path: root/doc/rfc/rfc8171.txt

Internet Engineering Task Force (IETF)                   D. Eastlake 3rd
Request for Comments: 8171                                     L. Dunbar
Category: Standards Track                                         Huawei
ISSN: 2070-1721                                               R. Perlman
                                                                     EMC
                                                                   Y. Li
                                                                  Huawei
                                                               June 2017


         Transparent Interconnection of Lots of Links (TRILL):
                  Edge Directory Assistance Mechanisms

Abstract

   This document describes mechanisms for providing directory service to
   TRILL (Transparent Interconnection of Lots of Links) edge switches.
   The directory information provided can be used in reducing multi-
   destination traffic, particularly ARP / Neighbor Discovery (ND) and
   unknown unicast flooding.  It can also be used to detect traffic with
   forged source 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/rfc8171.
















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Copyright Notice

   Copyright (c) 2017 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. Uses of Directory Information ..............................5
      1.2. Terminology ................................................6
   2. Push Model Directory Assistance Mechanisms ......................7
      2.1. Requesting Push Service ....................................7
      2.2. Push Directory Servers .....................................8
      2.3. Push Directory Server State Machine ........................9
           2.3.1. Push Directory States ...............................9
           2.3.2. Push Directory Events and Conditions ...............11
           2.3.3. State Transition Diagram and Table .................13
      2.4. End Stations and Push Directories .........................15
      2.5. Additional Push Details ...................................15
      2.6. Providing Secondary Servers with Data from a
           Primary Server ............................................16
      2.7. Push Directory Configuration ..............................17
   3. Pull Model Directory Assistance Mechanisms .....................17
      3.1. Pull Directory Message: Common Format .....................19
           3.1.1. Version Negotiation ................................20
      3.2. Pull Directory Query and Response Messages ................21
           3.2.1. Pull Directory Query Message Format ................21
           3.2.2. Pull Directory Responses ...........................24
                  3.2.2.1. Pull Directory Response Message Format ....24
                  3.2.2.2. Pull Directory Forwarding .................27
      3.3. Cache Consistency .........................................28
           3.3.1. Update Message Format ..............................32
           3.3.2. Acknowledge Message Format .........................33
      3.4. Summary of Record Formats in Messages .....................34







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      3.5. End Stations and Pull Directories .........................34
           3.5.1. Pull Directory Hosted on an End Station ............35
           3.5.2. Use of Pull Directory by End Stations ..............36
           3.5.3. Native Pull Directory Messages .....................37
      3.6. Pull Directory Message Errors .............................38
           3.6.1. Error Codes ........................................39
           3.6.2. Sub-errors under Error Codes 1 and 3 ...............39
           3.6.3. Sub-errors under Error Codes 128 and 131 ...........40
      3.7. Additional Pull Details ...................................40
      3.8. The "No Data" Flag ........................................40
      3.9. Pull Directory Service Configuration ......................42
   4. Directory Use Strategies and Push-Pull Hybrids .................42
   5. TRILL ES-IS ....................................................44
      5.1. PDUs and System IDs .......................................45
      5.2. Adjacency, DRB Election, Port IDs, Hellos, and TLVs .......46
      5.3. Link State ................................................47
   6. Security Considerations ........................................47
      6.1. Directory Information Security ............................47
      6.2. Directory Confidentiality and Privacy .....................47
      6.3. Directory Message Security Considerations .................48
   7. IANA Considerations ............................................48
      7.1. ESADI-Parameter Data Extensions ...........................48
      7.2. RBridge Channel Protocol Numbers ..........................49
      7.3. The Pull Directory (PUL) and No Data (NOD) Bits ...........49
      7.4. TRILL Pull Directory QTYPEs ...............................50
      7.5. Pull Directory Error Code Registries ......................50
      7.6. TRILL-ES-IS MAC Address ...................................51
   8. References .....................................................51
      8.1. Normative References ......................................51
      8.2. Informative References ....................................54
   Acknowledgments ...................................................55
   Authors' Addresses ................................................55



















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1.  Introduction

   [RFC7067] gives a problem statement and high-level design for using
   directory servers to assist TRILL [RFC6325] [RFC7780] edge nodes in
   reducing multi-destination ARP / Neighbor Discovery (ND) [ARPND],
   reducing unknown unicast flooding traffic, and improving security
   against address spoofing within a TRILL campus.  Because
   multi-destination traffic becomes an increasing burden as a network
   scales up in number of nodes, reducing ARP/ND and unknown unicast
   flooding improves TRILL network scalability.  This document describes
   specific mechanisms for TRILL directory servers.

   The information held by the directory or directories is address
   mapping and reachability information -- most commonly, what MAC
   (Media Access Control) address [RFC7042] corresponds to an IP address
   within a Data Label (VLAN or FGL (Fine-Grained Label) [RFC7172]) and
   the egress TRILL switch (RBridge), and, optionally, what specific
   port on that TRILL switch, from which that MAC address is reachable.
   But it could be what IP address corresponds to a MAC address or
   possibly other address mapping or reachability information.

   The mechanism used to initially populate directory data in primary
   servers is beyond the scope of this document.  A primary server can
   use the Push Directory service to provide directory data to secondary
   servers, as described in Section 2.6.  In the data-center
   environment, it is common for orchestration software to know and
   control where all the IP addresses, MAC addresses, and VLANs/tenants
   are in a data center.  Thus, such orchestration software can be
   appropriate for providing the directory function or for supplying the
   directory or directories with directory information.

   Efficient routing of unicast traffic in a TRILL campus assumes that
   the mapping of destination MAC addresses to edge RBridges is stable
   enough that the default data-plane learning of TRILL and/or the use
   of directories reduces to an acceptable level the need to flood
   packets where the location of the destination is unknown.  Although
   not prohibited, "ephemeral" MAC addresses are unlikely to be used in
   such an environment.  Directories need not be complete, and in the
   case that any ephemeral MAC addresses were in use, they would
   probably not be included in directory information.

   Directory services can be offered in a Push Mode, Pull Mode, or both
   [RFC7067] at the discretion of the server.  Push Mode, in which a
   directory server pushes information to TRILL switches indicating
   interest, is specified in Section 2.  Pull Mode, in which a TRILL
   switch queries a server for the information it wants, is specified in
   Section 3.  More detail on modes of operation, including hybrid
   Push/Pull, are provided in Section 4.



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1.1.  Uses of Directory Information

   A TRILL switch can consult directory information whenever it wants by
   (1) searching through information that has been retained after being
   pushed to it or pulled by it or (2) requesting information from a
   Pull Directory.  However, the following are expected to be the most
   common circumstances leading to the use of directory information.
   All of these are cases of ingressing (or originating) a native frame.

   1. ARP requests and replies [RFC826] are normally broadcast.  But a
      directory-assisted edge TRILL switch could intercept ARP messages
      and reply if the TRILL switch has the relevant information
      [ARPND].

   2. IPv6 ND [RFC4861] requests and replies are normally multicast.
      Except in the case of Secure Neighbor Discovery (SEND) [RFC3971],
      where possession of the right keying material might be required, a
      directory-assisted edge TRILL switch could intercept ND messages
      and reply if the TRILL switch has the relevant information
      [ARPND].

   3. Unknown destination MAC addresses normally cause a native frame to
      be flooded.  An edge TRILL switch ingressing a native frame
      necessarily has to determine if it knows the egress RBridge from
      which the destination MAC address of the frame (in the frame's
      VLAN or FGL) is reachable.  It might have learned that information
      from the directory or could query the directory if it does not
      know it.  Furthermore, if the edge TRILL switch has complete
      directory information, it can detect a forged source MAC or IP
      address in any native frame and discard the frame if it finds such
      a forged address.

   4. RARP [RFC903] (Reverse ARP) is similar to ARP (item 1 above).


















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1.2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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

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

   CSNP Time: Complete Sequence Number Protocol Data Unit (PDU) time.
      See ESADI [RFC7357] and Section 7.1 below.

   Data Label: VLAN or FGL.

   ESADI: End Station Address Distribution Information [RFC7357].

   FGL: Fine-Grained Label [RFC7172].

   FR: Flood Record flag bit.  See Section 3.2.1.

   Host: A physical server or a virtual machine.  A host must have a MAC
      address and usually has at least one IP address.

   Interested Labels sub-TLV: Short for "Interested Labels and Spanning
      Tree Roots sub-TLV" [RFC7176].

   Interested VLANs sub-TLV: Short for "Interested VLANs and Spanning
      Tree Roots sub-TLV" [RFC7176].

   IP: Internet Protocol.  In this document, IP includes both IPv4
      and IPv6.

   MAC address: Media Access Control address [RFC7042].

   MacDA: Destination MAC address.

   MacSA: Source MAC address.

   OV: Overflow flag bit.  See Section 3.2.2.1.

   PDSS: Push Directory Server Status.  See Sections 2 and 7.1.





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   Primary server: A directory server that obtains the information it is
      providing by a reliable mechanism designed to assure the freshness
      of that information.  This mechanism is outside the scope of this
      document.  (See "Secondary server" below.)

   PUL: Pull Directory flag bit.  See Sections 3 and 7.3.

   RBridge: An alternative name for a TRILL switch.

   Secondary server: A directory server that obtains the information it
      is providing from one or more primary servers.

   TLV: Type, Length, Value.

   TRILL: Transparent Interconnection of Lots of Links or Tunneled
      Routing in the Link Layer.

   TRILL switch: A device that implements the TRILL protocol.

2.  Push Model Directory Assistance Mechanisms

   In the Push Model [RFC7067], one or more Push Directory servers
   reside at TRILL switches and "push down" the address mapping
   information for the various addresses associated with end-station
   interfaces and the TRILL switches from which those interfaces are
   reachable [RFC7961].  This service is scoped by Data Label (VLAN or
   FGL [RFC7172]).  A Push Directory advertises when, for a Data Label,
   it is configured to be a directory having complete information and
   also has actually pushed all the information it has.  It might be
   pushing only a subset of the mapping and/or reachability information
   for a Data Label.  The Push Model uses the ESADI [RFC7357] protocol
   as its distribution mechanism.

   With the Push Model, if complete address mapping information for a
   Data Label is being pushed, a TRILL switch (RBridge) that has that
   complete information and is ingressing a native frame can simply drop
   the frame if the destination unicast MAC address can't be found in
   the mapping information available, instead of flooding the frame
   (ingressing it as an unknown MAC destination TRILL Data frame).  But
   this will result in lost traffic if the ingress TRILL switch's
   directory information is incomplete.

2.1.  Requesting Push Service

   In the Push Model, it is necessary to have a way for a TRILL switch
   to subscribe to information from the directory server(s).  TRILL
   switches simply use the ESADI [RFC7357] protocol mechanism to
   announce, in their core IS-IS Link State PDUs (LSPs), the Data Labels



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   for which they are participating in ESADI by using the Interested
   VLANs sub-TLV [RFC7176] and/or the Interested Labels sub-TLV
   [RFC7176].  This will cause the directory information to be pushed to
   them for all such Data Labels that are being served by the one or
   more Push Directory servers.

