group Recs: A 1-byte unsigned integer that is the number of
      group records in this sub-TLV.

   o  GROUP RECORDS: Each group record carries the number of sources.
      If this field is zero, it indicates a listener for (*,G), that is,
      a listener not restricted by source.  It then has a 16-byte
      (128-bit) IPv6 Group Address followed by 16-byte source IPv6
      addresses.  If the number of sources do not fit in a single sub-
      TLV, it is permitted to have the same group address repeated with
      different source addresses in another sub-TLV of another instance
      of the Group Address TLV.

   The GLIPV6-ADDR sub-TLV is carried only within a GADDR TLV.




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2.2.  Multi-Topology-Aware Port Capability Sub-TLVs

   TRILL makes use of the Multi-Topology-Aware Port Capability TLV (MT-
   Port-Cap-TLV) as specified in [RFC6165].  The following subsections
   specify the sub-TLVs transported by the MT-Port-Cap-TLV for TRILL.

2.2.1.  Special VLANs and Flags Sub-TLV

   In TRILL, a Special VLANs and Flags (VLAN-FLAGS) sub-TLV is carried
   in every IIH PDU.  It has the following format:

   +--+--+--+--+--+--+--+--+
   |    Type               |                         (1 byte)
   +--+--+--+--+--+--+--+--+
   |    Length             |                         (1 byte)
   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
   |    Port ID                                    | (2 bytes)
   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
   |    Sender Nickname                            | (2 bytes)
   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
   |AF|AC|VM|BY|     Outer.VLAN                    | (2 bytes)
   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
   |TR|R |R |R |     Designated-VLAN               | (2 bytes)
   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

   o  Type: sub-TLV type, set to MT-Port-Cap-TLV VLAN-FLAGS sub-TLV 1.

   o  Length: 8.

   o  Port ID: An ID for the port on which the enclosing TRILL IIH PDU
      is being sent as specified in [RFC6325], Section 4.4.2.

   o  Sender Nickname: If the sending IS is holding any nicknames as
      discussed in [RFC6325], Section 3.7, one MUST be included here.
      Otherwise, the field is set to zero.  This field is to support
      intelligent end stations that determine the egress IS (RBridge)
      for unicast data through a directory service or the like and that
      need a nickname for their first hop to insert as the ingress
      nickname to correctly format a TRILL Data frame (see [RFC6325],
      Section 4.6.2, point 8).  It is also referenced in connection with
      the VLANs Appointed Sub-TLV (see Section 2.2.5) and can be used as
      the egress on one-hop RBridge Channel messages [RFC7178], for
      example, those use for BFD over TRILL [RFC7175].

   o  Outer.VLAN: A copy of the 12-bit outer VLAN ID of the TRILL IIH
      frame containing this sub-TLV, as specified in [RFC6325], Section
      4.4.5.




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   o  Designated-VLAN: The 12-bit ID of the Designated VLAN for the
      link, as specified in [RFC6325], Section 4.2.4.2.

   o  AF, AC, VM, BY, and TR: These flag bits have the following
      meanings when set to one, as specified in the listed section of
      [RFC6325]:

           RFC 6325
      Bit  Section   Meaning if bit is one
      --------------------------------------

      AF   4.4.2     Originating IS believes it is Appointed
                     Forwarder for the VLAN and port on which the
                     containing IIH PDU was sent.

      AC   4.9.1     Originating port configured as an access port
                     (TRILL traffic disabled).

      VM   4.4.5     VLAN mapping detected on this link.

      BY   4.4.2     Bypass pseudonode.

      TR   4.9.1     Originating port configured as a trunk port
                     (end-station service disabled).

   o  R: Reserved bit.  MUST be sent as zero and ignored on receipt.

2.2.2.  Enabled-VLANs Sub-TLV

   The optional Enabled-VLANs sub-TLV specifies the VLANs enabled at the
   port of the originating IS on which the containing Hello was sent, as
   specified in [RFC6325], Section 4.4.2.  It has the following format:

   +-+-+-+-+-+-+-+-+
   |     Type      |                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | RESV  |  Start VLAN ID        |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | VLAN bit-map....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: sub-TLV type, set to MT-Port-Cap-TLV Enabled-VLANs sub-TLV
      2.

   o  Length: Variable, minimum 3.




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   o  RESV: 4 reserved bits that MUST be sent as zero and ignored on
      receipt.

   o  Start VLAN ID: The 12-bit VLAN ID that is represented by the high-
      order bit of the first byte of the VLAN bit-map.

   o  VLAN bit-map: The highest-order bit indicates the VLAN equal to
      the start VLAN ID, the next highest bit indicates the VLAN equal
      to start VLAN ID + 1, continuing to the end of the VLAN bit-map
      field.

   If this sub-TLV occurs more than once in a Hello, the set of enabled
   VLANs is the union of the sets of VLANs indicated by each of the
   Enabled-VLAN sub-TLVs in the Hello.

2.2.3.  Appointed Forwarders Sub-TLV

   The Designated RBridge (DRB) on a link uses the Appointed Forwarders
   sub-TLV to inform other ISs on the link that they are the designated
   VLAN-x forwarder for one or more ranges of VLAN IDs as specified in
   [RFC6439].  It has the following format:

   +-+-+-+-+-+-+-+-+
   |     Type      |                          (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                          (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Appointment Information (1)         |  (6 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Appointment Information (2)         |  (6 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   .................                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Appointment Information (N)         |  (6 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where each appointment is of the form:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Appointee Nickname              |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | RESV  |        Start.VLAN             |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | RESV  |        End.VLAN               |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






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   o  Type: sub-TLV type, set to MT-Port-Cap-TLV AppointedFwrdrs sub-TLV
      3.

   o  Length: 6*n bytes, where there are n appointments.

   o  Appointee Nickname: The nickname of the IS being appointed a
      forwarder.

   o  RESV: 4 bits that MUST be sent as zero and ignored on receipt.

   o  Start.VLAN, End.VLAN: This VLAN ID range is inclusive.  Setting
      both Start.VLAN and VLAN.end to the same value indicates a range
      of one VLAN ID.  If Start.VLAN is not equal to VLAN.end and
      Start.VLAN is 0x000, the sub-TLV is interpreted as if Start.VLAN
      was 0x001.  If Start.VLAN is not equal to VLAN.end and VLAN.end is
      0xFFF, the sub-TLV is interpreted as if VLAN.end was 0xFFE.  If
      VLAN.end is less than Start.VLAN, the sub-TLV is ignored.  If both
      Start.VLAN and VLAN.end are 0x000 or both are 0xFFF, the sub-TLV
      is ignored.  The values 0x000 or 0xFFF are not valid VLAN IDs, and
      a port cannot be enabled for them.

   An IS's nickname may occur as Appointed Forwarder for multiple VLAN
   ranges by occurrences of this sub-TLV within the same or different MT
   Port Capability TLVs within an IIH PDU.  See [RFC6439].

2.2.4.  Port TRILL Version Sub-TLV

   The Port TRILL Version (PORT-TRILL-VER) sub-TLV indicates the maximum
   version of the TRILL standard supported and the support of optional
   hop-by-hop capabilities.  By implication, lower versions are also
   supported.  If this sub-TLV is missing from an IIH, it is assumed
   that the originating IS only supports the base version (version zero)
   of the protocol [RFC6325] and supports no optional capabilities
   indicated by this sub-TLV.

