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RFC 7961

Proposed STD
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Transparent Interconnection of Lots of Links (TRILL): Interface Addresses APPsub-TLV

 


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Internet Engineering Task Force (IETF)                   D. Eastlake 3rd
Request for Comments: 7961                                         Y. Li
Category: Standards Track                                         Huawei
ISSN: 2070-1721                                              August 2016


         Transparent Interconnection of Lots of Links (TRILL):
                     Interface Addresses APPsub-TLV

Abstract

   This document specifies a TRILL (Transparent Interconnection of Lots
   of Links) IS-IS application sub-TLV that enables the reporting by a
   TRILL switch of sets of addresses.  Each set of addresses reports all
   of the addresses that designate the same interface (port) and also
   reports the TRILL switch by which that interface is reachable.  For
   example, a 48-bit MAC (Media Access Control) address, IPv4 address,
   and IPv6 address can be reported as all corresponding to the same
   interface reachable by a particular TRILL switch.  Such information
   could be used in some cases to synthesize responses to, or bypass the
   need for, the Address Resolution Protocol (ARP), the IPv6 Neighbor
   Discovery (ND) protocol, or the flooding of unknown MAC addresses.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7961.

[Page 2] 
Copyright Notice

   Copyright (c) 2016 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 ..........................3
   2. Format of the Interface Addresses APPsub-TLV ....................4
   3. IA APPsub-TLV Sub-sub-TLVs ......................................9
      3.1. AFN Size Sub-sub-TLV ......................................10
      3.2. Fixed Address Sub-sub-TLV .................................11
      3.3. Data Label Sub-sub-TLV ....................................12
      3.4. Topology Sub-sub-TLV ......................................12
   4. Security Considerations ........................................13
   5. IANA Considerations ............................................14
      5.1. Allocation of AFN Values ..................................14
      5.2. IA APPsub-TLV Sub-sub-TLVs Sub-registry ...................15
      5.3. IA APPsub-TLV Number ......................................16
   6. Additional AFN Information .....................................16
   7. Processing Address Sets ........................................16
   8. References .....................................................18
      8.1. Normative References ......................................18
      8.2. Informative References ....................................20
   Appendix A. Examples ..............................................21
      A.1. Simple Example ............................................21
      A.2. Complex Example ...........................................22
   Acknowledgments ...................................................24
   Authors' Addresses ................................................24

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1.  Introduction

   This document specifies a TRILL (Transparent Interconnection of Lots
   of Links) [RFC6325] IS-IS application sub-TLV (APPsub-TLV) [RFC6823]
   that enables the convenient representation of sets of addresses where
   all of the addresses in each set designate the same interface (port).
   For example, a 48-bit MAC (Media Access Control) [RFC7042] address,
   IPv4 address, and IPv6 address can be reported as all three
   designating the same interface.  In addition, a Data Label (VLAN or
   Fine-Grained Label (FGL) [RFC7172]) is specified for the interface,
   along with the TRILL switch and, optionally, the TRILL switch port
   from which the interface is reachable.  Such information could be
   used in some cases to synthesize responses to, or bypass the need
   for, the Address Resolution Protocol (ARP) [RFC826], the IPv6
   Neighbor Discovery (ND) [RFC4861] protocol, the Reverse Address
   Resolution Protocol (RARP) [RFC903], or the flooding of unknown
   destination MAC addresses [ARPND].  If the information reported is
   complete, it can also be used to detect and discard packets with
   forged source addresses.

   This APPsub-TLV appears inside the TRILL GENINFO TLV specified in the
   End Station Address Distribution Information (ESADI) RFC [RFC7357]
   but may also occur in other application contexts.  The
   "directory assistance" TRILL Edge services [DirectoryScheme] are
   expected to make use of this APPsub-TLV.

   Although in some IETF protocols address field types are represented
   by an Ethertype [RFC7042] or a hardware address type [RFC5494], only
   the Address Family Number (AFN) is used in this APPsub-TLV to
   represent the address field type.

1.1.  Conventions Used in This Document

   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].
   Capitalized IANA-related terms such as "Expert Review" are to be
   interpreted as described in [RFC5226].

   The terminology and acronyms of [RFC6325] are used herein, along with
   the following additional acronyms and terms:

   AFN: Address Family Number
      (http://www.iana.org/assignments/address-family-numbers/)

   APPsub-TLV: Application sub-TLV [RFC6823]

   Data Label: VLAN or FGL

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   FGL: Fine-Grained Label [RFC7172]

   IA: Interface Address(es)

   MAC: Media Access Control

   Nickname: A 16-bit TRILL switch identifier, as specified in
      Section 3.7 of [RFC6325] and as updated by Section 4 of [RFC7780]

   RBridge: An alternative name for a TRILL switch

   TRILL switch: A device that implements the TRILL protocol

2.  Format of the Interface Addresses APPsub-TLV

   The Interface Addresses (IA) APPsub-TLV is used to advertise a set of
   addresses indicating the same interface (port) within a Data Label
   (VLAN or FGL).  It also associates that interface with the TRILL
   switch and, optionally, the TRILL switch port by which the interface
   is reachable.  These addresses can be in different address families.
   For example, the IA APPsub-TLV can be used to declare that a
   particular interface with specified IPv4, IPv6, and 48-bit MAC
   addresses in some particular Data Label is reachable from a
   particular TRILL switch.  While those three types of addresses are
   likely to be the only types of interest, any address type for which
   an AFN has been assigned by IANA can be represented.