2.2.  Push Directory Servers

   Push Directory servers advertise, through ESADI, their availability
   to push the mapping information for a particular Data Label by
   setting the PDSS in their ESADI-Parameter APPsub-TLV for that ESADI
   instance (see [RFC7357] and Section 7.1) to a non-zero value.  This
   PDSS field setting is visible to other ESADI participants, including
   other Push Directory servers, for that Data Label.  Each Push
   Directory server MUST participate in ESADI for the Data Labels for
   which it will push mappings and set the PDSS field in its
   ESADI-Parameter APPsub-TLV for that Data Label.  For increased
   robustness, increased bandwidth capability, and improved locality, it
   is useful to have multiple Push Directory servers for each
   Data Label.  Each Push Directory server is configured with a
   number N, which is in the range 1 through 8 and defaults to 2, for
   each Data Label for which it can push directory information (see
   "PushDirServers" in Section 2.7).  If the Push Directory servers for
   a Data Label are configured consistently with the same N and at least
   N servers are available, then N copies of that directory will be
   pushed.

   Each Push Directory server also has a configurable 8-bit priority
   (PushDirPriority) to be Active, which defaults to 0x3F (see
   Section 2.7).  This priority is treated as an unsigned integer, where
   the larger magnitude means higher priority.  This priority appears in
   its ESADI-Parameter APPsub-TLV (see Section 7.1).  In the case of a
   tie in this configurable priority, the System ID of the TRILL switch
   acting as the server is used as a tiebreaker and is treated as an
   unsigned 6-byte integer, where the larger magnitude indicates higher
   priority.

   For each Data Label it can serve, each Push Directory server checks
   to see if there appear to be enough higher-priority servers to push
   the desired number of copies.  It does this by ordering, by priority,
   the Push Directory servers whose advertisements are present in the
   ESADI link-state database for that Data Label and that are
   data reachable [RFC7780] as indicated by its IS-IS link-state
   database.  The Push Directory server then determines its own position
   in that order.  If a Push Directory server's configuration indicates
   that N copies of the mappings for a Data Label should be pushed and
   the server finds that it is number K in the priority ordering (where
   number 1 in the ordered list is highest priority and the last is



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   lowest priority), then if K is less than or equal to N, the Push
   Directory server is Active.  If K is greater than N, it is Stand-By.
   Active and Stand-By behavior are specified below in Section 2.3.

   For a Push Directory to reside on an end station, one or more TRILL
   switches locally connected to that end station must proxy for the
   Push Directory server and advertise themselves in ESADI as Push
   Directory servers.  It appears to the rest of the TRILL campus that
   these TRILL switches (that are proxying for the end station) are the
   Push Directory server(s).  The protocol between such a Push Directory
   end station and the one or more proxying TRILL switches acting as
   Push Directory servers is beyond the scope of this document.

2.3.  Push Directory Server State Machine

   The subsections below describe the states, events, and corresponding
   actions for Push Directory servers.

   The meanings of possible values of the PDSS field in a Push
   Directory's ESADI-Parameter APPsub-TLV are summarized in the table
   below.

       PDSS         Meaning
       ----   ------------------------------------------------------
         0     Not a Push Directory server
         1     Push Directory server in Stand-By Mode
         2     Push Directory server in Active Mode but not complete
         3     Push Directory server in Active Mode that has pushed
               complete data

2.3.1.  Push Directory States

   A Push Directory server is in one of seven states, as listed below,
   for each Data Label it can serve.  The name of each state is followed
   by a symbol that starts and ends with an angle bracket (for example,
   "<S1>") and represents the state.  The value that the Push Directory
   server advertises in the PDSS is determined by the state.  In
   addition, it has an internal State-Transition-Time variable for each
   Data Label it serves that is set at each state transition and that
   enables it to determine how long it has been in its current state for
   that Data Label.










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   Down <S1>: A completely shut down virtual state, defined for
      convenience in specifying state diagrams.  A Push Directory server
      in this state does not advertise any Push Directory data.  It may
      be participating in ESADI [RFC7357] with the PDSS field set to 0
      in its ESADI-Parameter APPsub-TLV, or it might not be
      participating in ESADI at all.  All states other than the Down
      state are considered to be Up states and imply a non-zero
      PDSS field.

   Stand-By <S2>: No Push Directory data is advertised.  Any outstanding
      ESADI-LSP fragments containing directory data are updated to
      remove that data, and if the result is an empty fragment (contains
      nothing except possibly an Authentication TLV), the fragment is
      purged.  The Push Directory participates in ESADI [RFC7357] and
      advertises its ESADI fragment zero that includes an
      ESADI-Parameter APPsub-TLV with the PDSS field set to 1.

   Active <S3>: The Push Directory participates in ESADI [RFC7357] and
      advertises its ESADI fragment zero that includes an
      ESADI-Parameter APPsub-TLV with the PDSS field set to 2.  It also
      advertises its directory data and any changes through ESADI
      [RFC7357] in its ESADI-LSPs, using the Interface Addresses
      APPsub-TLV [RFC7961], and updates that information as it changes.

   Active Completing <S4>: The same behavior as the Active state, except
      that the server responds differently to events.  The purpose of
      this state is to be sure that there has been enough time for
      directory information to propagate to subscribing edge TRILL
      switches (see "Time Condition", as defined in Section 2.3.2)
      before the directory server advertises that the information is
      complete.

   Active Complete <S5>: The same behavior as Active, except that the
      PDSS field in the ESADI-Parameter APPsub-TLV is set to 3 and the
      server responds differently to events.

   Going Stand-By Was Complete <S6>: The same behavior as Active, except
      that the server responds differently to events.  The purpose of
      this state is to be sure that the information indicating that the
      directory will no longer be complete has enough time to propagate
      to edge TRILL switches (see "Time Condition" in Section 2.3.2)
      before the directory server stops advertising updates to the
      information.  (See note below.)

   Active Uncompleting <S7>: The same behavior as Active, except that it
      responds differently to events.  The purpose of this state is to
      be sure that the information indicating that the directory will no
      longer be complete has enough time to propagate to edge TRILL



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      switches (see "Time Condition" in Section 2.3.2) before the
      directory server might stop advertising updates to the
      information.  (See note below.)

      Note: It might appear that a Push Directory could transition
      directly from Active Complete to Active, since the Active state
      continues to advertise updates, eliminating the need for the
      Active Uncompleting transition state.  But consider the case of
      the Push Directory that was complete being configured to be
      incomplete and then the Stand-By Condition (see Section 2.3.2)
      occurring shortly thereafter.  If the first of these two events
      caused the server to transition directly to the Active state,
      then later, when the Stand-By Condition occurred, it would
      immediately transition to Stand-By and stop advertising updates
      even though there might not have been enough time for knowledge of
      its incompleteness to have propagated to all edge TRILL switches.

   The following table lists each state and its corresponding PDSS
   value:

       State                                 PDSS
      --------------------------------      ------
      Down <S1>                               0
      Stand-By <S2>                           1
      Active <S3>                             2
      Active Completing <S4>                  2
      Active Complete <S5>                    3
      Going Stand-By Was Complete <S6>        2
      Active Uncompleting <S7>                2

2.3.2.  Push Directory Events and Conditions

   Three auxiliary conditions, referenced later in this subsection, are
   defined as follows:

   The Activate Condition: In order to have the desired number of Push
      Directory servers pushing data for Data Label X, this Push
      Directory server should be active.  This is determined by the
      server finding that (a) it is priority K among the data-reachable
      Push Directory servers (where the highest-priority server is 1)
      for Data Label X, (b) it is configured that there should be
      N copies pushed for Data Label X, and (c) K is less than or equal
      to N.  For example, the Push Directory server is configured so
      that two copies should be pushed and finds that it is priority 1
      or 2 among the Push Directory servers that are visible in its
      ESADI link-state database and that are data reachable, as
      indicated by its IS-IS link-state database.




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   The Stand-By Condition: In order to have the desired number of Push
      Directory servers pushing data for Data Label X, this Push
      Directory server should be Stand-By (not Active).  This is
      determined by the server finding that (a) it is priority K among
      the data-reachable Push Directory servers (where the
      highest-priority server is 1) for Data Label X, (b) it is
      configured that there should be N copies pushed for Data Label X,
      and (c) K is greater than N.  For example, the Push Directory
      server is configured so that two copies should be pushed and finds
      that it is priority 3 or lower priority (higher number) among the
      available Push Directory servers.

   The Time Condition: The Push Directory server has been in its current
      state for a configurable amount of time (PushDirTimer) that
      defaults to twice its CSNP (Complete Sequence Number PDU) time
      (see Sections 2.7 and 7.1).

   The events and conditions listed below cause state transitions in
   Push Directory servers.

   1. The Push Directory server comes up.

   2. The Push Directory server or the TRILL switch on which it resides
      is being shut down.  This is a persistent condition, unless the
      shutdown is canceled.  So, for example, a Push Directory server in
      the Going Stand-By Was Complete state does not transition out of
      that state due to this condition but, after (1) the Time Condition
      is met and (2) the directory transitions to Stand-By and then
      performs the actions required there (such as purging LSPs),
      continues to the Down state if this condition is still true.
      Similar comments apply to events/conditions 3, 4, and 5.