   +-+-+-+-+-+-+-+-+
   | Type          |              (1 byte)
   +-+-+-+-+-+-+-+-+
   | Length        |              (1 byte)
   +-+-+-+-+-+-+-+-+
   | Max-version   |              (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   | Capabilities and Header Flags Supported |  (4 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+
    0                   1                 3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7   0 1





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   o  Type: MT-Port-Cap-TLV sub-TLV type, set to 7 (PORT-TRILL-VER).

   o  Length: 5.

   o  Max-version: A one-byte unsigned integer set to the maximum
      version supported.

   o  Capabilities and Header Flags Supported: A bit vector of 32 bits
      numbered 0 through 31 in network order.  Bits 3 through 13
      indicate that the corresponding TRILL Header hop-by-hop extended
      flags [RFC7179] are supported.  Bits 0 through 2 and 14 to 31 are
      reserved to indicate support of optional capabilities.  A one bit
      indicates that the flag or capability is supported by the sending
      IS.  Bits in this field MUST be set to zero except as permitted
      for a capability being advertised or if a hop-by-hop extended
      header flag is supported.

   This sub-TLV, if present, MUST occur in an MT-Port-Cap-TLV in a TRILL
   IIH.  If there is more than one occurrence, the minimum of the
   supported versions is assumed to be correct and a capability or
   header flag is assumed to be supported only if indicated by all
   occurrences.  The flags and capabilities for which support can be
   indicated in this sub-TLV are disjoint from those in the TRILL-VER
   sub-TLV (Section 2.3.1) so they cannot conflict.  The flags and
   capabilities indicated in this sub-TLV relate to hop-by-hop
   processing that can differ between the ports of an IS (RBridge) and
   thus must be advertised in IIHs.  For example, a capability requiring
   cryptographic hardware assist might be supported on some ports and
   not others.  However, the TRILL version is the same as that in the
   PORT-TRILL-VER sub-TLV.  An IS, if it is adjacent to the sending IS
   of TRILL version sub-TLV(s), uses the TRILL version it received in
   PORT-TRILL-VER sub-TLV(s) in preference to that received in TRILL-VER
   sub-TLV(s).


















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2.2.5.  VLANs Appointed Sub-TLV

   The optional VLANs Appointed sub-TLV specifies, for the port of the
   originating IS on which the containing Hello was sent, the VLANs for
   which it is Appointed Forwarder.  This sub-TLV has the following
   format:

   +-+-+-+-+-+-+-+-+
   |     Type      |                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | RESV  |  Start VLAN ID        |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | VLAN bit-map....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: sub-TLV type, set to MT-Port-Cap-TLV VLANS-Appointed sub-TLV
      8.

   o  Length: Variable, minimum 3.

   o  RESV: 4 reserved bits that MUST be sent as zero and ignored on
      receipt.

   o  Start VLAN ID: The 12-bit VLAN ID that is represented by the high-
      order bit of the first byte of the VLAN bit-map.

   o  VLAN bit-map: The highest-order bit indicates the VLAN equal to
      the start VLAN ID, the next highest bit indicates the VLAN equal
      to start VLAN ID + 1, continuing to the end of the VLAN bit-map
      field.

   If this sub-TLV occurs more than once in a Hello, the originating IS
   is declaring that it believes itself to be Appointed Forwarder on the
   port on which the enclosing IIH was sent for the union of the sets of
   VLANs indicated by each of the VLANs-Appointed sub-TLVs in the Hello.

2.3.  Sub-TLVs of the Router Capability and MT-Capability TLVs

   The Router Capability TLV is specified in [RFC4971] and the MT-
   Capability TLV in [RFC6329].  All of the following sub-sections
   specify sub-TLVs that can be carried in the Router Capability TLV
   (#242) and the MT-Capability TLV (#144) with the same sub-TLV number
   for both TLVs.  These TLVs are in turn carried only by LSPs.






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2.3.1.  TRILL Version Sub-TLV

   The TRILL Version (TRILL-VER) sub-TLV indicates the maximum version
   of the TRILL standard supported and the support of optional
   capabilities by the originating IS.  By implication, lower versions
   are also supported.  If this sub-TLV is missing, it is assumed that
   the originating IS only supports the base version (version zero) of
   the protocol [RFC6325], and no optional capabilities indicated by
   this sub-TLV are supported.

   +-+-+-+-+-+-+-+-+
   | Type          |              (1 byte)
   +-+-+-+-+-+-+-+-+
   | Length        |              (1 byte)
   +-+-+-+-+-+-+-+-+
   | Max-version   |              (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   | Capabilities and Header Flags Supported |  (4 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+-+
    0                   1                 3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7   0 1

   o  Type: Router Capability sub-TLV type, set to 13 (TRILL-VER).

   o  Length: 5.

   o  Max-version: A one-byte unsigned integer set to the maximum
      version supported.

   o  Capabilities and Header Flags Supported: A bit vector of 32 bits
      numbered 0 through 31 in network order.  Bits 14 through 31
      indicate that the corresponding TRILL Header extended flags
      [RFC7179] are supported.  Bits 0 through 13 are reserved to
      indicate support of optional capabilities.  A one bit indicates
      that the originating IS supports the flag or capability.  For
      example, support of multi-level TRILL IS-IS [MultiLevel].  Bits in
      this field MUST be set to zero except as permitted for a
      capability being advertised or an extended header flag supported.

   This sub-TLV, if present in a Router Capability TLV, MUST occur in
   the LSP number zero for the originating IS.  If found in a Router
   Capability TLV in other fragments, it is ignored.  If there is more
   than one occurrence in LSP number zero, the minimum of the supported
   versions is assumed to be correct, and an extended header flag or
   capability is assumed to be supported only if indicated by all
   occurrences.  The flags and capabilities for which support can be
   indicated in this sub-TLV are disjoint from those in the PORT-TRILL-
   VER sub-TLV (Section 2.2.4) so they cannot conflict.  However, the



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   TRILL version is the same as that in the PORT-TRILL-VER sub-TLV, and
   an IS that is adjacent to the originating IS of TRILL-VER sub-TLV(s)
   uses the TRILL version it received in PORT-TRILL-VER sub-TLV(s) in
   preference to that received in TRILL-VER sub-TLV(s).

   For multi-topology-aware TRILL Switches, the TRILL version and
   capabilities announced for the base topology are assumed to apply to
   all topologies for which a separate TRILL version announcement does
   not occur in an MT-Capability TLV.  Such announcements for non-zero
   topologies need not occur in fragment zero.

2.3.2.  Nickname Sub-TLV

   The Nickname (NICKNAME) Router Capability sub-TLV carries information
   about the nicknames of the originating IS, along with information
   about its priority to hold those nicknames and the priority for each
   nickname to be a tree root as specified in [RFC6325], Section 3.7.3.
   Multiple instances of this sub-TLV may occur.

   +-+-+-+-+-+-+-+-+
   |Type = NICKNAME|                         (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                         (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                NICKNAME RECORDS (1)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                NICKNAME RECORDS (2)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   .................                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                NICKNAME RECORDS (N)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where each nickname record is of the form:

   +-+-+-+-+-+-+-+-+
   | Nickname.Pri  |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Tree Root Priority        |  (2 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Nickname            |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: Router Capability and MT-Capability sub-TLV type, set to 6
      (NICKNAME).

   o  Length: 5*n, where n is the number of nickname records present.




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   o  Nickname.Pri: An 8-bit unsigned integer priority to hold a
      nickname as specified in Section 3.7.3 of [RFC6325].

   o  Tree Root Priority: This is an unsigned 16-bit integer priority to
      be a tree root as specified in Section 4.5 of [RFC6325].

   o  Nickname: This is an unsigned 16-bit integer as specified in
      Section 3.7 of [RFC6325].