   The Template field in a particular IA APPsub-TLV indicates the format
   of each Address Set it carries.  Certain well-known sets of addresses
   are represented by special values.  Other sets of addresses are
   specified by a list of AFNs.  The Template format that uses a list of
   AFNs provides an explicit pattern for the type and order of addresses
   in each Address Set in the IA APPsub-TLV that includes that Template.

   A device or application making use of IA APPsub-TLV data is not
   required to make use of all IA data.  For example, a device or
   application that was only interested in MAC and IPv6 addresses could
   ignore any IPv4 or other types of address information that was
   present.

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   Figure 1 shows an IA APPsub-TLV as it would appear inside an IS-IS
   Flooding Scope Link State PDU (FS-LSP) using an extended flooding
   scope [RFC7356] TLV -- for example, in ESADI [RFC7357].  Within an
   IS-IS FS-LSP using traditional [ISO-10589] TLVs, the Type and Length
   would be 1-byte unsigned integers equal to or less than 255, but with
   an extended TLV, the Type and Length are 2-byte unsigned integers.

          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          | Type = (10)                   |  (2 bytes)
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          | Length                        |  (2 bytes)
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          | Addr Sets End                 |  (2 bytes)
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          | Nickname                      |  (2 bytes)
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          | Flags         |                  (1 byte)
          +-+-+-+-+-+-+-+-+
          | Confidence    |                  (1 byte)
          +-+-+-+-+-+-+-+-+-+-
          | Template ...                     (variable)
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
          | Address Set 1    (size determined by Template)    |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
          | Address Set 2    (size determined by Template)    |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
          |   ...
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
          | Address Set N    (size determined by Template)    |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
          | optional sub-sub-TLVs ...
          +-+-+-+-+-+-+-+-+-+-+-+-...

                 Figure 1: Interface Addresses APPsub-TLV

   o  Type: Interface Addresses TRILL APPsub-TLV type; set to 10
      (IA-SUBTLV).

   o  Length: Variable; minimum 7.  If Length is 6 or less or if the
      APPsub-TLV extends beyond the size of an encompassing TRILL
      GENINFO TLV or other context, the APPsub-TLV MUST be ignored.  For
      manageability, a counter reflecting the receipt of such malformed
      IA APPsub-TLVs should be maintained.

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   o  Addr Sets End: The unsigned integer byte number, within the IA
      APPsub-TLV value part, of the last byte of the last Address Set,
      where the first byte is numbered 1.  This will be the number of
      the byte just before the first sub-sub-TLV if any sub-sub-TLVs are
      present (see Section 3).  The processing is as follows:

      -  If this field is greater than Length or points to before the
         end of the Template, the IA APPsub-TLV is corrupt and MUST be
         discarded.

      -  If this field is equal to Length, there are no sub-sub-TLVs.

      -  If this field is less than Length, sub-sub-TLVs are parsed as
         specified in Section 3.

      Note: This field is always 2 bytes in size.

   o  Nickname: The nickname (see Section 1.1) of the TRILL switch by
      which the Address Sets are reachable.  If 0, the Address Sets are
      reachable from the TRILL switch originating the message containing
      the APPsub-TLV (for example, an ESADI [RFC7357] message).

   o  Flags: A byte of flags, as follows:

          0 1 2 3 4 5 6 7
         +-+-+-+-+-+-+-+-+
         |D|L|   RESV    |
         +-+-+-+-+-+-+-+-+

         D: Directory flag: If D is 1, the APPsub-TLV contains directory
            information [RFC7067].

         L: Local flag: If L is 1, the APPsub-TLV contains information
            learned locally by observing ingressed frames [RFC6325].
            (Both D and L can be set to 1 in the same IA APPsub-TLV if a
            TRILL switch had learned an address locally and also
            advertised it as a directory.)

         RESV: Additional reserved flag bits that MUST be sent as zero
            and ignored on receipt.

   o  Confidence: This 8-bit unsigned quantity in the range 0 to 254
      indicates the confidence level in the addresses being transported
      (see Section 4.8.2 of [RFC6325]).  A value of 255 is treated as if
      it was 254.

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   o  Template: The initial byte of this field is the unsigned integer
      K.  If K has a value from 1 to 31, it indicates that this initial
      byte is followed by a list of K AFNs that specify the exact
      structure and order of each Address Set occurring later in the
      APPsub-TLV.  K can be 1, which is the minimum valid value.  If K
      is 0, the IA APPsub-TLV is ignored.  If K is 32 to 254, the length
      of the Template field is 1 byte, and its value is intended to
      correspond to a particular ordered set of AFNs, some of which are
      specified below.  The value of 255 for K is reserved for future
      definition and causes the IA APPsub-TLV to be ignored.