   3. The Activate Condition is met, and the server's configuration
      indicates that it does not have complete data.

   4. The Stand-By Condition is met.

   5. The Activate Condition is met, and the server's configuration
      indicates that it has complete data.

   6. The server's configuration is changed to indicate that it does not
      have complete data.

   7. The Time Condition is met.







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2.3.3.  State Transition Diagram and Table

   The state transition table is as follows:

     |    |        |      |  Active  | Active |   Going    |   Active
State|Down|Stand-By|Active|Completing|Complete|  Stand-By  |Uncompleting
-----+    |        |      |          |        |Was Complete|
Event|<S1>|  <S2>  | <S3> |   <S4>   |  <S5>  |    <S6>    |    <S7>
-----+----+--------+------+----------+--------+------------+------------
  1  |<S2>|  N/A   | N/A  |   N/A    |  N/A   |  N/A       |    N/A
  2  |<S1>|  <S1>  | <S2> |   <S2>   |  <S6>  |  <S6>      |    <S7>
  3  |<S1>|  <S3>  | <S3> |   <S3>   |  <S7>  |  <S3>      |    <S7>
  4  |<S1>|  <S2>  | <S2> |   <S2>   |  <S6>  |  <S6>      |    <S6>
  5  |<S1>|  <S4>  | <S4> |   <S4>   |  <S5>  |  <S5>      |    <S5>
  6  |<S1>|  <S2>  | <S3> |   <S3>   |  <S7>  |  <S6>      |    <S7>
  7  |<S1>|  <S2>  | <S3> |   <S5>   |  <S5>  |  <S2>      |    <S3>



































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   The above state table is equivalent to the following transition
   diagram:

      +-----------+
      | Down <S1> |<---------+
      +-----------+          |
        |1  ^   | 3,4,5,6,7  |
        |   |   +------------+
        V   |2
      +---------------+
      | Stand-By <S2> |<--------------------------------------+
      +---------------+    ^   ^            ^                 |
        |5   |3  |1,4,6,7  |   |            |                 |
        |    |   +---------+   |            |                 |
        |    V                 |2,4         |                 |
        |  +---------------------+          |                 |
        |  | Active <S3>         |<---------|-------------+   |
        |  +---------------------+     ^    |             |   |
        |   |5  ^    |1,3,6,7  ^       |    |             |   |
        |   |   |    |         |       |    |             |   |
        |   |   |    +---------+       |    |             |   |
        |   |   |                      |    |             |   |
        V   V   |3,6                   |    |             |   |
      +------------------------+       |    |             |   |
      | Active Completing <S4> |------------+             |   |
      +------------------------+ 2,4   |                  |   |
        |7  |1,5    ^                  |                  |   |
        |   |       |                  |                  |   |
        |   +-------+                  |                  |   |
        |                              |                  |   |
        |        +------------------------------------+   |   |
        |        |                     |              |   |   |
        V        V                     |7             |5  |3  |7
      +-------------+ 3,6    +----------------+ 4  +----------------+
      |    Active   |------->|     Active     |--->| Going Stand-By |
      |   Complete  |        |  Uncompleting  |    |  Was Complete  |
      |     <S5>    |<-------|      <S7>      |    |      <S6>      |
      +-------------+      5 +----------------+    +----------------+
       |1,5,7  ^  |2,4         |1,2,3,6     ^        ^   |1,2,4,6 ^
       |       |  |            |            |        |   |        |
       +-------+  |            +------------+        |   +--------+
                  |                                  |
                  +----------------------------------+

                    Figure 1: Push Server State Diagram






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2.4.  End Stations and Push Directories

   End-station hosting and end-station use of Push Directories are
   outside the scope of this document.  Push Directory information
   distribution is accomplished using ESADI [RFC7357], which does not
   operate to end stations.  In the future, ESADI might be extended to
   operate to end stations, or some other method, such as BGP, might be
   specified as a way to support end-station hosting or end-station use
   of Push Directories.

2.5.  Additional Push Details

   Push Directory mappings can be distinguished from other data
   distributed through ESADI, because mappings are distributed only with
   the Interface Addresses APPsub-TLV [RFC7961] and are flagged in that
   APPsub-TLV as being Push Directory data.

   TRILL switches, whether or not they are Push Directory servers, MAY
   continue to advertise any locally learned MAC attachment information
   in ESADI [RFC7357] using the MAC-Reachability TLV [RFC6165].
   However, if a Data Label is being served by complete Push Directory
   servers, advertising such a locally learned MAC attachment generally
   SHOULD NOT be done, as it would not add anything and would just waste
   bandwidth and ESADI link-state space.  An exception might be when a
   TRILL switch learns local MAC connectivity and that information
   appears to be missing from the directory mapping.

   Because a Push Directory server needs to advertise interest in one or
   more Data Labels even though it might not want to receive
   multi-destination TRILL Data packets in those Data Labels, the
   "No Data" (NOD) flag bit is provided, as discussed in Section 3.8.

   When a Push Directory server is no longer data reachable [RFC7780],
   as indicated by the IS-IS link-state database, other TRILL switches
   MUST ignore any Push Directory data from that server, because it is
   no longer being updated and may be stale.

   The nature of dynamic distributed asynchronous systems is such that
   it is impossible for a TRILL switch receiving Push Directory
   information to be absolutely certain that it has complete
   information.  However, it can obtain a reasonable assurance of
   complete information by requiring that two conditions be met:

   1. The PDSS field is 3 in the ESADI fragment zero from the server for
      the relevant Data Label.






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   2. As far as it can tell, it has had continuous data connectivity to
      the server for a configurable amount of time that defaults to
      twice the server's CSNP time (see "PushDirTimer" in Section 2.7).

   Condition 2 is necessary because a client TRILL switch might be just
   coming up and receive an ESADI-LSP meeting the requirement in
   condition 1 above but has not yet received all of the ESADI-LSP
   fragments from the Push Directory server.

   Likewise, due to various delays, when an end station connects to or
   disconnects from the campus, there are timing differences between
   such a connection or disconnection, the update of directory
   information at the directory, and the update of directory information
   at any particular RBridge in the TRILL campus.  Thus, there is
   commonly a small window during which an RBridge using directory
   information might either (1) drop or unnecessarily flood a frame as
   having an unknown unicast destination or (2) encapsulate a frame to
   an edge RBridge where the end station is no longer connected when the
   frame arrives at that edge RBridge.

   There may be conflicts between mapping information from different
   Push Directory servers or conflicts between locally learned
   information and information received from a Push Directory server.
   In cases of such conflicts, information with a higher confidence
   value [RFC6325] [RFC7961] is preferred over information with a lower
   confidence value.  In cases of equal confidence values, Push
   Directory information is preferred to locally learned information,
   and if information from Push Directory servers conflicts, the
   information from the higher-priority Push Directory server is
   preferred.

2.6.  Providing Secondary Servers with Data from a Primary Server

   A secondary Push or Pull Directory server is one that obtains its
   data from a primary directory server.  Such systems, where some
   directory servers can be populated from others, have been found
   useful for multiple-server directory applications -- for example, in
   the DNS, where it is the normal case that some authoritative servers
   (secondary servers) are populated with data from other authoritative
   servers (primary servers).

   Other techniques MAY be used, but by default, this data transfer
   occurs through the primary server acting as a Push Directory server
   for the Data Labels involved, while the secondary directory server
   takes the pushed data it receives from the highest-priority Push
   Directory server and re-originates it.  Such a secondary server
   may be a Push Directory server, a Pull Directory server, or both for
   any particular Data Label.  Because the data from a secondary server



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   will necessarily be at least a little less fresh than that from a
   primary server, it is RECOMMENDED that the re-originated secondary
   server's data be given a confidence level at least one less than that
   of the data as received from the primary server (or unchanged if it
   is already of minimum confidence).

2.7.  Push Directory Configuration

   The following configuration parameters, per Data Label, are available
   for controlling Push Directory behavior:

            Name          Range/Setting     Default       Section
      ---------------     -------------    ---------    ------------
      PushDirService         true/false        false    2.2
      PushDirServers                1-8            2    2.2
      PushDirPriority             0-255         0x3F    2.2
      PushDirComplete        true/false        false    2.3.1, 2.3.2
      PushDirTimer                1-511     2 * CSNP    2.3.2, 2.5

   PushDirService is a boolean.  When false, Push Directory service is
   not provided; when true, it is.

   PushDirComplete is a boolean.  When false, the server never indicates
   that the information it has pushed is complete; when true, it does so
   indicate after pushing all the information it knows.

   PushDirTimer defaults to two times the ESADI-CSNP configuration value
   but not less than 1 second.

3.  Pull Model Directory Assistance Mechanisms

   In the Pull Model [RFC7067], a TRILL switch (RBridge) pulls directory
   information from an appropriate directory server when needed.

   A TRILL switch that makes use of Pull Directory services must
   implement appropriate connections between its directory utilization
   and its link-state database and link-state updating.  For example,
   Pull Directory servers for a particular Data Label X are found by
   looking in the core TRILL IS-IS link-state database for
   data-reachable [RFC7780] TRILL switches that advertise themselves by
   setting the Pull Directory flag (PUL) to 1 in their Interested VLANs
   sub-TLV or Interested Labels sub-TLV (see Section 7.3) for that Data
   Label.  The set of such switches can change with configuration
   changes by network management, such as the following:

   o  the startup or shutdown of Pull Directory servers





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   o  changes in network topology, such as the connection or
      disconnection of TRILL switches that are Pull Directory servers

   o  network partition or merger

   As described in Section 3.7, a TRILL switch MUST be able to detect
   that a Pull Directory from which it has cached data is no longer
   data reachable so that it can discard such cached data.

   If multiple data-reachable TRILL switches indicate in the link-state
   database that they are Pull Directory servers for a particular Data
   Label, pull requests can be sent to any one or more of them, but it
   is RECOMMENDED that pull requests be preferentially sent to the
   server or servers that are lowest cost from the requesting TRILL
   switch.

   Pull Directory requests are sent by encapsulating them in an RBridge
   Channel [RFC7178] message using the Pull Directory channel protocol
   number (see Section 7.2).  Responses are returned in an RBridge
   Channel message using the same channel protocol number.  See
   Section 3.2 for Query and Response Message formats.  For cache
   consistency or notification purposes, Pull Directory servers, under
   certain conditions, MUST send unsolicited Update Messages to client
   TRILL switches they believe may be holding old data.  Those clients
   can acknowledge such updates, as described in Section 3.3.  All these
   messages have a common header, as described in Section 3.1.  Errors
   are returned as described in Section 3.6.

   The requests to Pull Directory servers are typically derived from
   ingressed ARP [RFC826], ND [RFC4861], RARP [RFC903], or SEND
   [RFC3971] messages, or data frames with unknown unicast destination
   MAC addresses, intercepted by an ingress TRILL switch, as described
   in Section 1.1.

   Pull Directory responses include an amount of time for which the
   response should be considered valid.  This includes negative
   responses that indicate that no data is available.  It is RECOMMENDED
   that both positive responses with data and negative responses be
   cached and used to locally handle ARP, ND, RARP, unknown destination
   MAC frames, or the like [ARPND], until the responses expire.  If
   information previously pulled is about to expire, a TRILL switch MAY
   try to refresh it by issuing a new pull request but, to avoid
   unnecessary requests, SHOULD NOT do so unless it has been recently
   used.  The validity timer of cached Pull Directory responses is NOT
   reset or extended merely because that cache entry is used.






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3.1.  Pull Directory Message: Common Format

   All Pull Directory messages are transmitted as the Channel
   Protocol-specific payload of RBridge Channel messages [RFC7178].
   Pull Directory messages are formatted as described herein, starting
   with the following common 8-byte header:

                           1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Ver  | Type  | Flags | Count |      Err      |    SubErr     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence Number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type Specific Payload - variable length
      +-+-+- ...

      Ver: Version of the Pull Directory protocol.  An unsigned integer.
         Version 0 (zero) is specified in this document.  See
         Section 3.1.1 for a discussion of version negotiation.

      Type: The Pull Directory message type, as follows:

                  Type   Section    Name
                  ----   -------   ------------
                     0    -         Reserved
                     1    3.2.1     Query
                     2    3.2.2     Response
                     3    3.3.1     Update
                     4    3.3.2     Acknowledge
                  5-14    -         Unassigned
                    15    -         Reserved

      Flags: Four flag bits whose meaning depends on the Pull Directory
         message type.  Flags whose meanings are not specified are
         reserved, MUST be sent as zero, and MUST be ignored on receipt.