2.3.3.  Trees Sub-TLV

   Each IS providing TRILL service uses the TREES sub-TLV to announce
   three numbers related to the computation of distribution trees as
   specified in Section 4.5 of [RFC6325].  Its format is as follows:

   +-+-+-+-+-+-+-+-+
   |Type =  TREES  |                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |  Length       |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Number of trees to compute    |  (2 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Maximum trees able to compute |  (2 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Number of trees to use        |  (2 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: Router Capability and MT-Capability sub-TLV type, set to 7
      (TREES).

   o  Length: 6.

   o  Number of trees to compute: An unsigned 16-bit integer as
      specified in Section 4.5 of [RFC6325].

   o  Maximum trees able to compute: An unsigned 16-bit integer as
      specified in Section 4.5 of [RFC6325].

   o  Number of trees to use: An unsigned 16-bit integer as specified in
      Section 4.5 of [RFC6325].

2.3.4.  Tree Identifiers Sub-TLV

   The Tree Identifiers (TREE-RT-IDs) sub-TLV is an ordered list of
   nicknames.  When originated by the IS that has the highest priority
   to be a tree root, it lists the distribution trees that the other ISs
   are required to compute as specified in Section 4.5 of [RFC6325].  If




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   this information is spread across multiple sub-TLVs, the starting
   tree number is used to allow the ordered lists to be correctly
   concatenated.  The sub-TLV format is as follows:

   +-+-+-+-+-+-+-+-+
   |Type=TREE-RT-IDs|               (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Starting Tree Number         |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Nickname (K-th root)      |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Nickname (K+1 - th root)  |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Nickname (...)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: Router Capability and MT-Capability sub-TLV type, set to 8
      (TREE-RT-IDs).

   o  Length: 2 + 2*n, where n is the number of nicknames listed.

   o  Starting Tree Number: This identifies the starting tree number of
      the nicknames that are trees for the domain.  This is set to 1 for
      the sub-TLV containing the first list.  Other Tree-Identifiers
      sub-TLVs will have the number of the starting list they contain.
      In the event the same tree identifier can be computed from two
      such sub-TLVs and they are different, then it is assumed that this
      is a transient condition that will get cleared.  During this
      transient time, such a tree SHOULD NOT be computed unless such
      computation is indicated by all relevant sub-TLVs present.

   o  Nickname: The nickname at which a distribution tree is rooted.

2.3.5.  Trees Used Identifiers Sub-TLV

   This Router Capability sub-TLV has the same structure as the Tree
   Identifiers sub-TLV specified in Section 2.3.4.  The only difference
   is that its sub-TLV type is set to 9 (TREE-USE-IDs), and the trees
   listed are those that the originating IS wishes to use as specified
   in [RFC6325], Section 4.5.









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2.3.6.  Interested VLANs and Spanning Tree Roots Sub-TLV

   The value of this sub-TLV consists of a VLAN range and information in
   common to all of the VLANs in the range for the originating IS.  This
   information consists of flags, a variable length list of spanning
   tree root bridge IDs, and an Appointed Forwarder status lost counter,
   all as specified in the sections of [RFC6325] listed with the
   respective information items below.

   In the set of LSPs originated by an IS, the union of the VLAN ranges
   in all occurrences of this sub-TLV MUST be the set of VLANs for which
   the originating IS is Appointed Forwarder on at least one port, and
   the VLAN ranges in multiple VLANs sub-TLVs for an IS MUST NOT overlap
   unless the information provided about a VLAN is the same in every
   instance.  However, as a transient state, these conditions may be
   violated.  If a VLAN is not listed in any INT-VLAN sub-TLV for an IS,
   that IS is assumed to be uninterested in receiving traffic for that
   VLAN.  If a VLAN appears in more than one INT-VLAN sub-TLV for an IS
   with different information in the different instances, the following
   apply:

   -  If those sub-TLVs provide different nicknames, it is unspecified
      which nickname takes precedence.
   -  The largest Appointed Forwarder status lost counter, using serial
      number arithmetic [RFC1982], is used.
   -  The originating IS is assumed to be attached to a multicast IPv4
      router for that VLAN if any of the INT-VLAN sub-TLVs assert that
      it is so connected and similarly for IPv6 multicast router
      attachment.
   -  The root bridge lists from all of the instances of the VLAN for
      the originating IS are merged.

   To minimize such occurrences, wherever possible, an implementation
   SHOULD advertise the update to an interested VLAN and Spanning Tree
   Roots sub-TLV in the same LSP fragment as the advertisement that it
   replaces.  Where this is not possible, the two affected LSP fragments
   should be flooded as an atomic action.  An IS that receives an update
   to an existing interested VLAN and Spanning Tree Roots sub-TLV can
   minimize the potential disruption associated with the update by
   employing a hold-down timer prior to processing the update so as to
   allow for the receipt of multiple LSP fragments associated with the
   same update prior to beginning processing.









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   The sub-TLV layout is as follows:

   +-+-+-+-+-+-+-+-+
   |Type = INT-VLAN|                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Nickname                    |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+
   |   Interested VLANS                            |        (4 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+
   |   Appointed Forwarder Status Lost Counter     |        (4 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+
   |         Root Bridges                                |  (6*n bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+

   o  Type: Router Capability and MT-Capability sub-TLV type, set to 10
      (INT-VLAN).

   o  Length: 10 + 6*n, where n is the number of root bridge IDs.

   o  Nickname: As specified in [RFC6325], Section 4.2.4.4, this field
      may be used to associate a nickname held by the originating IS
      with the VLAN range indicated.  When not used in this way, it is
      set to zero.

   o  Interested VLANS: The Interested VLANs field is formatted as shown
      below.

        0    1    2    3     4 - 15      16 - 19     20 - 31
      +----+----+----+----+------------+----------+------------+
      | M4 | M6 |  R |  R | VLAN.start |   RESV   |  VLAN.end  |
      +----+----+----+----+------------+----------+------------+

      -  M4, M6: These bits indicate, respectively, that there is an
         IPv4 or IPv6 multicast router on a link for which the
         originating IS is Appointed Forwarder for every VLAN in the
         indicated range as specified in [RFC6325], Section 4.2.4.4,
         item 5.1.

      -  R, RESV: These reserved bits MUST be sent as zero and are
         ignored on receipt.

      -  VLAN.start and VLAN.end: This VLAN ID range is inclusive.
         Setting both VLAN.start and VLAN.end to the same value
         indicates a range of one VLAN ID.  If VLAN.start is not equal
         to VLAN.end and VLAN.start is 0x000, the sub-TLV is interpreted
         as if VLAN.start was 0x001.  If VLAN.start is not equal to



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         VLAN.end and VLAN.end is 0xFFF, the sub-TLV is interpreted as
         if VLAN.end was 0xFFE.  If VLAN.end is less than VLAN.start,
         the sub-TLV is ignored.  If both VLAN.start and VLAN.end are
         0x000 or both are 0xFFF, the sub-TLV is ignored.  The values
         0x000 or 0xFFF are not valid VLAN IDs, and a port cannot be
         enabled for them.

   o  Appointed Forwarder Status Lost Counter: This is a count of how
      many times a port that was Appointed Forwarder for the VLANs in
      the range given has lost the status of being an Appointed
      Forwarder for some port as discussed in Section 4.8.3 of
      [RFC6325].  It is initialized to zero at an IS when the zeroth LSP
      sequence number is initialized.  No special action need be taken
      at rollover; the counter just wraps around.

   o  Root Bridges: The list of zero or more spanning tree root bridge
      IDs is the set of root bridge IDs seen for all ports for which the
      IS is Appointed Forwarder for the VLANs in the specified range as
      discussed in [RFC6325], Section 4.9.3.2.  While, of course, at
      most one spanning tree root could be seen on any particular port,
      there may be multiple ports in the same VLANs connected to
      different bridged LANs with different spanning tree roots.