      If the Template uses explicit AFNs, it looks like the following,
      with the number of AFNs, up to 31, equal to K.

            +-+-+-+-+-+-+-+-+
            |  K            |                  (1 byte)
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |  AFN 1                        |  (2 bytes)
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |  AFN 2                        |  (2 bytes)
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |   ...
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |  AFN K                        |  (2 bytes)
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      For K in the range 32 to 39, values indicate a specific sequence,
      as specified below.  The values of K from 40 to 254 are reserved
      for future specification.  If the value of K is not understood by
      a receiver of the IA-APPsub-TLV, any Address Sets present are
      ignored.

             K   Addresses in order of occurrence
            ---  --------------------------------
             32  48-bit MAC
             33  48-bit MAC, IPv4
             34  48-bit MAC, IPv6
             35  48-bit MAC, IPv4, IPv6
             36  48-bit MAC, RBridge port
             37  48-bit MAC, IPv4, RBridge port
             38  48-bit MAC, IPv6, RBridge port
             39  48-bit MAC, IPv4, IPv6, RBridge port

      For ease of decoding, note that for values of K between 32 and 39
      inclusive, the 0x01 bit indicates that an IPv4 address is present,
      the 0x02 bit indicates that an IPv6 address is present, and the
      0x04 bit indicates that an RBridge Port ID is present.

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   o  AFN: A 2-byte Address Family Number.  The number of AFNs present
      is given by K, except that there are no AFNs if K is greater than
      31.  The AFN sequence specifies the structure of the Address Sets
      occurring later in the TLV.  For example, if the Template size is
      2 and the two AFNs present are the AFNs for a 48-bit MAC and an
      IPv4 address, in that order, then each Address Set present will
      consist of a 6-byte MAC address followed by a 4-byte IPv4 address.
      If any AFNs are present that are unknown to the receiving IS and
      the length of the corresponding address is not provided by a
      sub-sub-TLV as specified below, the receiving IS will be unable to
      parse the Address Sets and MUST ignore the IA APPsub-TLV.

   o  Address Set: Each Address Set in the APPsub-TLV consists of
      exactly the same sequence of addresses and types as specified by
      the Template earlier in the APPsub-TLV.  No alignment, other than
      to a byte boundary, is provided.  The addresses in each Address
      Set are contiguous with no unused bytes between them, and the
      Address Sets are contiguous with no unused bytes between
      successive Address Sets.  The Address Sets must fit within the
      TLV.  See Section 7 on interpreting certain Address Sets.

   o  sub-sub-TLVs: If the Address Sets indicated by Addr Sets End do
      not completely fill the length of the APPsub-TLV (as indicated by
      the Length field), then per Section 4 of [RFC5305] the remaining
      bytes are parsed as sub-sub-TLVs.  Any such sub-sub-TLVs that are
      not known to the receiving TRILL switch are ignored.  Should this
      parsing not be possible -- for example, there is only one
      remaining byte or an apparent sub-sub-TLV extends beyond the end
      of the TLV -- the containing IA APPsub-TLV is considered corrupt
      and is ignored.  (Several sub-sub-TLV types are specified in
      Section 3.)

   Different IA APPsub-TLVs within the same or different LSPs or other
   data structures may have different Templates.  The same AFN may occur
   more than once in a Template, and the same address may occur in
   different Address Sets.  For example, a 48-bit MAC address interface
   might have three different IPv6 addresses.  This could be represented
   by an IA APPsub-TLV whose Template specifically provided for one
   EUI-48 address and three IPv6 addresses; this might be an efficient
   format if there were multiple interfaces with that pattern.
   Alternatively, a Template with one 48-bit MAC and one IPv6 address
   could be used in an IA APPsub-TLV with three Address Sets each having
   the same MAC address but different IPv6 addresses; this might be the
   most efficient format if only one interface had multiple IPv6
   addresses and other interfaces had only one IPv6 address.

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   In order to be able to parse the Address Sets, a receiving TRILL
   switch must know at least the size of the address for each AFN or
   address type the Template specifies; however, the presence of the
   Addr Sets End field means that the sub-sub-TLVs, if any, can always
   be located by a receiver.  A TRILL switch can be assumed to know the
   size of the AFNs mentioned in Section 5.  Should a TRILL switch wish
   to include an AFN that some receiving TRILL switch in the campus may
   not know, it SHOULD include an AFN Size sub-sub-TLV as described in
   Section 3.1.  If an IA APPsub-TLV is received with one or more AFNs
   in its Template for which the receiving TRILL switch does not know
   the length and for which an AFN Size sub-sub-TLV is not present, that
   IA APPsub-TLV MUST be ignored.