      Count: Some Pull Directory message types specified herein have
         zero or more occurrences of a Record as part of the
         type-specific payload.  The Count field is the number of
         occurrences of that Record and is expressed as an unsigned
         integer.  For any Pull Directory messages not structured with
         such occurrences, this field MUST be sent as zero and ignored
         on receipt.







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      Err, SubErr: A two-part error code.  These fields are only used in
         Reply Messages.  In messages that are requests or updates,
         these fields MUST be sent as zero and ignored on receipt.  An
         Err field containing the value zero means no error.  The
         meaning of values in the SubErr field depends on the value of
         the Err field, but in all cases, a zero SubErr field is allowed
         and provides no additional information beyond the value of the
         Err field.

      Sequence Number: An identifying 32-bit quantity set by the TRILL
         switch sending a request or other unsolicited message and
         returned in every corresponding reply or acknowledgment.  It is
         used to match up responses with the message to which they
         respond.

      Type Specific Payload: Format depends on the Pull Directory
         message type.

3.1.1.  Version Negotiation

   The version number (Ver) in the Pull Directory message header is
   incremented for a future version with changes such that TRILL
   directory messages cannot be parsed correctly by an earlier version.
   Ver is not incremented for minor changes such as defining a new field
   value for an existing field.

   Pull Directory messages come in pairs (Request-Response,
   Update-Acknowledgment).  The version number in the Request/Update
   (Ver1) indicates the format of that message and the format of the
   corresponding returned Response/Acknowledgment.  The version number
   in the returned Response/Acknowledgment (Ver2) indicates the highest
   version number that the sender of that Response/Acknowledgment
   understands.

   In the most common case -- a well-configured network -- Ver1 and Ver2
   will be equal.

   If Ver2 is less than Ver1, the returned Response/Acknowledgment will
   be an error message saying that the version is not understood.

   If Ver2 is greater than Ver1 and the responder understands Ver1, it
   responds normally in Ver1 format.  However, if the responder does not
   understand Ver1, it MUST send a "Version not understood" error
   message (Section 3.6.2) correctly formatted for Ver1.  Thus, all
   implementations that support some version X MUST be able to send a
   Version not understood error message correctly formatted for all
   lower versions down to version 0.




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3.2.  Pull Directory Query and Response Messages

   The formats of Pull Directory Query Messages and Pull Directory
   Response Messages are specified in Sections 3.2.1 and 3.2.2.1,
   respectively.

3.2.1.  Pull Directory Query Message Format

   A Pull Directory Query Message is sent as the Channel
   Protocol-specific content of an RBridge Channel message [RFC7178]
   TRILL Data packet or as a native RBridge Channel data frame (see
   Section 3.5).  The Data Label of the packet is the Data Label in
   which the query is being made.  The priority of the RBridge Channel
   message is a mapping of the priority of the ingressed frame that
   caused the query.  The default mapping depends, per Data Label, on
   the strategy (see Section 4) or a configured priority (see
   "DirGenQPriority" in Section 3.9) for generated queries.  (Generated
   queries are those queries that are not the result of a mapping -- for
   example, a query to refresh a cache entry.)  The Channel
   Protocol-specific data is formatted as a header and a sequence of
   zero or more QUERY Records as follows:

                           1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Ver  | Type  | Flags | Count |      Err      |    SubErr     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence Number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | QUERY 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | QUERY 2
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | QUERY K
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...

      Ver, Sequence Number: See Section 3.1.

      Type: 1 for Query.  Queries received by a TRILL switch that is not
         a Pull Directory for the relevant Data Label result in an error
         response (see Section 3.6) unless inhibited by rate limiting.
         (See [RFC7178] for information on the Response Message that is
         generated if the recipient implements the RBridge Channel
         features but does not implement the Pull Directory RBridge
         Channel Protocol.)




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      Flags, Err, and SubErr: MUST be sent as zero and ignored on
         receipt.

      Count: Count is the number of QUERY Records present.  A
         Query Message Count of 0 is explicitly allowed, for the purpose
         of pinging a Pull Directory server to see if it is responding.
         On receipt of such an empty Query Message, a Response Message
         that also has a Count of 0 is returned unless inhibited by rate
         limiting.

      QUERY: Each QUERY Record within a Pull Directory Query Message is
         formatted as follows:

                 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               |        SIZE           |FR|  RESV  |   QTYPE   |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             If QTYPE = 1
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               |                      AFN                      |
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               |  Query Address ...
               +--+--+--+--+--+--+--+--+--+--+--...
             If QTYPE = 2 or 5
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               |  Query Frame ...
               +--+--+--+--+--+--+--+--+--+--+--...

         SIZE: Size of the QUERY Record in bytes, expressed as an
            unsigned integer and not including the SIZE field and
            following byte.  A value of SIZE so large that the material
            doesn't fit in the Query Message indicates a malformed
            QUERY Record.  A QUERY Record with such an illegal SIZE
            value, and any subsequent QUERY Records, MUST be ignored,
            and the entire Query Message MAY be ignored.

         FR: The Flood Record flag.  Ignored if QTYPE is 1.  If QTYPE is
            2 or 5 and the directory information sought is not found,
            the frame provided is flooded; otherwise, it is not
            forwarded.  See Section 3.2.2.2.  For QTYPEs other than 2 or
            5, the FR flag has no effect.

         RESV: A block of three reserved bits.  MUST be sent as zero and
            ignored on receipt.







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         QTYPE: There are several types of QUERY Records currently
            defined in two classes, as follows: (1) a QUERY Record that
            provides an explicit address and asks for all addresses for
            the interface specified by the Query Address and (2) a
            QUERY Record that includes a frame.  The fields of each are
            specified below.  Values of QTYPE are as follows:

            QTYPE   Description
            -----   -------------------------------
               0    Reserved
               1    Address query
               2    Frame query
             3-4    Unassigned
               5    Unknown unicast MAC Query Frame
            6-14    Unassigned
              15    Reserved

         AFN: Address Family Number of the Query Address.

         Query Address: The query is asking for any other addresses, and
            the nickname of the TRILL switch from which they are
            reachable, that correspond to the same interface as this
            address, within the Data Label of the query of the address
            provided.  A typical Query Address would be something like
            the following:

            1. A 48-bit MAC address, with the querying TRILL switch
               primarily interested in either

               a. the RBridge by which that MAC address is reachable, so
                  that the querying RBridge can forward an unknown
                  (before the query) destination MAC address native
                  frame as a unicast TRILL Data packet rather than
                  flooding it, or

               b. the IP address corresponding to the MAC address, so
                  that the RBridge can locally respond to a RARP
                  [RFC903] native frame.

            2. An IPv4 or IPv6 address, with the querying RBridge
               interested in the corresponding MAC address so it can
               locally respond to an ARP [RFC826] or ND [RFC4861] native
               frame [ARPND].

            But the Query Address could be some other address type for
            which an AFN has been assigned, such as a 64-bit MAC address
            [RFC7042] or a CLNS (connectionless-mode network service)
            [X.233] address.



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         Query Frame: Where a QUERY Record is the result of an ARP, ND,
            RARP, SEND, or unknown unicast MAC destination address, the
            ingress TRILL switch MAY send the frame to a Pull Directory
            server if the frame is small enough that the resulting Query
            Message fits into a TRILL Data packet within the campus MTU.
            The full frame is included, starting with the destination
            and source MAC addresses, but does not include the Frame
            Check Sequence (FCS).

   If no response to a Pull Directory Query Message is received within a
   configurable timeout (see "DirQueryTimeout" in Section 3.9), then the
   Query Message should be retransmitted with the same Sequence Number
   (up to a configurable number of times (see "DirQueryRetries" in
   Section 3.9)).  If there are multiple QUERY Records in a
   Query Message, responses to various subsets of these QUERY Records
   can be received before the timeout.  In that case, the remaining
   unanswered QUERY Records should be resent in a new Query Message with
   a new Sequence Number.  If a TRILL switch is not capable of handling
   partial responses to queries with multiple QUERY Records, it MUST NOT
   send a Request Message with more than one QUERY Record in it.

   See Section 3.6 for a discussion of how Query Message errors are
   handled.

3.2.2.  Pull Directory Responses

   A Pull Directory Query Message results in a Pull Directory Response
   Message as described in Section 3.2.2.1.

   In addition, if the QUERY Record QTYPE was 2 or 5, the frame included
   in the Query may be modified and forwarded by the Pull Directory
   server as described in Section 3.2.2.2.

3.2.2.1.  Pull Directory Response Message Format

   Pull Directory Response Messages are sent as the
   Channel Protocol-specific content of an RBridge Channel message
   [RFC7178] TRILL Data packet or as a native RBridge Channel data frame
   (see Section 3.5).  Responses are sent with the same Data Label and
   priority as the Query Message to which they correspond, except that
   the Response Message priority is limited to be no more than the
   configured value DirRespMaxPriority (Section 3.9).









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   The RBridge Channel Protocol-specific data format is as follows:

                           1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Ver  | Type  | Flags | Count |      Err      |    SubErr     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence Number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | RESPONSE 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | RESPONSE 2
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | RESPONSE K
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...

      Ver, Sequence Number: As specified in Section 3.1.

      Type: 2 = Response.

      Flags: MUST be sent as zero and ignored on receipt.

      Count: Count is the number of RESPONSE Records present in the
         Response Message.

      Err, SubErr: A two-part error code.  Zero, unless there was an
         error in the Query Message (in which case, see Section 3.6).

      RESPONSE: Each RESPONSE Record within a Pull Directory Response
         Message is formatted as follows:

           0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
         +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
         |         SIZE          |OV|  RESV  |   Index   |
         +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
         |                   Lifetime                    |
         +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
         |                Response Data ...
         +--+--+--+--+--+--+--+--+--+--+--...

         SIZE: The size of the RESPONSE Record is an unsigned integer
            number of bytes, not including the SIZE field and following
            byte.  A value of SIZE so large that the material doesn't
            fit in the Query Message indicates a malformed





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            RESPONSE Record.  A RESPONSE Record with such an excessive
            SIZE value, and any subsequent RESPONSE Records, MUST be
            ignored, and the entire Response Message MAY be ignored.

         OV: The overflow flag.  Indicates, as described below, that
            there was too much Response Data to include in one Response
            Message.

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

         Index: The relative index of the QUERY Record in the Query
            Message to which this RESPONSE Record corresponds.  The
            Index will always be 1 for Query Messages containing a
            single QUERY Record.  If the Index is larger than the Count
            was in the corresponding Query, that RESPONSE Record MUST be
            ignored, and subsequent RESPONSE Records or the entire
            Response Message MAY be ignored.

         Lifetime: The length of time, in units of 100 milliseconds,
            for which the response should be considered valid, except
            that the values zero and 2**16 - 1 are special.  If zero,
            the response can only be used for the particular query from
            which it resulted and MUST NOT be cached.  If 2**16 - 1, the
            response MAY be kept indefinitely but not after the Pull
            Directory server goes down or becomes unreachable.  (The
            maximum definite time that can be expressed is a little over
            1.8 hours.)