   An INT-VLAN sub-TLV asserts that the information provided (multicast
   router attachment, Appointed Forwarder status lost counter, and root
   bridges) is the same for all VLANs in the range specified.  If this
   is not the case, the range MUST be split into subranges meeting this
   criteria.  It is always safe to use sub-TLVs with a "range" of one
   VLAN ID, but this may be too verbose.

2.3.7.  VLAN Group Sub-TLV

   The VLAN Group sub-TLV consists of two or more VLAN IDs as specified
   in [RFC6325], Section 4.8.4.  This sub-TLV indicates that shared VLAN
   learning is occurring at the originating IS between the listed VLANs.
   It is structured as follows:

   +-+-+-+-+-+-+-+-+
   |Type=VLAN-GROUP|                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | RESV  |  Primary VLAN ID      |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | RESV  |  Secondary VLAN ID    |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  more Secondary VLAN IDs ...     (2 bytes each)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   o  Type: Router Capability and MT-Capability sub-TLV type, set to 14
      (VLAN-GROUP).

   o  Length: 4 + 2*n, where n is the number of secondary VLAN ID fields
      beyond the first.  n MAY be zero.

   o  RESV: a 4-bit field that MUST be sent as zero and ignored on
      receipt.

   o  Primary VLAN ID: This identifies the primary VLAN ID.

   o  Secondary VLAN ID: This identifies a secondary VLAN in the VLAN
      Group.

   o  more Secondary VLAN IDs: zero or more byte pairs, each with the
      top 4 bits as a RESV field and the low 12 bits as a VLAN ID.

2.3.8.  Interested Labels and Spanning Tree Roots Sub-TLV

   An IS that can handle fine-grained labeling [RFC7172] announces its
   fine-grained label connectivity and related information in the
   Interested Labels and Spanning Tree Roots sub-TLV (INT-LABEL).  It is
   a variation of the Interested VLANs and Spanning Tree Roots sub-TLV
   (INT-VLAN) and is structured as follows.

   +-+-+-+-+-+-+-+-+
   |Type=INT-LABEL |                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Nickname                    |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+
   |   Interested Labels                                 |  (7 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+
   |   Appointed Forwarder Status Lost Counter           |  (4 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+
   |         Root Bridges                                |  (6*n bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+

   o  Type: Router Capability and MT-Capability sub-TLV type, set to 15
      (INT-LABEL).

   o  Length: 11 + 6*n, where n is the number of root bridge IDs.

   o  Nickname: This field may be used to associate a nickname held by
      the originating IS with the Interested Labels indicated.  When not
      used in this way, it is set to zero.




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   o  Interested Labels: The Interested Labels field is seven bytes long
      and formatted as shown below.

        0  1  2  3  4  5  6  7
      +--+--+--+--+--+--+--+--+
      |M4|M6|BM| R| R| R| R| R|               .               .
      +--+--+--+--+--+--+--+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Label.start - 24 bits                  |
      +--+--+--+--+--+--+--+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Label.end or bit-map - 24 bits              |
      +--+--+--+--+--+--+--+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        0                          1                   2
        0  1  2  3  4  5  6  7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3

      -  M4, M6: These bits indicate, respectively, that there is an
         IPv4 or IPv6 multicast router on a link to which the
         originating IS is Appointed Forwarder for the VLAN
         corresponding to every label in the indicated range.

      -  BM: If the BM (bit-map) bit is zero, the last three bytes of
         the Interested Labels is a Label.end label number.  If the BM
         bit is one, those bytes are a bit-map as described below.

      -  R: These reserved bits MUST be sent as zero and are ignored on
         receipt.

      -  Label.start and Label.end: If the BM bit is zero, this fine-
         grained label [RFC7172] ID range is inclusive.  These fields
         are treated as unsigned integers.  Setting them both to the
         same label ID value indicates a range of one label ID.  If
         Label.end is less than Label.start, the sub-TLV is ignored.

      -  Label.start and bit-map: If the BM bit is one, the fine-grained
         labels that the IS is interested in are indicated by a 24-bit
         bit-map.  The interested labels are the Label.start number plus
         the bit number of each one bit in the bit-map.  So, if bit zero
         of the bit-map is a one, the IS is interested in the label with
         value Label.start, and if bit 23 of the bit-map is a one, the
         IS is interested in the label with value Label.start+23.

   o  Appointed Forwarder Status Lost Counter: This is a count of how
      many times a port that was Appointed Forwarder for a VLAN mapping
      to the fine-grained label in the range or bit-map given has lost
      the status of being an Appointed Forwarder as discussed in Section
      4.8.3 of [RFC6325].  It is initialized to zero at an IS when the
      zeroth LSP sequence number is initialized.  No special action need
      be taken at rollover; the counter just wraps around.




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   o  Root Bridges: The list of zero or more spanning tree root bridge
      IDs is the set of root bridge IDs seen for all ports for which the
      IS is Appointed Forwarder for a VLAN mapping to the fine-grained
      label in the specified range or bit-map.  (See [RFC6325], Section
      4.9.3.2.)  While, of course, at most one spanning tree root could
      be seen on any particular port, there may be multiple relevant
      ports connected to different bridged LANs with different spanning
      tree roots.

   An INT-LABEL sub-TLV asserts that the information provided (multicast
   router attachment, Appointed Forwarder status lost counter, and root
   bridges) is the same for all labels specified.  If this is not the
   case, the sub-TLV MUST be split into subranges and/or separate bit
   maps meeting this criteria.  It is always safe to use sub-TLVs with a
   "range" of one VLAN ID, but this may be too verbose.

2.3.9.  RBridge Channel Protocols Sub-TLV

   An IS announces the RBridge Channel protocols [RFC7178] it supports
   through use of this sub-TLV.

   +-+-+-+-+-+-+-+-+
   |Type=RBCHANNELS|                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
   |   Zero or more bit vectors                            (variable)
   +-+-+-+-...

   o  Type: Router Capability and MT-Capability RBridge Channel
      Protocols sub-TLV, set to 16 (RBCHANNELS).

   o  Length: variable.

   o  Bit Vectors: Zero or more byte-aligned bit vectors where a one bit
      indicates support of a particular RBridge Channel protocol.  Each
      byte-aligned bit vector is formatted as follows:

      | 0  1  2  3  4  5  6  7| 8  9 10 11 12 13 14 15|
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      |  Bit Vector Length |     Bit Vector Offset    |
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      |  bits
      +--+--+--...

      The Bit Vector Length (BVL) is a seven-bit unsigned integer field
      giving the number of bytes of bit vector.  The Bit Vector Offset
      (BVO) is a nine-bit unsigned integer field.



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      The bits in each bit vector are numbered in network order, the
      high-order bit of the first byte of bits being bit 0 + 8*BVO, the
      low-order bit of that byte being 7 + 8*BVO, the high order bit of
      the second byte being 8 + 8*BVO, and so on for BVL bytes.  A bit
      vector of RBridge Channel protocols supported MUST NOT extend
      beyond the end of the value in the sub-TLV in which it occurs.  If
      it does, it is ignored.  If multiple byte-aligned bit vectors are
      present in one such sub-TLV, their representations are contiguous,
      the BVL field for the next starting immediately after the last
      byte of bits for the previous bit vector.  The one or more bit
      vectors present MUST exactly fill the sub-TLV value.  If there are
      one or two bytes of value left over, they are ignored; if more
      than two, an attempt is made to parse them as one or more bit
      vectors.