   For manageability, a counter of ill-formed IA APPsub-TLVs received
   and ignored due to unknown K, unknown AFN, and the like (as described
   above) should be maintained.

3.  IA APPsub-TLV Sub-sub-TLVs

   IA APPsub-TLVs can have sub-sub-TLVs (sub-TLVs of sub-TLVs [RFC5305])
   at the end, as specified below.  These sub-sub-TLVs occur after the
   Address Sets.  The amount of space available for sub-sub-TLVs is
   determined from the overall IA APPsub-TLV length and the value of the
   Addr Sets End byte.

   There is no ordering restriction on sub-sub-TLVs.  Unless otherwise
   specified, each sub-sub-TLV type can occur zero, one, or many times
   in an IA APPsub-TLV.  Any sub-sub-TLVs for which the Type is unknown
   are ignored.  For manageability, a counter of sub-sub-TLVs received
   and ignored due to an unknown Type or other reasons, as described
   below, should be maintained.

   The data structures of the sub-sub-TLVs shown below, with 2-byte
   Types and Lengths, assume that the enclosing IA APPsub-TLV is in an
   extended LSP TLV [RFC7356] or some non-LSP context.  If they were
   used in an IA APPsub-TLV in a non-extended LSP [ISO-10589], then only
   1-byte Types and Lengths could be used.  As a result, any sub-sub-TLV
   types greater than 255 could not be used, and Length would be limited
   to 255.

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3.1.  AFN Size Sub-sub-TLV

   Using this sub-sub-TLV, the originating TRILL switch can specify the
   size of an address type.  This is useful under the following two
   circumstances:

   1. One or more AFNs that are unknown to the receiving TRILL switch
      appear in the Template.  If an AFN Size sub-sub-TLV is present for
      each such AFN, then at least the IA APPsub-TLV can be parsed, and
      possibly other addresses in each Address Set can still be used.

   2. If an AFN occurs in the Template that represents a variable-length
      address, this sub-sub-TLV gives its size for all occurrences in
      that IA APPsub-TLV.

       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Type = AFNsz                  |  (2 bytes)
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Length                        |  (2 bytes)
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | AFN Size Record 1                             |  (3 bytes)
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | AFN Size Record 2                             |  (3 bytes)
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | ...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | AFN Size Record N                             |  (3 bytes)
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 2: AFN Size Sub-sub-TLV

   Where each AFN Size Record is structured as follows:

         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |  AFN                          |  (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |  AdrSize      |                  (1 byte)
         +-+-+-+-+-+-+-+-+

   o  Type: AFN Size sub-sub-TLV type; set to 1 (AFNsz).

   o  Length: 3*N, where N is the number of AFN Size Records present.
      If Length is not a multiple of 3, the sub-sub-TLV MUST be ignored.

   o  AFN Size Record(s): Zero or more 3-byte records, each giving the
      size of an address type identified by an AFN.

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   o  AFN: The AFN whose length is being specified by the AFN Size
      Record.

   o  AdrSize: The length, in bytes, of addresses specified by the AFN
      field as an unsigned integer.

   An AFN Size sub-sub-TLV for any AFN known to the receiving TRILL
   switch is compared with the size known to the TRILL switch.  If they
   differ, the IA APPsub-TLV is assumed to be corrupt and MUST be
   ignored.

3.2.  Fixed Address Sub-sub-TLV

   There may be cases where, in a particular IA APPsub-TLV, the same
   address would appear in every Address Set across the IA APPsub-TLV.
   To avoid wasted space, this sub-sub-TLV can be used to indicate such
   a fixed address.  The address or addresses incorporated into the sets
   by this sub-sub-TLV are NOT mentioned in the IA APPsub-TLV Template.

         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         | Type = FIXEDADR               | (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         | Length                        | (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         | AFN                           | (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         | Fixed Address                   (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-...

                    Figure 3: Fixed Address Sub-sub-TLV

   o  Type: Data Label sub-sub-TLV type; set to 2 (FIXEDADR).

   o  Length: Variable; minimum 2.  If Length is 0 or 1, the sub-sub-TLV
      MUST be ignored.

   o  AFN: Address Family Number of the Fixed Address.

   o  Fixed Address: The address of the Type indicated by the preceding
      AFN field that is considered to be part of every Address Set in
      the IA APPsub-TLV.

   The Length field implies a size for the Fixed Address.  If that size
   differs from the size of the address type for the given AFN as known
   by the receiving TRILL switch, the Fixed Address sub-sub-TLV is
   considered corrupt and MUST be ignored.

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3.3.  Data Label Sub-sub-TLV

   This sub-sub-TLV indicates the Data Label within which the interfaces
   listed in the IA APPsub-TLV are reachable.  It is useful if the IA
   APPsub-TLV occurs outside of the context of a message specifying the
   Data Label or if it is desired and permitted to override that
   specification.  Multiple occurrences of this sub-sub-TLV indicate
   that the interfaces are reachable in all of the Data Labels given.

         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |Type = DATALEN                 | (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         | Length                        | (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         | Data Label                      (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-...