         Response Data: There are three types of RESPONSE Records:

         -  If the Err field of the encapsulating Response Message has a
            message-level error code in it, then the RESPONSE Records
            are omitted and Count will be 0.  See Section 3.6 for
            additional information on errors.

         -  If the Err field of the encapsulating Response Message has a
            record-level error code in it, then the RESPONSE Records are
            those having that error, as further described in
            Section 3.6.

         -  If the Err field of the encapsulating Response Message is 0,
            then the Response Data in each RESPONSE Record is formatted
            as the value part of an Interface Addresses APPsub-TLV
            [RFC7961].  The maximum size of such contents is 255 bytes,
            in which case the RESPONSE Record SIZE field is 255.





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   Multiple RESPONSE Records can appear in a Response Message with the
   same Index if an answer to the QUERY Record consists of multiple
   Interface Addresses APPsub-TLV values.  This would be necessary if,
   for example, a MAC address within a Data Label appears to be
   reachable by multiple TRILL switches.  However, all RESPONSE Records
   to any particular QUERY Record MUST occur in the same Response
   Message.  If a Pull Directory holds more mappings for a queried
   address than will fit into one Response Message, it selects which
   mappings to include, by some method outside the scope of this
   document, and sets the overflow flag (OV) in all of the
   RESPONSE Records responding to that Query Address.

   See Section 3.6 for a discussion of how errors are handled.

3.2.2.2.  Pull Directory Forwarding

   Query Messages with QTYPEs 2 and 5 are interpreted and handled as
   described below.  In these cases, if the information implicitly
   sought is not in the directory and the FR flag in the Query Message
   was 1 (one), the provided frame is forwarded by the Pull Directory
   server as a multi-destination TRILL Data packet with the ingress
   nickname of the Pull Directory server (or proxy, if it is hosted on
   an end station) in the TRILL Header.  If the FR flag is 0, the frame
   is not forwarded in this case.

   If there was no error in the handling of the encapsulating
   Query Message, the Pull Directory server forwards the frame inside
   that QUERY Record, after modifying it in some cases, as described
   below:

   ARP: When QTYPE is 2 and the Ethertype in the QUERY Record indicates
      that an ARP [RFC826] frame is included in the Record:
      The ar$op field MUST be ares_op$REQUEST, and for the response
      described in Section 3.2.2.1, this is treated as a query for the
      target protocol address, where the AFN of that address is given by
      ar$pro.  (ARP fields and value names with embedded dollar signs
      ("$") are specified in [RFC826].)  If (1) ar$op is not
      ares_op$REQUEST, (2) the ARP is malformed, or (3) the query fails,
      an error is returned.  Otherwise, the ARP is modified into the
      appropriate ARP response, which is then sent by the Pull Directory
      server as a TRILL Data packet.

   ND/SEND: When QTYPE is 2 and the Ethertype in the QUERY Record
      indicates that an IPv6 ND [RFC4861] or SEND [RFC3971] frame is
      included in the Record:
      Only Neighbor Solicitation ND frames (corresponding to an ARP
      query) are allowed.  An error is returned for other ND frames or
      if the target address is not found.  Otherwise, if the ND is not a



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      SEND, an ND Neighbor Advertisement response is returned by the
      Pull Directory server as a TRILL Data packet.  In the case of
      SEND, an error is returned indicating that a SEND frame was
      received by the Pull Directory, and the Pull Directory then either
      (1) forwards the SEND frame to the holder of the IPv6 address if
      that information is in the directory or (2) multicasts the
      SEND frame.

   RARP: When QTYPE is 2 and the Ethertype in the QUERY Record indicates
      that a RARP [RFC903] frame is included in the Record:
      If the ar$op field is ares_op$REQUEST, the frame is handled as an
      ARP, as described above.  Otherwise, the ar$op field MUST be
      "reverse request", and for the response described in
      Section 3.2.2.1, this is treated as a query for the target
      hardware address, where the AFN of that address is given by
      ar$hrd.  (See [RFC826] for RARP fields.)  If (1) ar$op is not one
      of these values, (2) the RARP is malformed, or (3) the query
      fails, an error is returned.  Otherwise, the RARP is modified into
      the appropriate RARP response, which is then unicast by the Pull
      Directory server as a TRILL Data packet to the source hardware MAC
      address.

   MacDA: When QTYPE is 5, indicating that a frame is provided in the
      QUERY Record whose destination MAC address TRILL switch attachment
      is unknown, the only requirement is that this MAC address has to
      be unicast.  The Ethertype in the QUERY Record is ignored.  If
      this MAC address is a group address, an error is returned.  In the
      case of Pull Directory Response Messages (Section 3.2.2.1), this
      MAC address is treated as a query for the MacDA.  In the creation
      of the response described in Section 3.2.2.1, the query is treated
      as a query for this MAC address.  If the Pull Directory contains
      TRILL switch attachment information for the MAC address in the
      Data Label of the Query Message, it forwards the frame to that
      switch in a unicast TRILL Data packet.

3.3.  Cache Consistency

   Unless it sends all responses with a Lifetime of 0, a Pull Directory
   MUST take action, by sending Update Messages, to minimize the amount
   of time that a TRILL switch will continue to use stale information
   from that Pull Directory.  The formats of Update Messages and the
   Acknowledge Messages used to respond to Update Messages are given in
   Sections 3.3.1 and 3.3.2, respectively.








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   A Pull Directory server MUST maintain one of three sets of records
   concerning possible cached data at clients of that server.  These are
   numbered and listed below in order of increasing specificity:

   Method 1, Least Specific.  An overall record, per Data Label, of when
      the last positive Response Data sent will expire and when the last
      negative response sent will expire; the records are retained until
      such expiration.

      Pro: Minimizes the record-keeping burden on the Pull Directory
         server.

      Con: Increases the volume of and overhead due to (1) spontaneous
         Update Messages and (2) unnecessarily invalidating cached
         information.

   Method 2, Medium Specificity.  For each unit of data (Interface
      Addresses APPsub-TLV (IA APPsub-TLV) Address Set [RFC7961]) held
      by the server, record when the last response sent with that
      positive Response Data will expire.  In addition, record each
      address about which a negative response was sent by the server and
      when the last such negative response will expire.  Each such
      record of a positive or negative response is discarded upon
      expiration.

      Pros/Cons: An intermediate level of detail in server
         record-keeping; also, an intermediate volume of, and overhead
         due to, spontaneous Update Messages with some unnecessary
         invalidation of cached information.

   Method 3, Most Specific.  For each unit of data held by the server
      (IA APPsub-TLV Address Set [RFC7961]) and each address about which
      a negative response was sent, a list of TRILL switches that were
      sent that data as a positive response or sent a negative response
      for the address, and the expected time to expiration for that data
      or address at each such TRILL switch, assuming that the requester
      cached the response.  Each list entry is retained until such
      expiration time.

      Pros: Minimizes spontaneous Update Messages sent to update pull
         client TRILL switch caches, and minimizes unnecessary
         invalidation of cached information.

      Con: Increased record-keeping burden on the Pull Directory server.







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   RESPONSE Records sent with a zero Lifetime are considered to have
   already expired and so do not need to be tracked.  In all cases,
   there may still be brief periods of time when directory information
   has changed, but information that a pull client has cached has not
   yet been updated or expunged.

   A Pull Directory server might have a limit as to (1) how many TRILL
   switches for which it can maintain detailed expiry information using
   method 3 or (2) how many data units or addresses for which it can
   maintain expiry information using method 2 or the like.  If such
   limits are exceeded, it MUST transition to a lower-numbered method
   but, in all cases, MUST support, at a minimum, method 1 and SHOULD
   support methods 2 and 3.  The use of method 1 may be quite
   inefficient, due to large amounts of cached positive and negative
   information being unnecessarily discarded.

   When data at a Pull Directory is changed, deleted, or added and there
   may be unexpired stale information at a requesting TRILL switch, the
   Pull Directory MUST send an Update Message as discussed below.  The
   sending of such an Update Message MAY be delayed by a configurable
   number of milliseconds (see "DirUpdateDelay" in Section 3.9) to await
   other possible changes that could be included in the same
   Update Message.

   1. If method 1, the least detailed method, is being followed, then
      when any Pull Directory information in a Data Label is changed or
      deleted and there are outstanding cached positive data
      response(s), an all-addresses flush positive data Update Message
      is flooded within that Data Label as an RBridge Channel message.
      If data is added and there are outstanding cached negative
      responses, an all-addresses flush negative message is similarly
      flooded.  A Count field value of 0 in an Update Message indicates
      "all-addresses".  On receiving an all-addresses flooded flush
      positive Update from a Pull Directory server it has used,
      indicated by the F (Flood) and P (Positive) bits being 1 and the
      Count being 0, a TRILL switch discards the cached data responses
      it has for that Data Label.  Similarly, on receiving an
      all-addresses flush negative Update, indicated by the F and
      N (Negative) bits being 1 and the Count being 0, it discards all
      cached negative replies for that Data Label.  A combined flush
      positive and negative can be flooded by having all of the F, P,
      and N bits (see Section 3.3.1) set to 1 and the Count field 0,
      resulting in the discard of all positive and negative cached
      information for the Data Label.

   2. If method 2 is being followed, then a TRILL switch floods
      address-specific positive Update Messages when data that might be
      cached by a querying TRILL switch is changed or deleted and floods



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      address-specific negative Update Messages when data that might be
      cached by a querying TRILL switch is added.  Such messages are
      sent as RBridge Channel messages.  The F bit will be 1; however,
      the Count field will be non-zero, and either the P bit or the
      N bit, but not both, will be 1.  There are actually four possible
      message types that can be flooded:

      a. If data that might still be cached is updated:
         An unsolicited Update Message is sent with the P flag set and
         the Err field 0.  On receipt, the addresses in the RESPONSE
         Records are compared to the addresses for which the receiving
         TRILL switch is holding cached positive information from that
         server.  If they match, the cached information is updated.

      b. If data that might still be cached is deleted:
         An unsolicited Update Message is sent with the P flag set and
         the Err field non-zero, giving the error that would now be
         encountered in attempting to pull information for the relevant
         address from the Pull Directory server.  In this non-zero Err
         field case, the RESPONSE Record(s) differs from non-zero Err
         Reply Message RESPONSE Records in that they do include an
         interface address set.  Any cached positive information for the
         addresses given is deleted, and the negative response is cached
         as per the Lifetime given.

      c. If data for an address for which a negative response was sent
         is added, so that negative response that might still be cached
         is now incorrect:
         An unsolicited Update Message is sent with the N flag set to 1
         and the Err field 0.  The addresses in the RESPONSE Records are
         compared to the addresses for which the receiving TRILL switch
         is holding cached negative information from that server; if
         they match, the cached negative information is deleted, and the
         positive information provided is cached as per the Lifetime
         given.

      d. In the rare case where it is desired to change the Lifetime or
         error associated with negative information that might still be
         cached:
         An unsolicited Update Message is sent with the N flag set to 1
         and the Err field non-zero.  As in case b above, the RESPONSE
         Record(s) gives the relevant addresses.  Any cached negative
         information for the addresses is updated.