      If different bit vectors overlap in the protocol number space they
      refer to and they have inconsistent bit values for a channel
      protocol, support for the protocol is assumed if any of these bit
      vectors has a 1 for that protocol.

      The absence of any occurrences of this sub-TLV in the LSP for an
      IS implies that the IS does not support the RBridge Channel
      facility.  To avoid wasted space, trailing bit vector zero bytes
      SHOULD be eliminated by reducing BVL, any null bit vectors (ones
      with BVL equal to zero) eliminated, and generally the most compact
      encoding used.  For example, support for channel protocols 1 and
      32 could be encoded as

         BVL = 5
         BVO = 0
          0b01000000
          0b00000000
          0b00000000
          0b00000000
          0b10000000

      or as

         BVL = 1
         BVO = 0
          0b01000000
         BLV = 1
         BVO = 4
          0b1000000

      The first takes 7 bytes while the second takes only 6; thus, the
      second would be preferred.




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   In multi-topology-aware RBridges, RBridge Channel protocols for which
   support is announced in the base topology are assumed to be supported
   in all topologies for which there is no separate announcement for
   RBridge Channel protocol support.

2.3.10.  Affinity Sub-TLV

   Association of an IS to a multi-destination distribution tree through
   a specific path is accomplished by using the Affinity sub-TLV.  The
   announcement of an Affinity sub-TLV by RB1 with the nickname of RB2
   as the first part of an Affinity Record in the sub-TLV value is a
   request by RB1 that all ISs in the campus connect RB2 as a child of
   RB1 when calculating any of the trees listed in that Affinity Record.
   Examples of use include [Affinity] and [Resilient].

   The structure of the Affinity sub-TLV is shown below.

   +-+-+-+-+-+-+-+-+
   | Type=AFFINITY |                (1 byte)
   +-+-+-+-+-+-+-+-+
   | Length        |                (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   AFFINITY RECORD 1                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   AFFINITY RECORD 2                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   ..........
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   AFFINITY RECORD N                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where each AFFINITY RECORD is structured as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Nickname                    |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Affinity Flags |                (1 byte)
   +-+-+-+-+-+-+-+-+
   |Number of trees|                (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Tree-num of 1st root        |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Tree-num of 2nd root        |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          ..........         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Tree-num of Nth root        |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   o  Type: Router Capability and MT-Capability sub-TLV type, set to 17
      (AFFINITY).

   o  Length: size of all Affinity Records included, where an Affinity
      Record listing n tree roots is 4+2*n bytes long.

   o  Nickname: 16-bit nickname of the IS whose associations to the
      multi-destination trees listed in the Affinity Record are through
      the originating IS.

   o  Affinity Flags: 8 bits reserved for future needs to provide
      additional information about the affinity being announced.  MUST
      be sent as zero and ignored on receipt.

   o  Number of trees: A one-byte unsigned integer giving the number of
      trees for which affinity is being announced by this Affinity
      Record.

   o  Tree-num of roots: The tree numbers of the distribution trees this
      Affinity Record is announcing.

   There is no need for a field giving the number of Affinity Records as
   this can be determined by processing those records.

2.3.11 Label Group Sub-TLV

   The Label Group sub-TLV consists of two or more fine-grained label
   [RFC7172] IDs.  This sub-TLV indicates that shared label MAC address
   learning is occurring at the announcing IS between the listed labels.
   It is structured as follows:

   +-+-+-+-+-+-+-+-+
   |Typ=LABEL-GROUP|                                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Primary Label ID                             |  (3 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Secondary Label ID                           |  (3 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  more Secondary Label IDs ...                   (3 bytes each)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: Router Capability and MT-Capability sub-TLV type, set to 18
      (LABEL-GROUP).

   o  Length: 6 + 3*n, where n is the number of secondary VLAN ID fields
      beyond the first.  n MAY be zero.



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   o  Primary Label ID: This identifies the primary Label ID.

   o  Secondary Label ID: This identifies a secondary Label ID in the
      Label Group.

   o  more Secondary Label IDs: zero or more byte triples, each with a
      Label ID.

2.4.  MTU Sub-TLV for Extended Reachability and MT-ISN TLVs

   The MTU sub-TLV is used to optionally announce the MTU of a link as
   specified in [RFC6325], Section 4.2.4.4.  It occurs within the
   Extended Reachability (#22) and MT-ISN (Intermediate System
   Neighbors) (#222) TLVs.

   +-+-+-+-+-+-+-+-+
   | Type = MTU    |                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |F|  RESV       |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               MTU             |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: Extended Reachability and MT-ISN sub-TLV type, set to MTU
      sub-TLV 28.

   o  Length: 3.

   o  F: Failed.  This bit is a one if MTU testing failed on this link
      at the required campus-wide MTU.

   o  RESV: 7 bits that MUST be sent as zero and ignored on receipt.

   o  MTU: This field is set to the largest successfully tested MTU size
      for this link or zero if it has not been tested, as specified in
      Section 4.3.2 of [RFC6325].

2.5.  TRILL Neighbor TLV

   The TRILL Neighbor TLV is used in TRILL broadcast link IIH PDUs (see
   Section 4.1 below) in place of the IS Neighbor TLV, as specified in
   Section 4.4.2.1 of [RFC6325] and in [RFC7177].  The structure of the
   TRILL Neighbor TLV is as follows:






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   +-+-+-+-+-+-+-+-+
   |     Type      |                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |   Length      |                  (1 byte)
   +-+-+-+-+-+-+-+-+
   |S|L|R|  SIZE   |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Neighbor RECORDS (1)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Neighbor RECORDS (2)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   .................                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Neighbor RECORDS (N)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The information present for each neighbor is as follows:

   +-+-+-+-+-+-+-+-+
   |F|O|  RESV     |                (1 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      MTU                    |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+
   |      SNPA (MAC Address)                           | (SIZE bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+-+-+-+

   o  Type: TLV type, set to TRILL Neighbor TLV 145.

   o  Length: 1 + (SIZE+3)*n, where n is the number of neighbor records,
      which may be zero.

   o  S: Smallest flag.  If this bit is a one, then the list of
      neighbors includes the neighbor with the smallest MAC address
      considered as an unsigned integer.

   o  L: Largest flag.  If this bit is a one, then the list of neighbors
      includes the neighbor with the largest MAC address considered as
      an unsigned integer.

   o  R, RESV: These bits are reserved and MUST be sent as zero and
      ignored on receipt.

   o  SIZE: The SNPA size as an unsigned integer in bytes except that 6
      is encoded as zero.  An actual size of zero is meaningless and
      cannot be encoded.  The meaning of the value 6 in this field is
      reserved, and TRILL Neighbor TLVs received with a SIZE of 6 are
      ignored.  The SIZE is inherent to the technology of a link and is
      fixed for all TRILL Neighbor TLVs on that link but may vary



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      between different links in the campus if those links are different
      technologies, for example, 6 for EUI-48 SNPAs or 8 for EUI-64
      SNPAs [RFC7042].  (The SNPA size on the various links in a TRILL
      campus is independent of the System ID size.)

   o  F: Failed.  This bit is a one if MTU testing to this neighbor
      failed at the required campus-wide MTU (see [RFC6325], Section
      4.3.1).

   o  O: OOMF.  This bit is a one if the IS sending the enclosing TRILL
      Neighbor TLV is willing to offer the Overload Originated Multi-
      destination Frame (OOMF) service [RFC7180] to the IS whose port
      has the SNPA in the enclosing Neighbor RECORD.

   o  MTU: This field is set to the largest successfully tested MTU size
      for this neighbor or to zero if it has not been tested.

   o  SNPA (MAC Address): Subnetwork Point of Attachment of the
      neighbor.