                     Figure 4: Data Label Sub-sub-TLV

   o  Type: Data Label sub-TLV type; set to 3 (DATALEN).

   o  Length: 2 or 3.  If Length is some other value, the sub-sub-TLV
      MUST be ignored.

   o  Data Label: If Length is 2, the bottom 12 bits of the Data Label
      are a VLAN ID and the top 4 bits are reserved (MUST be sent as
      zero and ignored on receipt).  If Length is 3, the three Data
      Label bytes contain an FGL [RFC7172].

3.4.  Topology Sub-sub-TLV

   The presence of this sub-sub-TLV indicates that the interfaces given
   in the IA APPsub-TLV are reachable in the topology given.  It is
   useful if the IA APPsub-TLV occurs outside of the context of a
   message indicating the topology or if it is desired and permitted to
   override that specification.  If it occurs multiple times, then the
   Address Sets are in all of the topologies given.

         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |Type = TOPOLOGY                |  (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         | Length                        |  (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         | RESV  |        Topology       |  (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 5: Topology Sub-sub-TLV

Top      ToC       Page 13 
   o  Type: Topology sub-TLV type; set to 4 (TOPOLOGY).

   o  Length: 2.  If Length is some other value, the sub-sub-TLV MUST be
      ignored.

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

   o  Topology: The 12-bit topology number [RFC5120].

4.  Security Considerations

   The integrity of address mapping and reachability information as well
   as the correctness of Data Labels (VLANs or FGLs [RFC7172]) are very
   important.  Forged, altered, or incorrect address mapping or data
   labeling can lead to delivery of packets to the incorrect party,
   violating security policy.  However, this document merely describes a
   data format and does not provide any explicit mechanisms for securing
   that information, other than a few simple consistency checks that
   might detect some corrupted data.  Security on the wire, or in
   storage, for this data is to be provided by the transport or storage
   used.  For example, when transported with ESADI [RFC7357] or RBridge
   Channel [RFC7178], ESADI security or Channel Tunnel [ChannelTunnel]
   security mechanisms can be used, respectively.

   The address mapping and reachability information, if known to be
   complete and correct, can be used to detect some cases of forged
   packet source addresses [RFC7067].  In particular, if native traffic
   from an end station is received by a TRILL switch that would
   otherwise accept it but authoritative data indicates that the source
   address should not be reachable from the receiving TRILL switch, that
   traffic should be discarded.  The data format specified in this
   document may optionally include a TRILL switch Port ID number so that
   this forged address filtering can be optionally applied with port
   granularity.  For manageability, a counter of frames so discarded
   should be maintained.

   See [RFC6325] for general TRILL security considerations.

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5.  IANA Considerations

   The following subsections specify IANA allocations.

5.1.  Allocation of AFN Values

   IANA has allocated values in the "Address Family Numbers" registry
   that may be useful for IA APPsub-TLVs.  The values are as follows:

        Hex    Decimal   Description      References
       -----   -------   -----------      ----------
        0001        1    IPv4
        0002        2    IPv6
        4005    16389    48-bit MAC       Section 2.1 of [RFC7042]
        4006    16390    64-bit MAC       Section 2.2 of [RFC7042]
        4007    16391    OUI              Section 6 of RFC 7961
        4008    16392    MAC/24           Section 6 of RFC 7961
        4009    16393    MAC/40           Section 6 of RFC 7961
        400A    16394    IPv6/64          Section 6 of RFC 7961
        400B    16395    RBridge Port ID  Section 6 of RFC 7961

   Other AFNs can be found at <http://www.iana.org/assignments/
   address-family-numbers>.

   See Section 7 on interpreting Address Sets.

Top      ToC       Page 15 
5.2.  IA APPsub-TLV Sub-sub-TLVs Sub-registry

   IANA has established a new sub-registry of the "Transparent
   Interconnection of Lots of Links (TRILL) Parameters" registry for
   sub-sub-TLVs of the Interface Addresses APPsub-TLV, with the
   following initial contents:

      Name:  Interface Addresses APPsub-TLV Sub-sub-TLVs

      Procedure:  Expert Review

      Note:  Types greater than 255 are not usable in some contexts.

      Reference:  RFC 7961

          Type      Description       Reference
         ------     -----------       ---------
             0      Reserved          RFC 7961
             1      AFN Size          RFC 7961
             2      Fixed Address     RFC 7961
             3      Data Label        RFC 7961
             4      Topology          RFC 7961
         5-254      Unassigned
           255      Reserved          RFC 7961
     256-65534      Unassigned
         65535      Reserved          RFC 7961

   Expert Guidance: A designated expert for this registry should decide
      whether to permit the assignment of a type based on clear
      documentation of the proposed type as provided by the requester,
      such as a complete Internet-Draft.  New types should not duplicate
      existing types.  Requests should indicate whether a type less than
      255 is desired; such types can be used in contexts where only
      1 byte of a type (and usually only 1 byte of the length) is
      permitted.  Types greater than 255 can only be used where 2-byte
      types are allowed, such as in Extended Level 1 Flooding Scope
      (E-L1FS) or Extended Level 1 Circuit Scope (E-L1CS) extended
      FS-LSPs [RFC7356]; in those contexts, lengths up to 65535 bytes
      can also be expressed, although they may not be usable if the
      resulting TLV would not fit into a larger context restricted by an
      MTU setting or the like.  Values within the region below 255 and
      the region above 255 should be allocated sequentially, unless
      there is an extraordinary reason for a special value.