   3. If method 3 is being followed, unsolicited Update Messages of the
      same sort are sent as with method 2 above, except that they are
      not normally flooded but unicast only to the specific TRILL
      switches the directory server believes may be holding the cached



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      positive or negative information that needs deletion or updating.
      However, a Pull Directory server MAY flood unsolicited updates
      using method 3 -- for example, if it determines that a
      sufficiently large fraction of the TRILL switches in some Data
      Label are requesters that need to be updated so that flooding is
      more efficient than unicast.

   A Pull Directory server tracking cached information with method 3
   MUST NOT clear the indication that it needs to update cached
   information at a querying TRILL switch until it has either (a) sent
   an Update Message and received a corresponding Acknowledge Message or
   (b) sent a configurable number of updates at a configurable interval
   where these parameters default to three updates 100 milliseconds
   apart (see Section 3.9).

   A Pull Directory server tracking cached information with method 1 or
   method 2 SHOULD NOT clear the indication that it needs to update
   cached information until it has sent an Update Message and received a
   corresponding Acknowledge Message from all of its ESADI neighbors or
   it has sent a number of updates at a configurable interval, as
   specified in the paragraph above.

3.3.1.  Update Message Format

   An Update Message is formatted as a Response Message, with the
   differences described in Section 3.3 above and the following:

   o  The Type field in the message header is set to 3.

   o  The Index field in the RESPONSE Record(s) is set to 0 on
      transmission and ignored on receipt (but the Count field in the
      Update Message header MUST still correctly indicate the number of
      RESPONSE Records present).

   o  The priority with which the message is sent, DirUpdatePriority, is
      configurable and defaults to 5 (see Section 3.9).

   Update Messages are initiated by a Pull Directory server.  The
   Sequence Number space used is controlled by the originating Pull
   Directory server.  This Sequence Number space for Update Messages is
   different from the Sequence Number space used in a Query and the
   corresponding Response that are controlled by the querying
   TRILL switch.








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   The 4-bit Flags field of the message header for an Update Message is
   as follows:

            +---+---+---+---+
            | F | P | N | R |
            +---+---+---+---+

      F: The Flood bit.  If F = 0, the Update Message is unicast.  If
         F = 1, it is multicast to All-Egress-RBridges.

      P, N: Flags used to indicate positive or negative Update Messages.
         P = 1 indicates "positive".  N = 1 indicates "negative".  Both
         may be 1 for a flooded all-addresses Update.

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

   For tracking methods 2 and 3 in Section 3.3, a particular Update
   Message MUST have either the P flag or the N flag set, but not both.
   If both are set, the Update Message MUST be ignored, as this
   combination is only valid for method 1.

3.3.2.  Acknowledge Message Format

   An Acknowledge Message is sent in response to an Update Message to
   confirm receipt or indicate an error, unless response is inhibited by
   rate limiting.  It is formatted as a Response Message, but the Type
   is set to 4.

   If there are no errors in the processing of an Update Message or if
   there is an overall message-level error or a header error in an
   Update Message, the message is echoed back with the Err and
   SubErr fields set appropriately, the Type changed to Acknowledge, and
   a null Records section with the Count field set to 0.

   If there is a record-level error in an Update Message, one or more
   Acknowledge Messages may be returned with the erroneous record(s)
   indicated as discussed in Section 3.6.

   An Acknowledge Message is sent with the same priority as the Update
   Message it acknowledges but not more than a configured priority
   called "DirAckMaxPriority", which defaults to 5 (see Section 3.9).










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3.4.  Summary of Record Formats in Messages

   As specified in Sections 3.2 and 3.3, the Query, Response, Update,
   and Acknowledge Messages can have zero or more repeating Record
   structures under different circumstances, as summarized below.  The
   "Err" column abbreviations in this table have the meanings listed
   below.  "IA APPsub-TLV value" means the value part of the
   IA APPsub-TLV specified in [RFC7961].

                 MBZ = MUST be zero
                 Z   = zero
                 NZ  = non-zero
                 NZM = non-zero message-level error
                 NZR = non-zero record-level error

       Message    Err  Section  Record Structure    Response Data
     -----------  ---  -------  ----------------  -------------------
     Query        MBZ  3.2.1    QUERY Record       -
     Response     Z    3.2.2.1  RESPONSE Record   IA APPsub-TLV value
     Response     NZM  3.2.2.1  null               -
     Response     NZR  3.2.2.1  RESPONSE Record   Records with error
     Update       MBZ  3.3.1    RESPONSE Record   IA APPsub-TLV value
     Acknowledge  Z    3.3.2    null               -
     Acknowledge  NZM  3.3.2    null               -
     Acknowledge  NZR  3.3.2    RESPONSE Record   Records with error

   See Section 3.6 for further details on errors.

3.5.  End Stations and Pull Directories

   A Pull Directory can be hosted on an end station as specified in
   Section 3.5.1.

   An end station can use a Pull Directory as specified in
   Section 3.5.2.  This capability would be useful in supporting an end
   station that performs directory-assisted encapsulation [DirAsstEncap]
   or that is a "Smart Endnode" [SmartEN].

   The native Pull Directory messages used in these cases are as
   specified in Section 3.5.3.  In these cases, the edge RBridge(s) and
   end station(s) involved need to detect each other and exchange some
   control information.  This is accomplished with the TRILL End System
   to Intermediate System (ES-IS) mechanism specified in Section 5.








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3.5.1.  Pull Directory Hosted on an End Station

   Optionally, a Pull Directory actually hosted on an end station MAY be
   supported.  In that case, one or more TRILL switches must act as
   indirect Pull Directory servers.  That is, they host a Pull Directory
   server, which is seen by other TRILL switches in the campus, and a
   Pull Directory client, which fetches directory information from one
   or more end-station Pull Directory servers, where at least some of
   the information provided by the Pull Directory server may be
   information fetched from an end station to which it is directly
   connected by the co-located Pull Directory client.  ("Direct
   connection" means a connection not involving any intermediate TRILL
   switches.)

   End stations hosting a Pull Directory server MUST support TRILL ES-IS
   (see Section 5) and advertise the Data Labels for which they are
   providing service in one or more Interested VLANs sub-TLVs or
   Interested Labels sub-TLVs by setting the PUL flag (see Section 7.3).

                                                *  *  *  *  *  *  *
      +---------------+                         *                 *
      | End Station 1 |              +---------------+            *
      | Pull Directory+--------------+ RB1, Pull     |            *
      | Server        |              |      Directory|            *
      +---------------+      +-------+ Client|Server |         +----+
                             |       +---------------+         |RB99|
      +---------------+      |                  *              +----+
      | End Station 2 |   +--+---+   +---------------+            *
      | Pull Directory+---+Bridge+---+ RB2, Pull     |            *
      | Server        |   +--+---+   |      Directory|            *
      +---------------+      |       | Client|Server |            *
                             |       +---------------+            *
                             |                  *        TRILL    *
                             .                  *        Campus   *
                             .                  *                 *
                             .                  *  *  *  *  *  *  *

               Figure 2: End-Station Pull Directory Example

   Figure 2 gives an example where RB1 and RB2 advertise themselves to
   the rest of the TRILL campus, such as RB99, as Pull Directory servers
   and obtain at least some of the information they are providing by
   issuing Pull Directory queries to End Stations 1 and/or 2.  This
   example is specific, but many variations are possible.  The box
   labeled "Bridge" in Figure 2 could be replaced by a complex bridged
   LAN or could be a bridgeless LAN through the use of a hub or
   repeater.  Or, end stations might be connected via point-to-point
   links (as shown for End Station 1), including multi-ported



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   end stations connected by point-to-point links to multiple RBridges.
   Although Figure 2 shows two end stations and two RBridges, there
   could be one or more than two RBridges having such indirect Pull
   Directory servers.  Furthermore, there could be one or more than two
   end stations with Pull Directory servers on them.  Each TRILL switch
   acting as an indirect Pull Directory server could then be differently
   configured as to the Data Labels for which it is providing indirect
   service selected from the union of the Data Labels supported by the
   end-station hosted servers and could select from among those
   end-station hosted servers supporting each Data Label the indirect
   server is configured to provide.

   When an indirect Pull Directory server receives Query Messages from
   other TRILL switches, it answers from information it has cached or
   issues Pull Directory requests to end-station Pull Directory servers
   with which it has TRILL ES-IS adjacency to obtain the information.
   Any Response sent by an indirect Pull Directory server MUST NOT have
   a validity time longer than the validity period of the data on which
   it is based.  When an indirect Pull Directory server receives Update
   Messages, it updates its cached information and MUST originate Update
   Messages to any clients that may have mirrors of the cached
   information so updated.

   Since an indirect Pull Directory server discards information it has
   cached from queries to an end-station Pull Directory server if it
   loses adjacency to the server (Section 3.7), if it detects that such
   information may be cached at RBridge clients and has no other source
   for the information, it MUST send Update Messages to those clients
   withdrawing the information.  For this reason, indirect Pull
   Directory servers may wish to query multiple sources, if available,
   and cache multiple copies of returned information from those multiple
   sources.  Then, if one end-station source becomes inaccessible or
   withdraws the information but the indirect Pull Directory server has
   the information from another source, it need not originate Update
   Messages.

3.5.2.  Use of Pull Directory by End Stations

   Some special end stations, such as those discussed in [DirAsstEncap]
   and [SmartEN], may need to access directory information.  How edge
   RBridges provide this optional service is specified below.

   When Pull Directory support is provided by an edge RBridge to end
   stations, the messages used are as specified in Section 3.5.3 below.
   The edge RBridge MUST support TRILL ES-IS (Section 5) and advertises
   the Data Labels for which it offers this service to end stations by





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   setting the Pull Directory flag (PUL) to 1 in its Interested VLANs
   sub-TLV or Interested Labels sub-TLV (see Section 7.3) for that Data
   Label advertised through TRILL ES-IS.

3.5.3.  Native Pull Directory Messages

   The Pull Directory messages used between TRILL switches and end
   stations are native RBridge Channel messages [RFC7178].  These
   RBridge Channel messages use the same Channel Protocol number as the
   inter-RBridge Pull Directory RBridge Channel messages.  The
   Outer.VLAN ID used is the TRILL ES-IS Designated VLAN (see Section 5)
   on the link to the end station.  Since there is no TRILL Header or
   inner Data Label for native RBridge Channel messages, that
   information is added to the Pull Directory message header as
   specified below.