   As specified in [RFC7177] and Section 4.4.2.1 of [RFC6325], all MAC
   addresses may fit into one TLV, in which case both the S and L flags
   would be set to one in that TLV.  If the MAC addresses don't fit into
   one TLV, the highest MAC address in a TRILL Neighbor TLV with the L
   flag zero MUST also appear as a MAC address in some other TRILL
   Neighbor TLV (possibly in a different TRILL IIH PDU).  Also, the
   lowest MAC address in a TRILL Neighbor TLV with the S flag zero MUST
   also appear in some other TRILL Neighbor TLV (possibly in a different
   TRILL IIH PDU).  If an IS believes it has no neighbors, it MUST send
   a TRILL Neighbor TLV with an empty list of neighbor RECORDS, which
   will have both the S and L bits on.

3.  MTU PDUs

   The IS-IS MTU-probe and MTU-ack PDUs are used to optionally determine
   the MTU on a link between ISs as specified in Section 4.3.2 of
   [RFC6325] and in [RFC7177].

   The MTU PDUs have the IS-IS PDU common header (up through the Maximum
   Area Addresses byte) with PDU Type numbers as indicated in Section 5.
   They also have a common fixed MTU PDU header as shown below that is 8
   + 2*(ID Length) bytes long, 20 bytes in the case of the usual 6-bytes
   System IDs.








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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    PDU Length                 |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....+-+-+
   |    Probe ID                      (6 bytes)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....+-+-+
   |    Probe Source ID               (ID Length bytes)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....+-+-+
   |    Ack Source ID                 (ID Length bytes)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....+-+-+

   As with other IS-IS PDUs, the PDU Length gives the length of the
   entire IS-IS packet starting with and including the IS-IS common
   header.

   The Probe ID field is an opaque 48-bit quantity set by the IS issuing
   an MTU-probe and copied by the responding IS into the corresponding
   MTU-ack.  For example, an IS creating an MTU-probe could compose this
   quantity from a port identifier and probe sequence number relative to
   that port.

   The Probe Source ID is set by an IS issuing an MTU-probe to its
   System ID and copied by the responding IS into the corresponding MTU-
   ack.  The Ack Source ID is set to zero in MTU-probe PDUs and ignored
   on receipt.  An IS issuing an MTU-ack sets the Ack Source ID field to
   its System ID.  The System ID length is usually 6 bytes but could be
   a different value as indicated by the ID Length field in the IS-IS
   PDU Header.

   The TLV area follows the MTU PDU header area.  This area MAY contain
   an Authentication TLV and MUST be padded with the Padding TLV to the
   exact size being tested.  Since the minimum size of the Padding TLV
   is 2 bytes, it would be impossible to pad to exact size if the total
   length of the required information-bearing fixed fields and TLVs
   added up to 1 byte less than the desired length.  However, the length
   of the fixed fields and substantive TLVs for MTU PDUs is expected to
   be quite small compared with their minimum length (minimum 1470-byte
   MTU on an IEEE 802.3 link, for example), so this should not be a
   problem.













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4.  Use of Existing PDUs and TLVs

   The sub-sections below provide details of TRILL use of existing PDUs
   and TLVs.

4.1.  TRILL IIH PDUs

   The TRILL IIH PDU is the variation of the IIH PDU used by the TRILL
   protocol.  Section 4.4 of the TRILL standard [RFC6325] and [RFC7177]
   specify the contents of the TRILL IIH and how its use in TRILL
   differs from Layer 3 LAN IIH PDU use.  The adjacency state machinery
   for TRILL neighbors is specified in detail in [RFC7177].

   In a TRILL IIH PDU, the IS-IS common header and the fixed PDU Header
   are the same as a Level 1 IIH PDU.

   The IS-IS Neighbor TLV (6) is not used in a TRILL IIH and is ignored
   if it appears there.  Instead, TRILL LAN IIH PDUs use the TRILL
   Neighbor TLV (see Section 2.5).

4.2.  Area Address

   TRILL uses a fixed zero Area Address as specified in [RFC6325],
   Section 4.2.3.  This is encoded in a 4-byte Area Address TLV (TLV #1)
   as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   0x01, Area Address Type     |   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   0x02, Length of Value       |   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   0x01, Length of Address     |   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   0x00, zero Area Address     |   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.3.  Protocols Supported

   NLPID (Network Layer Protocol ID) 0xC0 has been assigned to TRILL
   [RFC6328].  A Protocols Supported TLV (#129, [RFC1195]) including
   that value appears in TRILL IIH PDUs and LSP number zero PDUs.

4.4.  Link State PDUs (LSPs)

   An LSP number zero MUST NOT be originated larger than 1470 bytes, but
   a larger LSP number zero successfully received MUST be processed and
   forwarded normally.




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4.5.  Originating LSP Buffer Size

   The originatingLSPBufferSize TLV (#14) MUST be in LSP number zero;
   however, if found in other LSP fragments, it is processed normally.
   Should there be more than one originatingLSPBufferSize TLV for an IS,
   the minimum size, but not less than 1470, is used.

5.  IANA Considerations

   This section gives IANA considerations for the TLVs, sub-TLVs, and
   PDUs specified herein.  A number of new code points are assigned, and
   those that were assigned by [RFC6326] are included here for
   convenience.  IANA has replaced all [RFC6326] references in the IANA
   registries with references to this document.

5.1.  TLVs

   This document specifies two IS-IS TLV types -- namely, the Group
   Address TLV (GADDR-TLV; type 142) and the TRILL Neighbor TLV (type
   145).  The PDUs in which these TLVs are permitted for TRILL are shown
   in the table below along with the section of this document where they
   are discussed.  The final "NUMBER" column indicates the permitted
   number of occurrences of the TLV in their PDU, or set of PDUs in the
   case of LSPs, which in these two cases is "*" indicating that the TLV
   MAY occur 0, 1, or more times.

   IANA has registered these two code points in the IANA IS-IS TLV
   registry (ignoring the "Section" and "NUMBER" columns, which are
   irrelevant to that registry).

                        Section TLV IIH LSP SNP Purge NUMBER
                        ======= === === === === ===== ======
     GADDR-TLV            2.1   142  n   y   n    n     *
     TRILL Neighbor TLV   2.5   145  y   n   n    n     *

5.2.  Sub-TLVs

   This document specifies a number of sub-TLVs.  The TLVs in which
   these sub-TLVs occur are shown in the second table below along with
   the section of this document where they are discussed.  The TLVs
   within which these sub-TLVs can occur are determined by the presence
   of an "X" in the relevant column; the column headers are described in
   the first table below.  In some cases, the column header corresponds
   to two different TLVs in which the sub-TLV can occur.







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     Column Head    TLV    RFC      TLV Name
     ===========   =====  ========  ==============
      Grp. Adr.     142    7176      Group Address

      MT Port       143    6165      MT-Port-Cap-TLV

      MT Cap.       242    4971      Router CAPABILITY
                    144    6329      MT-Capability

      Ext. Reach     22    5305      Extended IS Reachability
                    222    5120      MT-ISN

   The final "NUMBER" column below indicates the permitted number of
   occurrences of the sub-TLV cumulatively within all occurrences of
   their TLV(s) in those TLVs' carrying a PDU (or set of PDUs in the
   case of LSPs), as follows:

   0-1 = MAY occur zero or one times.
    1  = MUST occur exactly once.  If absent, the PDU is ignored.  If it
         occurs more than once, results are unspecified.
    *  = MAY occur 0, 1, or more times.