Top      ToC       Page 16 
5.3.  IA APPsub-TLV Number

   IANA has allocated type 10 as the IA APPsub-TLV in the "TRILL
   APPsub-TLV Types under IS-IS TLV 251 Application Identifier 1"
   registry from the range under 256.  In the registry, the name is "IA"
   and the reference is this document.

6.  Additional AFN Information

   This section provides additional information concerning AFNs that
   were allocated in connection with this document.  These AFNs are not
   restricted to use in the IA APPsub-TLV and may be used in other
   protocols where they would be appropriate.

   OUI: A 3-byte (24-bit) Organizationally Unique Identifier used as the
      initial 3 bytes of a MAC address.  See Sections 2.1 and 2.2 of
      [RFC7042], and Section 7 below.

   MAC/24: A 3-byte (24-bit) quantity used as the final 3 bytes of a
      48-bit MAC address.  See Section 2.1 of [RFC7042] and Section 7
      below.

   MAC/40: A 5-byte (40-bit) quantity used as the final 5 bytes of a
      64-bit MAC address.  See Section 2.2 of [RFC7042] and Section 7
      below.

   IPv6/64: An 8-byte (64-bit) quantity used as the initial 8 bytes of
      an IPv6 address.  See Section 7 below.

   RBridge Port ID: A 16-bit quantity that uniquely identifies a port on
      a TRILL switch (RBridge).  See Section 4.4.2 of [RFC6325].

7.  Processing Address Sets

   The following processes should be followed in interpreting sets of
   AFN values in an IA APPsub-TLV to synthesize addresses.  These apply
   whether the AFN values came from sub-sub-TLVs, appeared within an
   Address Set, or came from both sources.  In general, the processing
   is applied separately to each Address Set as supplemented by any
   Fixed Address sub-sub-TLVs that are present.

   The OUI AFN value is provided so that MAC addresses can be
   abbreviated if they have the same upper 24 bits.  A MAC/24 is a
   24-bit suffix intended to be prefixed by an OUI to create a 48-bit
   MAC address [RFC7042]; in the absence of an OUI, a MAC/24 entry
   cannot be used.  A MAC/40 is a 40-bit suffix intended to be prefixed
   by an OUI to create a 64-bit MAC address [RFC7042]; in the absence of
   an OUI, a MAC/40 entry cannot be used.

Top      ToC       Page 17 
   Typically, an OUI would be provided as a Fixed Address sub-sub-TLV
   (see Section 3.2) using the OUI AFN, but there is no prohibition
   against one or more OUIs appearing in an Address Set.

   Each Address Set, after being supplemented by any Fixed Address
   sub-sub-TLVs, is processed by combining each OUI in the Address Set
   with each MAC/24 and each MAC/40 address in the Address Set.
   Depending on how many of each of these address types are present,
   zero or more 48-bit and/or 64-bit MAC addresses may be synthesized
   that are subsequently processed as if they had been part of the
   Address Set.  If there are no MAC/24 or MAC/40 addresses present, any
   OUIs are ignored.  If there are no OUIs, any MAC/24s and/or MAC/40s
   are ignored.  If there are K1 OUIs, K2 MAC/24s, and K3 MAC/40s, K1*K2
   48-bit MACs are synthesized and K1*K3 64-bit MACs are synthesized.

   IPv6/64 is an 8-byte quantity that is the first 64 bits of an IPv6
   address.  IPv6/64s are ignored unless, after the processing described
   above in this subsection, there are one or more 48-bit and/or 64-bit
   MAC addresses in the Address Set to provide the lower 64 bits of the
   IPv6 address.  For this purpose, a 48-bit MAC address is expanded to
   64 bits as described in Section 2.2.1 of [RFC7042].  If there are K4
   IPv6/64s present and K5 48-bit and 64-bit MAC addresses present,
   K4*K5 128-bit IPv6 addresses are synthesized.

   Synthesized addresses are treated as if they had been members of the
   Address Set.

Top      ToC       Page 18 
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)",
              ISO Standard 10589, 2002.

   [RFC826]   Plummer, D., "Ethernet Address Resolution Protocol: Or
              Converting Network Protocol Addresses to 48.bit Ethernet
              Address for Transmission on Ethernet Hardware", STD 37,
              RFC 826, DOI 10.17487/RFC0826, November 1982,
              <http://www.rfc-editor.org/info/rfc826>.