   The protocol-dependent data part of the native RBridge Channel
   message is the same as for inter-RBridge Channel messages, except
   that the 8-byte header described in Section 3.1 is expanded to 12 or
   16 bytes, as follows:

                           1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Ver  | Type  | Flags | Count |      Err      |    SubErr     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence Number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Data Label ... (4 or 8 bytes)                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
      | Type Specific Payload - variable length
      +-+-+- ...

   Fields other than the Data Label field are as defined in Section 3.1.
   The Data Label that normally appears right after the Inner.MacSA of
   the RBridge Channel Pull Directory message appears in the Data Label
   field of the Pull Directory message header in the native RBridge
   Channel message version.  This Data Label appears in a native Query
   Message, to be reflected in a Response Message, or it might appear in
   a native Update to be reflected in an Acknowledge Message.  Since the
   appropriate VLAN or FGL [RFC7172] Ethertype is included, the length
   of the Data Label can be determined from the first 2 bytes.









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3.6.  Pull Directory Message Errors

   A non-zero Err field in the Pull Directory Response or Acknowledge
   Message header indicates an error message.

   If there is an error that applies to an entire Query or Update
   Message or its header, as indicated by the range of the value of the
   Err field, then the QUERY Records probably were not even looked at by
   the Pull Directory server and would provide no additional information
   in the Response or Acknowledge Message.  Therefore, the Records
   section of the response to a Query Message or Update Message is
   omitted, and the Count field is set to 0 in the Response or
   Acknowledge Message.

   If errors occur at the QUERY Record level for a Query Message, they
   MUST be reported in a Response Message separate from the results of
   any successful non-erroneous QUERY Records.  If multiple
   QUERY Records in a Query Message have different errors, they MUST be
   reported in separate Response Messages.  If multiple QUERY Records in
   a Query Message have the same error, this error response MAY be
   reported in one or multiple Response Messages.  In an error Response
   Message, the QUERY Record or Records being responded to appear,
   expanded by the Lifetime for which the server thinks the error might
   persist (usually 2**16 - 1, which indicates "indefinitely") and with
   their Index inserted, as the RESPONSE Record or Records.

   If errors occur at the RESPONSE Record level for an Update Message,
   they MUST be reported in an Acknowledge Message separate from the
   acknowledgment of any non-erroneous RESPONSE Records.  If multiple
   RESPONSE Records in an Update have different errors, they MUST be
   reported in separate Acknowledge Messages.  If multiple
   RESPONSE Records in an Update Message have the same error, this error
   response MAY be reported in one or multiple Acknowledge Messages.  In
   an error Acknowledge Message, the RESPONSE Record or Records being
   responded to appear, expanded by the time for which the server thinks
   the error might persist and with their Index inserted, as a
   RESPONSE Record or Records.

   Err values 1 through 126 are available for encoding errors at the
   Request Message or Update Message level.  Err values 128 through 254
   are available for encoding errors at the QUERY Record or
   RESPONSE Record level.  The SubErr field is available for providing
   more detail on errors.  The meaning of a SubErr field value
   depends on the value of the Err field.







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3.6.1.  Error Codes

   The following table lists error code values for the Err field, their
   meanings, and whether they apply at the message level or the
   record level.

    Err       Level     Meaning
   -------   -------    -----------------------------------------------
       0        -       No Error

       1     Message    Unknown or reserved Query Message field value
       2     Message    Request Message/data too short
       3     Message    Unknown or reserved Update Message field value
       4     Message    Update Message/data too short
   5-126     Message    Unassigned
     127        -       Reserved

     128     Record     Unknown or reserved QUERY Record field value
     129     Record     QUERY Record truncated
     130     Record     Address not found
     131     Record     Unknown or reserved RESPONSE Record field value
     132     Record     RESPONSE Record truncated
   133-254   Record     Unassigned
     255        -       Reserved

   Note that some error codes are for overall message-level errors,
   while some are for errors in the repeating records that occur in
   messages.

3.6.2.  Sub-errors under Error Codes 1 and 3

   The following sub-errors are specified under error codes 1 and 3:

      SubErr   Field with Error
      ------   -------------------------------------------
          0     Unspecified
          1     Version not understood (see Section 3.1.1)
          2     Unknown Type field value
          3     Specified Data Label not being served
      4-254     Unassigned
        255     Reserved










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3.6.3.  Sub-errors under Error Codes 128 and 131

   The following sub-errors are specified under error codes 128 and 131:

      SubErr   Field with Error
      ------   ----------------------------------------------------
          0     Unspecified
          1     Unknown AFN field value
          2     Unknown or Reserved QTYPE field value
          3     Invalid or inconsistent SIZE field value
          4     Invalid frame for QTYPE 2 (other than SEND)
          5     SEND frame sent as QTYPE 2
          6     Invalid frame for QTYPE 5 (such as multicast MacDA)
      7-254     Unassigned
        255     Reserved

3.7.  Additional Pull Details

   A Pull Directory client MUST be able to detect, by tracking
   link-state changes, when a Pull Directory server is no longer
   accessible (data reachable [RFC7780] for the inter-RBridge case or
   TRILL ES-IS (Section 5) adjacent for the end-station-to-RBridge case)
   and MUST promptly discard all pull responses it is retaining from
   that server, as it can no longer receive cache consistency Update
   Messages from the server.

   A secondary Pull Directory server is one that obtains its data from a
   primary directory server.  See the discussion in Section 2.6
   regarding the transfer of directory information from the
   primary server to the secondary server.

3.8.  The "No Data" Flag

   In the TRILL base protocol [RFC6325] as extended for FGL [RFC7172],
   the mere presence of any Interested VLANs sub-TLVs or Interested
   Labels sub-TLVs in the LSP of a TRILL switch indicates connection to
   end stations in the VLAN(s) or FGL(s) listed and thus a need to
   receive multi-destination traffic in those Data Labels.  However,
   with Pull Directories, advertising that you are a directory server
   requires using these sub-TLVs to indicate the Data Label(s) you are
   serving.

   If a directory server does not wish to receive multi-destination
   TRILL Data packets for the Data Labels it lists in one of the
   Interested VLANs or Interested Labels (FGLs) sub-TLVs (see
   Section 1.2), it sets the No Data (NOD) bit to 1 (see Section 7.3).
   This means that data on a distribution tree may be pruned so as not
   to reach the "No Data" TRILL switch as long as there are no TRILL



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   switches interested in the Data Label that are beyond the No Data
   TRILL switch on that distribution tree.  The NOD bit is backward
   compatible, as TRILL switches ignorant of it will simply not prune
   when they could; this is safe, although it may cause increased link
   utilization by some TRILL switches sending multi-destination traffic
   where it is not needed.

   Push Directories advertise themselves inside ESADI, which normally
   requires the ability to send and receive multi-destination TRILL Data
   packets but can be implemented with serial unicast.

   An example of a TRILL switch serving as a directory that might not
   want multi-destination traffic in some Data Labels would be a TRILL
   switch that does not offer end-station service for any of the Data
   Labels for which it is serving as a directory and is

   -  a Pull Directory and/or

   -  a Push Directory for one or more Data Labels, where all of the
      ESADI traffic for those Data Labels will be handled by unicast
      ESADI [RFC7357].

   A Push Directory MUST NOT set the NOD bit for a Data Label if it
   needs to communicate via multi-destination ESADI or RBridge Channel
   PDUs in that Data Label, since such PDUs look like TRILL Data packets
   to transit TRILL switches and are likely to be incorrectly pruned if
   the NOD bit was set.
























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3.9.  Pull Directory Service Configuration

   The following per-RBridge scalar configuration parameters are
   available for controlling Pull Directory service behavior.  In
   addition, there is a configurable mapping, per Data Label, from the
   priority of a native frame being ingressed to the priority of any
   Pull Directory query it causes.  The default mapping depends on the
   client strategy, as described in Section 4.

             Name         Default            Section   Note Below
      ------------------  ----------------   -------   ----------

      DirQueryTimeout     100 milliseconds   3.2.1          1
      DirQueryRetries       3                3.2.1          1
      DirGenQPriority       5                3.2.1          2

      DirRespMaxPriority    6                3.2.2.1        3

      DirUpdateDelay       50 milliseconds   3.3
      DirUpdatePriority     5                3.3.1
      DirUpdateTimeout    100 milliseconds   3.3.3
      DirUpdateRetries      3                3.3.3

      DirAckMaxPriority     5                3.3.2          4

      Note 1: Pull Directory Query client timeout waiting for response
         and maximum number of retries.

      Note 2: Priority for client-generated requests (such as a query to
         refresh cached information).

      Note 3: Pull Directory Response Messages SHOULD NOT be sent with
         priority 7, as that priority SHOULD be reserved for messages
         critical to network connectivity.

      Note 4: Pull Directory Acknowledge Messages SHOULD NOT be sent
         with priority 7, as that priority SHOULD be reserved for
         messages critical to network connectivity.

4.  Directory Use Strategies and Push-Pull Hybrids

   For some edge nodes that have a great number of Data Labels enabled,
   managing the MAC and Data Label <-> Edge RBridge mapping for hosts
   under all those Data Labels can be a challenge.  This is especially
   true for data-center gateway nodes, which need to communicate with
   many, if not all, Data Labels.





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   For those edge TRILL switch nodes, a hybrid model should be
   considered.  That is, the Push Model is used for some Data Labels or
   addresses within a Data Label, while the Pull Model is used for other
   Data Labels or addresses within a Data Label.  The network operator
   decides, via configuration, which Data Labels' mapping entries are
   pushed down from directories and which Data Labels' mapping entries
   are pulled.

   For example, assume a data center where hosts in specific Data
   Labels, say VLANs 1 through 100, communicate regularly with external
   peers.  The mapping entries for those 100 VLANs should probably be
   pushed down to the data-center gateway routers.  For hosts in other
   Data Labels that only communicate with external peers occasionally
   for management interfacing, the mapping entries for those VLANs
   should be pulled down from the directory when needed.

   Similarly, within a Data Label, it could be that some addresses, such
   as the addresses of gateways, files, DNS, or database server hosts
   are commonly referenced by most other hosts but those other hosts,
   perhaps compute engines, are typically only referenced by a few hosts
   in that Data Label.  In that case, the address information for the
   commonly referenced hosts could be pushed as an incomplete directory,
   while the addresses of the others are pulled when needed.

   The mechanisms described in this document for Push and Pull Directory
   services make it easy to use Push for some Data Labels or addresses
   and Pull for others.  In fact, different TRILL switches can even be
   configured so that some use Push Directory services and some use Pull
   Directory services for the same Data Label if both Push and Pull
   Directory services are available for that Data Label.  Also, there
   can be Data Labels for which directory services are not used at all.

   There are a wide variety of strategies that a TRILL switch can adopt
   for making use of directory assistance.  A few suggestions are given
   below.

   -  Even if a TRILL switch will normally be operating with information
      from a complete Push Directory server, there will be a period of
      time when it first comes up before the information it holds is
      complete.  Or, it could be that the only Push Directories that can
      push information to it are incomplete or that they are just
      starting and may not yet have pushed the entire directory.  Thus,
      it is RECOMMENDED that all TRILL switches have a strategy for
      dealing with the situation where they do not have complete
      directory information.  Examples are to send a Pull Directory
      query or to revert to the behavior described in [RFC6325].