   The values in the "Section" and "NUMBER" columns are irrelevant to
   the IANA sub-registries.

                                sub-   Grp.  MT    MT    Ext.
     Name            Section    TLV#   Adr.  Port  Cap.  Reach  NUMBER
     =================================================================
     GMAC-ADDR        2.1.1       1     X     -     -     -      *
     GIP-ADDR         2.1.2       2     X     -     -     -      *
     GIPV6-ADDR       2.1.3       3     X     -     -     -      *
     GLMAC-ADDR       2.1.4       4     X     -     -     -      *
     GLIP-ADDR        2.1.5       5     X     -     -     -      *
     GLIPV6-ADDR      2.1.6       6     X     -     -     -      *
     VLAN-FLAGS       2.2.1       1     -     X     -     -      1
     Enabled-VLANs    2.2.2       2     -     X     -     -      *
     AppointedFwrdrs  2.2.3       3     -     X     -     -      *
     PORT-TRILL-VER   2.2.4       7     -     X     -     -     0-1
     VLANs-Appointed  2.2.5       8     -     X     -     -      *
     NICKNAME         2.3.2       6     -     -     X     -      *
     TREES            2.3.3       7     -     -     X     -     0-1
     TREE-RT-IDs      2.3.4       8     -     -     X     -      *
     TREE-USE-IDs     2.3.5       9     -     -     X     -      *
     INT-VLAN         2.3.6      10     -     -     X     -      *
     TRILL-VER        2.3.1      13     -     -     X     -     0-1
     VLAN-GROUP       2.3.7      14     -     -     X     -      *
     INT-LABEL        2.3.8      15     -     -     X     -      *
     RBCHANNELS       2.3.9      16     -     -     X     -      *



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     AFFINITY         2.3.10     17     -     -     X     -      *
     LABEL-GROUP      2.3.11     18     -     -     X     -      *
     MTU              2.4        28     -     -     -     X     0-1
     =================================================================
     Name            Section    sub-   Grp.  MT    MT    Ext.   NUMBER
                                TLV#   Adr.  Port  Cap.  Reach

   IANA has entered the newly assigned sub-TLV numbers in the above
   table in the relevant existing sub-TLV registries, as determined by
   which column has an X for that sub-TLV.  For the sub-TLVs from
   NICKNAME through and including VLAN-GROUP, which previously existed
   only in the registry of sub-TLVs under TLV 242, IANA has added each
   sub-TLV with the same sub-TLV number to the existing registry for
   sub-TLVs under TLV 144.

5.3.  PDUs

   The IS-IS PDUs registry remains as established in [RFC6326] except
   that the references to [RFC6326] are updated to reference this
   document.

5.4.  Reserved and Capability Bits

   Any reserved bits (R), bits in reserved fields (RESV), or
   capabilities bits in the PORT-TRILL-VER and TRILL-VER sub-TLVs, which
   are specified herein as "MUST be sent as zero and ignored on receipt"
   or the like, are allocated based on IETF Review [RFC5226].

   Two sub-registries have been created within the TRILL Parameters
   Registry as follows:

      Sub-Registry Name: TRILL-VER Sub-TLV Capability Flags
      Registration Procedures: IETF Review
      Reference: (This document)

       Bit   Description                       Reference
      ===== =============                     ===========
        0    Affinity sub-TLV support.         [Affinity]
        1    FGL-safe                          [RFC7172]
       2-13  Unassigned
      14-31  Extended header flag support.     [RFC7179]










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      Sub-Registry Name: PORT-TRILL-VER Sub-TLV Capability Flags
      Registration Procedures: IETF Review
      Reference: (This document)

       Bit   Description                       Reference
      ===== =============                     ===========
        0    Hello reduction support.          [RFC7180]
       1-2   Unassigned
       3-13  Hop-by-hop extended flag support. [RFC7179]
      14-31  Unassigned

5.5.  TRILL Neighbor Record Flags

   A sub-registry has been created within the TRILL Parameters Registry
   as follows:

      Sub-Registry Name: TRILL Neighbor TLV NEIGHBOR RECORD Flags
      Registration Procedures: Standards Action
      Reference: (This document)

      Bit Short Name   Description            Reference
      ==============  =============          ===========================
       0   Fail       Failed MTU test        [RFC6325][RFC7176][RFC7177]
       1   OOMF       Offering OOMF service  [RFC7180]
      2-7  -          Unassigned

6.  Security Considerations

   For general TRILL protocol security considerations, see the TRILL
   base protocol standard [RFC6325].

   This document raises no new security issues for IS-IS.  IS-IS
   security may be used to secure the IS-IS messages discussed here.
   See [RFC5304] and [RFC5310].  Even when IS-IS authentication is used,
   replays of Hello packets can create denial-of-service conditions; see
   [RFC6039] for details.  These issues are similar in scope to those
   discussed in Section 6.2 of [RFC6325], and the same mitigations may
   apply.

7.  Changes from RFC 6326

   Non-editorial changes from [RFC6326] are summarized in the list
   below:

   1.  Added five sub-TLVs under the Group Address (GADDR) TLV covering
       VLAN-labeled IPv4 and IPv6 addresses and fine-grained-labeled
       MAC, IPv4, and IPv6 addresses (Sections 2.1.2, 2.1.3, 2.1.4,
       2.1.5, and 2.1.6).



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   2.  Added the PORT-TRILL-VER sub-TLV (Section 2.2.4).

   3.  Added the VLANs-Appointed sub-TLV (Section 2.2.5).

   4.  Changed the TRILL-VER sub-TLV as listed below.

       a.  Added 4 bytes of TRILL Header extended flags and capabilities
           supported information.

       b.  Required that the TRILL-VER sub-TLV appear in LSP number
           zero.

       The above changes to TRILL-VER are backward compatible because
       the [RFC6326]-conformant implementations of TRILL thus far have
       only supported version zero and not supported any optional
       capabilities or extended flags, the level of support indicated by
       the absence of the TRILL-VER sub-TLV.  Thus, if an
       [RFC6326]-conformant implementation of TRILL rejects this sub-TLV
       due to the changes specified in this document, it will, at worst,
       decide that support of version zero and no extended flags or
       capabilities is indicated, which is the best an
       [RFC6326]-conformant implementation of TRILL can do anyway.
       Similarly, a TRILL implementation that supports TRILL-VER as
       specified herein and rejects TRILL-VER sub-TLVs in an
       [RFC6326]-conformant TRILL implementation because they are not in
       LSP number zero will decide that the implementation supports only
       version zero with no extended flag or capabilities support, which
       will be correct (Section 2.3.1).

   5.  Clarified the use of invalid VLAN IDs (0x000 and 0xFFF) in the
       Appointed Forwarders sub-TLV and the Interested VLANs and
       Spanning Tree Roots sub-TLV (Sections 2.2.3 and 2.3.6).

   6.  Added the Interested Labels and Spanning Tree Roots sub-TLV to
       indicate attachment of an IS to a fine-grained label [RFC7172]
       analogous to the existing Interested VLANs and Spanning Tree
       Roots sub-TLV for VLANs (Section 2.3.8).

   7.  Added the RBridge Channel Protocols sub-TLV so ISs can announce
       the RBridge Channel protocols they support (Section 2.3.9).