   [RFC903]   Finlayson, R., Mann, T., Mogul, J., and M. Theimer, "A
              Reverse Address Resolution Protocol", STD 38, RFC 903,
              DOI 10.17487/RFC0903, June 1984,
              <http://www.rfc-editor.org/info/rfc903>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <http://www.rfc-editor.org/info/rfc4861>.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS:
              Multi Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <http://www.rfc-editor.org/info/rfc5120>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305,
              October 2008, <http://www.rfc-editor.org/info/rfc5305>.

Top      ToC       Page 19 
   [RFC6325]  Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
              Ghanwani, "Routing Bridges (RBridges): Base Protocol
              Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011,
              <http://www.rfc-editor.org/info/rfc6325>.

   [RFC6823]  Ginsberg, L., Previdi, S., and M. Shand, "Advertising
              Generic Information in IS-IS", RFC 6823,
              DOI 10.17487/RFC6823, December 2012,
              <http://www.rfc-editor.org/info/rfc6823>.

   [RFC7042]  Eastlake 3rd, D. and J. Abley, "IANA Considerations and
              IETF Protocol and Documentation Usage for IEEE 802
              Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
              October 2013, <http://www.rfc-editor.org/info/rfc7042>.

   [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,
              DOI 10.17487/RFC7172, May 2014,
              <http://www.rfc-editor.org/info/rfc7172>.

   [RFC7356]  Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
              Scope Link State PDUs (LSPs)", RFC 7356,
              DOI 10.17487/RFC7356, September 2014,
              <http://www.rfc-editor.org/info/rfc7356>.

   [RFC7357]  Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O.
              Stokes, "Transparent Interconnection of Lots of Links
              (TRILL): End Station Address Distribution Information
              (ESADI) Protocol", RFC 7357, DOI 10.17487/RFC7357,
              September 2014, <http://www.rfc-editor.org/info/rfc7357>.

   [RFC7780]  Eastlake 3rd, D., Zhang, M., Perlman, R., Banerjee, A.,
              Ghanwani, A., and S. Gupta, "Transparent Interconnection
              of Lots of Links (TRILL): Clarifications, Corrections, and
              Updates", RFC 7780, DOI 10.17487/RFC7780, February 2016,
              <http://www.rfc-editor.org/info/rfc7780>.

Top      ToC       Page 20 
8.2.  Informative References

   [ARPND]    Li, Y., Eastlake 3rd, D., Dunbar, L., and R. Perlman,
              "TRILL: ARP/ND Optimization", Work in Progress,
              draft-ietf-trill-arp-optimization-06, April 2016.

   [ChannelTunnel]
              Eastlake 3rd, D., Umair, M., and Y. Li, "TRILL: RBridge
              Channel Header Extension", Work in Progress,
              draft-ietf-trill-channel-tunnel-11, August 2016.

   [DirectoryScheme]
              Eastlake 3rd, D., Dunbar, L., Perlman, R., and Y. Li,
              "TRILL: Edge Directory Assist Mechanisms", Work in
              Progress, draft-ietf-trill-directory-assist-mechanisms-07,
              February 2016.

   [RFC5494]  Arkko, J. and C. Pignataro, "IANA Allocation Guidelines
              for the Address Resolution Protocol (ARP)", RFC 5494,
              DOI 10.17487/RFC5494, April 2009,
              <http://www.rfc-editor.org/info/rfc5494>.

   [RFC7067]  Dunbar, L., Eastlake 3rd, D., Perlman, R., and I.
              Gashinsky, "Directory Assistance Problem and High-Level
              Design Proposal", RFC 7067, DOI 10.17487/RFC7067,
              November 2013, <http://www.rfc-editor.org/info/rfc7067>.

   [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,
              DOI 10.17487/RFC7178, May 2014,
              <http://www.rfc-editor.org/info/rfc7178>.

Top      ToC       Page 21 
Appendix A.  Examples

   Below are example IA APPsub-TLVs.  "0x" indicates that the quantity
   is in hexadecimal.  "0b" indicates that the quantity is in binary.
   Leading zeros are retained.

A.1.  Simple Example

   Below is an annotated IA APPsub-TLV carrying two simple pairs of
   EUI-48 MAC addresses and IPv4 addresses from a Push Directory
   (a directory conforming to the Push Model [RFC7067]).  No
   sub-sub-TLVs are included.

         0x0002(10)   Type: Interface Addresses
         0x001B        Length: 27 (= 0x1B)
         0x001B        Address Sets End: 27 (= 0x1B)
         0x1234        RBridge Nickname from which reachable
         0b10000000    Flags: Push Directory data
         0xE3          Confidence = 227
         33            Template: 33 (0x21) = 32 + 1(IPv4)

               Address Set One
         0x00005E0053A9   48-bit MAC address
         198.51.100.23    IPv4 address

               Address Set Two
         0x00005E00536B   48-bit MAC address
         203.0.113.201    IPv4 address

   The size includes 7 for the fixed fields through and including the
   1-byte Template, plus 2 times the Address Set size.  Each Address Set
   is 10 bytes: 6 for the 48-bit MAC address plus 4 for the IPv4
   address.  Therefore, the total size is 7 + 2*10 = 27.