   8.  Permitted specification of the length of the link SNPA field in
       TRILL Neighbor TLVs.  This change is backward compatible because
       the size of 6 bytes is specially encoded as zero, the previous
       value of the bits in the new SIZE field (Section 2.5).






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   9.  Made the size of the MTU PDU Header Probe Source ID and Ack
       Source ID fields be the ID Length from the IS-IS PDU Header
       rather than the fixed value 6 (Section 3).

   10. For robustness, required that LSP number zero PDUs be originated
       as no larger than 1470 bytes but processed regardless of size
       (Section 4.4).

   11. Required that the originatingLSPBufferSize TLV, if present,
       appear in LSP number zero (Section 4.5).

   12. Created sub-registries for and specified the IANA Considerations
       policy for reserved and capability bits in the TRILL version sub-
       TLVs (Section 5.4).

   13. Added the distribution tree Affinity sub-TLV so ISs can request
       distribution tree attachments (Section 2.3.10).

   14. Added the LABEL-GROUP sub-TLV analogous to the VLAN-GROUP sub-TLV
       (Section 2.3.11).

   15. Added multi-topology to permit sub-TLVs previously only in the
       Router Capability TLV to also appear in the MT-Capability TLV and
       to permit the MTU sub-TLV previously limited to the Extended
       Reachability TLV to also appear in the MT-ISN TLV.

   16. Added a sub-registry for Neighbor TLV Neighbor RECORD flag bits
       (Section 5.5).

   17. Explicitly stated that if the number of sources in a GADDR-TLV
       sub-TLV is zero, it indicates a listener for (*,G), that is, a
       listener not restricted by source (Section 2.1).

8.  References

8.1.  Normative References

   [ISO-10589]
              International Organization for Standardization,
              "Intermediate System to Intermediate System intra-domain
              routeing information exchange protocol for use in
              conjunction with the protocol for providing the
              connectionless-mode network service (ISO 8473)", Second
              Edition, November 2002.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, December 1990.




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   [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
              August 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4971]  Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
              "Intermediate System to Intermediate System (IS-IS)
              Extensions for Advertising Router Information", RFC 4971,
              July 2007.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120, February 2008.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, October 2008.

   [RFC6165]  Banerjee, A. and D. Ward, "Extensions to IS-IS for Layer-2
              Systems", RFC 6165, April 2011.

   [RFC6325]  Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
              Ghanwani, "Routing Bridges (RBridges): Base Protocol
              Specification", RFC 6325, July 2011.

   [RFC6328]  Eastlake 3rd, D., "IANA Considerations for Network Layer
              Protocol Identifiers", BCP 164, RFC 6328, July 2011.

   [RFC6329]  Fedyk, D., Ed., Ashwood-Smith, P., Ed., Allan, D., Bragg,
              A., and P. Unbehagen, "IS-IS Extensions Supporting IEEE
              802.1aq Shortest Path Bridging", RFC 6329, April 2012.

   [RFC6439]  Perlman, R., Eastlake, D., Li, Y., Banerjee, A., and F.
              Hu, "Routing Bridges (RBridges): Appointed Forwarders",
              RFC 6439, November 2011.

   [RFC7172]  Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and
              D. Dutt, "Transparent Interconnection of Lots of Links
              (TRILL): Fine-Grained Labeling", RFC 7172, May 2014.

   [RFC7177]  Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, Y., and
              V. Manral, "Transparent Interconnection of Lots of Links
              (TRILL): Adjacency", RFC 7177, May 2014.




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   [RFC7178]  Eastlake 3rd, D., Manral, V., Li, Y., Aldrin, S., and D.
              Ward, "Transparent Interconnection of Lots of Links
              (TRILL): RBridge Channel Support", RFC 7178, May 2014.

   [RFC7179]  Eastlake 3rd, D., Ghanwani, A., Manral, V., Li, Y., and C.
              Bestler, "Transparent Interconnection of Lots of Links
              (TRILL): Header Extension", RFC 7179, May 2014.

   [RFC7180]  Eastlake 3rd, D., Zhang, M., Ghanwani, A., Manral, V., and
              A.  Banerjee, "Transparent Interconnection of Lots of
              Links (TRILL): Clarifications, Corrections, and Updates",
              RFC 7180, May 2014.

8.2.  Informative References

   [Err2869]  RFC Errata, Errata ID 2869, RFC 6326,
              <http://www.rfc-editor.org>.

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, October 2008.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, February 2009.

   [RFC6039]  Manral, V., Bhatia, M., Jaeggli, J., and R. White, "Issues
              with Existing Cryptographic Protection Methods for Routing
              Protocols", RFC 6039, October 2010.

   [RFC6326]  Eastlake, D., Banerjee, A., Dutt, D., Perlman, R., and A.
              Ghanwani, "Transparent Interconnection of Lots of Links
              (TRILL) Use of IS-IS", RFC 6326, July 2011.

   [RFC7042]  Eastlake 3rd, D. and J. Abley, "IANA Considerations and
              IETF Protocol and Documentation Usage for IEEE 802
              Parameters", BCP 141, RFC 7042, October 2013.

   [RFC7175]  Manral, V., Eastlake 3rd, D., Ward, D., and A. Banerjee,
              "Transparent Interconnection of Lots of Links (TRILL):
              Bidirectional Forwarding Detection (BFD) Support", RFC
              7175, May 2014.

   [Affinity] Senevirathne, T., Pathangi, J., and J. Hudson,
              "Coordinated Multicast Trees (CMT) for TRILL", Work in
              Progress, April 2014.






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   [MultiLevel]
              Perlman, R., Eastlake 3rd, D., Ghanwani, A., and H. Zhai,
              "Flexible Multilevel TRILL (Transparent Interconnection of
              Lots of Links)", Work in Progress, January 2014.

   [Resilient]
              Zhang, M. Senevirathne, T., Pathangi, J., Banerjee, A.,
              and A. Ghanwani, "TRILL Resilient Distribution Trees",
              Work in Progress, December 2013.

9.  Acknowledgements

   The authors gratefully acknowledge the contributions and reviews by
   the following individuals: Ross Callon, Spencer Dawkins, Adrian
   Farrel, Alexey Melnikov, Radia Perlman, Carlos Pignataro, and Joe
   Touch.

   The authors also acknowledge the contributions to [RFC6326] by the
   following individuals: Mike Shand, Stewart Bryant, Dino Farinacci,
   Les Ginsberg, Sam Hartman, Dan Romascanu, Dave Ward, and Russ White.
   In particular, thanks to Mike Shand for his detailed and helpful
   comments.





























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Authors' Addresses

   Donald Eastlake 3rd
   Huawei Technologies
   155 Beaver Street
   Milford, MA 01757
   USA

   Phone: +1-508-333-2270
   EMail: d3e3e3@gmail.com


   Tissa Senevirathne
   Cisco Systems
   375 East Tasman Drive,
   San Jose, CA 95134
   USA

   Phone: +1-408-853-2291
   EMail: tsenevir@cisco.com


   Anoop Ghanwani
   Dell
   5450 Great America Parkway
   Santa Clara, CA  95054
   USA

   EMail: anoop@alumni.duke.edu


   Dinesh Dutt
   Cumulus Networks
   1089 West Evelyn Avenue
   Sunnyvale, CA 94086
   USA

   EMail: ddutt.ietf@hobbesdutt.com


   Ayan Banerjee
   Insieme Networks
   210 West Tasman Drive
   San Jose, CA 95134
   USA

   EMail: ayabaner@gmail.com




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