   See Section 2 for more information on the Template.

Top      ToC       Page 22 
A.2.  Complex Example

   Below is an annotated IA APPsub-TLV carrying three sets of addresses,
   each consisting of an EUI-48 MAC address, an IPv4 address, an IPv6
   address, and an RBridge Port ID, all from a Push Directory
   (a directory conforming to the Push Model [RFC7067]).  The IPv6
   address for each Address Set is synthesized from the MAC address
   given in that set and the IPv6/64 64-bit prefix provided through a
   Fixed Address sub-sub-TLV.  In addition, a sub-sub-TLV is included
   that provides an FGL that overrides whatever Data Label may be
   provided by the envelope (for example, an ESADI-LSP [RFC7357]) within
   which this IA APPsub-TLV occurs.

       0x0002(10)    Type: Interface Addresses
       0x0036        Length: 64 (= 0x40)
       0x0021        Address Sets End: 43 (= 0x2B)
       0x4321        RBridge Nickname from which reachable
       0b10000000    Flags: Push Directory data
       0xD3          Confidence = 211
       37            Template: 37(0x25) = 32 + 1(IPv4) + 4(Port)

             Address Set One
       0x00005E0053DE   48-bit MAC address
       198.51.100.105   IPv4 address
       0x1DE3           RBridge Port ID

             Address Set Two
       0x00005E0053E3   48-bit MAC address
       203.0.113.89     IPv4 address
       0x1DEE           RBridge Port ID

             Address Set Three
       0x00005E0053D3   48-bit MAC address
       192.0.2.139      IPv4 address
       0x01DE           RBridge Port ID

             sub-sub-TLV One
       0x0003           Type: Data Label
       0x0003           Length: Implies FGL
       0xD3E3E3         Fine-Grained Label

             sub-sub-TLV Two
       0x0002           Type: Fixed Address
       0x000A           Size: 0x0A = 10
       0x400A           AFN: IPv6/64
       0x20010db800000000   IPv6 Prefix: 2001:db8::

   See Section 2 for more information on the Template.

Top      ToC       Page 23 
   The Fixed Address sub-sub-TLV causes the IPv6/64 value given to be
   treated as if it occurred as a fourth entry inside each of the three
   Address Sets.  When there is an IPv6/64 entry and a 48-bit MAC entry,
   the MAC value is expanded by inserting 0xfffe immediately after the
   OUI, and the local/global bit is inverted.  The resulting
   Modified EUI-64-bit value is used as the lower 64 bits of the
   resulting IPv6 address (Section 2.2.1 of [RFC7042]).  As a result, a
   receiving TRILL switch would treat the three Address Sets shown as if
   they had an IPv6 address in them, as follows:

               Address Set One
         0x20010db80000000002005efffe0053de  IPv6 Address

               Address Set Two
         0x20010db80000000002005efffe0053e3  IPv6 Address

               Address Set Three
         0x20010db80000000002005efffe0053d3  IPv6 Address

   As an alternative to the compact "well-known value" Template encoding
   used in the example above, the less compact explicit AFN encoding
   could have been used.  In that case, the IA APPsub-TLV would have
   started as follows:

         0x0002(10)    Type: Interface Addresses
         0x003C        Length: 60 (= 0x3C)
         0x0027        Address Sets End: 39 (= 0x27)
         0x4321        RBridge Nickname from which reachable
         0b10000000    Flags: Push Directory data
         0xD3          Confidence = 211
         0x3           Template: 3 AFNs
         0x4005        AFN: 48-bit MAC
         0x0001        AFN: IPv4
         0x400B        AFN: RBridge Port ID

   As a final point, since the 48-bit MAC addresses in these three
   Address Sets all have the same OUI (the IANA OUI [RFC7042]), it would
   have been possible to just have a MAC/24 value giving the lower
   24 bits of the MAC in each Address Set.  The OUI would then be
   supplied by a second Fixed Address sub-sub-TLV providing the OUI.
   With N Address Sets, this would have saved 3*N or 9 bytes, at a cost
   of 9 bytes (2 each for the Type and Length of the sub-sub-TLV, 2 for
   the OUI AFN, and 3 for the OUI).  So, with just three Address Sets,
   there would be no net savings; however, with a larger number of
   Address Sets, there would be a net savings.

Top      ToC       Page 24 
Acknowledgments

   The authors gratefully acknowledge the contributions and review by
   the following:

      Linda Dunbar, Sue Hares, Paul Kyzivat, Danny McPherson, and
      Gayle Noble

Authors' Addresses

   Donald Eastlake 3rd
   Huawei Technologies
   155 Beaver Street
   Milford, MA  01757
   United States of America

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


   Yizhou Li
   Huawei Technologies
   101 Software Avenue
   Nanjing  210012
   China

   Phone: +86-25-56622310
   Email: liyizhou@huawei.com