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   -  If a TRILL switch receives a native frame X resulting in seeking
      directory information, a choice needs to be made as to what to do
      if it does not already have the directory information it needs.
      In particular, it could (1) immediately flood the TRILL Data
      packet resulting from ingressing X in parallel with seeking the
      directory information, (2) flood that TRILL Data packet after a
      delay, if it fails to obtain the directory information, or
      (3) discard X if it fails to obtain the information.  The choice
      might depend on the priority of frame X, since the higher that
      priority the more urgent the frame typically is, and the greater
      the probability of harm in delaying it.  If a Pull Directory
      request is sent, it is RECOMMENDED that its priority be derived
      from the priority of frame X according to the table below;
      however, it SHOULD be possible, on a per-TRILL-switch basis, to
      configure the second two columns of this table.

          Ingressed     If Flooded    If Flooded
          Priority      Immediately   After Delay
          --------      -----------   -----------
            7             5             6
            6             5             6
            5             4             5
            4             3             4
            3             2             3
            2             0             2
            0             1             0
            1             1             1

      Note: The odd-looking ordering of numbers towards the bottom of
      the columns above is because priority 1 is lower than priority
      zero.  That is to say, the values in the first column are in
      priority order.  They will look more logical if you think of "0"
      as being "1.5".

   Priority 7 is normally only used for urgent messages critical to
   adjacency and so SHOULD NOT be the default for directory traffic.
   Unsolicited updates are sent with a priority that is configured per
   Data Label and that defaults to priority 5.

5.  TRILL ES-IS

   TRILL ES-IS (End System to Intermediate System) is a variation of
   TRILL IS-IS [RFC7176] [RFC7177] [RFC7780] designed to operate on a
   TRILL link among and between one or more TRILL switches and end
   stations on that link.  TRILL ES-IS is analogous to the ISO/IEC ES-IS
   standard [ISO9542] but is implemented in a significantly different
   way as a variation of TRILL IS-IS, as specified in this section.
   Support of TRILL ES-IS is generally optional for both the TRILL



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   switches and the end stations on a link but may be required to
   support certain features.  At the time of this writing, the only
   features requiring TRILL ES-IS are those listed in this section.

   TRILL ES-IS

   o  is useful for supporting Pull Directory hosting on, or use from,
      end stations (see Section 3.5),

   o  is useful for supporting specialized end stations [DirAsstEncap]
      [SmartEN], and

   o  may have additional future uses.

   The advantages of TRILL ES-IS over simply making an "end station" be
   a TRILL switch include relieving the end station of having to
   maintain a copy of the core link-state database (LSPs) and of having
   to perform routing calculations or having the ability to forward
   traffic.

   Except as provided below in this section, TRILL ES-IS PDUs and TLVs
   are the same as TRILL IS-IS PDUs and TLVs.

5.1.  PDUs and System IDs

   All TRILL ES-IS PDUs (except some MTU-probe and MTU-ack PDUs, which
   may be unicast) are multicast using the TRILL-ES-IS multicast MAC
   address (see Section 7.6).  This use of a different multicast address
   assures that TRILL ES-IS and TRILL IS-IS PDUs will not be confused
   for one another.

   Because end stations do not have IS-IS System IDs, TRILL ES-IS uses
   port MAC addresses in their place.  This is convenient, since MAC
   addresses are 48-bit and almost all IS-IS implementations use 48-bit
   System IDs.  Logically, TRILL IS-IS operates between the TRILL
   switches in a TRILL campus as identified by the System ID, while
   TRILL ES-IS operates between Ethernet ports on an Ethernet link
   (which may be a bridged LAN) as identified by the MAC address
   [RFC6325].

   As System IDs of TRILL switches in a campus are required to be
   unique, so the MAC addresses of TRILL ES-IS ports on a link MUST be
   unique.








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5.2.  Adjacency, DRB Election, Port IDs, Hellos, and TLVs

   TRILL ES-IS adjacency formation and Designated RBridge (DRB) election
   operate between the ports on the link as specified in [RFC7177] for a
   broadcast link.  The DRB specifies an ES-IS Designated VLAN for the
   link.  Adjacency determination, DRB election, and Designated VLANs as
   described in this section are distinct from TRILL IS-IS adjacency,
   DRB election, and Designated VLANs.

   Although the "Report state" [RFC7177] exists for TRILL ES-IS
   adjacencies, such adjacencies are only reported in TRILL ES-IS LSPs,
   not in any TRILL IS-IS LSPs.

   End stations supporting TRILL ES-IS MUST assign a unique Port ID to
   each of their TRILL ES-IS ports; the Port ID appears in the TRILL
   ES-IS Hellos they send.

   TRILL ES-IS has nothing to do with Appointed Forwarders.  The
   Appointed Forwarders sub-TLV and the VLANs Appointed sub-TLV
   [RFC7176] are not used and SHOULD NOT be sent in TRILL ES-IS; if such
   a sub-TLV is received in TRILL ES-IS, it is ignored.  (The Appointed
   Forwarders on a link are determined as specified in [RFC8139], using
   TRILL IS-IS.)

   Although some of the ports sending TRILL ES-IS PDUs are on end
   stations and thus not on routers (TRILL switches), they nevertheless
   may make use of the Router CAPABILITY (#242) [RFC7981] and
   MT-Capability (#144) [RFC6329] IS-IS TLVs to indicate capabilities as
   specified in [RFC7176].

   TRILL ES-IS Hellos are like TRILL IS-IS Hellos, but note the
   following: in the Special VLANs and Flags sub-TLV [RFC7176], any
   TRILL switches advertise a nickname they own, but for end stations,
   that field MUST be sent as zero and ignored on receipt.  In addition,
   in the Special VLANs and Flags sub-TLV (Section 2.2.1 of [RFC7176])
   in a TRILL ES-IS Hello, the AF and TR flag bits MUST be sent as zero,
   the AC flag bit MUST be sent as one (1), and all three are ignored
   on receipt.













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5.3.  Link State

   The only link-state transmission and synchronization that occur in
   TRILL ES-IS are for E-L1CS (Extended Level 1 Circuit Scope) PDUs
   [RFC7356].  In particular, the end-station Ethernet ports supporting
   TRILL ES-IS do not support the core TRILL IS-IS LSPs and do not
   support E-L1FS (Extended Level 1 Flooding Scope) LSPs [RFC7780] (or
   the CSNPs or PSNPs (Partial Sequence Number PDUs) [RFC7356]
   corresponding to either of them).  TLVs and sub-TLVs that would
   otherwise be sent in TRILL IS-IS LSPs or E-L1FS LSPs are instead sent
   in E-L1CS LSPs.

6.  Security Considerations

   For general TRILL security considerations, see [RFC6325].

6.1.  Directory Information Security

   Incorrect directory information can result in a variety of security
   threats, including those listed below.  Directory servers therefore
   need to take care to implement and enforce access control policies
   that are not overly permissive.

   o  Incorrect directory mappings can result in data being delivered to
      the wrong end stations, or set of end stations in the case of
      multi-destination packets, violating security policy.

   o  Missing, incorrect, or inaccessible directory data can result in
      denial of service due to sending data packets to black holes or
      discarding data on ingress due to incorrect information that their
      destinations are not reachable or that their source addresses are
      forged.

   For these reasons, whatever server or end station the directory
   information resides on, it needs to be protected from unauthorized
   modification.  Parties authorized to modify directory data can
   violate availability and integrity policies.

6.2.  Directory Confidentiality and Privacy

   In implementations of the base TRILL protocol [RFC6325] [RFC7780],
   RBridges deal almost exclusively with MAC addresses.  The use of
   directories to map to/from IP addresses means that RBridges deal more
   actively with IP addresses as well.  But RBridges in any case would
   be exposed to plain-text ARP/ND/SEND/IP traffic and so can see all
   this addressing metadata.  So, this more-explicit dealing with IP
   addresses has little effect on the privacy of end-station traffic.




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   Parties authorized to read directory data can violate privacy
   policies for such data.

6.3.  Directory Message Security Considerations

   Push Directory data is distributed through ESADI-LSPs [RFC7357].
   ESADI is built on IS-IS, and such data can thus be authenticated with
   the widely implemented and deployed IS-IS PDU security.  This
   mechanism provides authentication and integrity protection.  See
   [RFC5304], [RFC5310], and the Security Considerations section of
   [RFC7357].

   Pull Directory queries and responses are transmitted as
   RBridge-to-RBridge or native RBridge Channel messages [RFC7178].
   Such messages can be secured by the mechanisms specified in
   [RFC7978].  These mechanisms can provide authentication and
   confidentiality protection.  At the time of this writing, these
   security mechanisms are believed to be less widely implemented than
   IS-IS security.

7.  IANA Considerations

7.1.  ESADI-Parameter Data Extensions

   IANA has created a subregistry in the "TRILL Parameters" registry
   as follows:

      Subregistry: ESADI-Parameter APPsub-TLV Flag Bits
      Registration Procedure(s): Standards Action
      References: [RFC7357] [RFC8171]

         Bit  Mnemonic  Description                    Reference
         ---  --------  ----------------------------   ---------------
           0    UN      Supports Unicast ESADI         ESADI [RFC7357]
         1-2    PDSS    Push Directory Server Status   [RFC8171]
         3-7    -       Unassigned

   In addition, the ESADI-Parameter APPsub-TLV is optionally extended,
   as provided in its original specification in ESADI [RFC7357], by
   1 byte as shown below.  Therefore, [RFC8171] has also been added as a
   second reference to the ESADI-Parameter APPsub-TLV in the "TRILL
   APPsub-TLV Types under IS-IS TLV 251 Application Identifier 1"
   registry.








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             +-+-+-+-+-+-+-+-+
             | Type          |           (1 byte)
             +-+-+-+-+-+-+-+-+
             | Length        |           (1 byte)
             +-+-+-+-+-+-+-+-+
             |R| Priority    |           (1 byte)
             +-+-+-+-+-+-+-+-+
             | CSNP Time     |           (1 byte)
             +-+-+-+-+-+-+-+-+
             | Flags         |           (1 byte)
             +---------------+
             |PushDirPriority|           (optional, 1 byte)
             +---------------+
             | Reserved for              (variable)
             |  expansion
             +-+-+-+-...

   The meanings of all the fields are as specified in ESADI [RFC7357],
   except that the added PushDirPriority is the priority of the
   advertising ESADI instance to be a Push Directory as described in
   Section 2.3.  If the PushDirPriority field is not present
   (Length = 3), it is treated as if it were 0x3F.  0x3F is also the
   value used and placed here by a TRILL switch whose priority to be a
   Push Directory has not been configured.

7.2.  RBridge Channel Protocol Numbers

   IANA has assigned a new RBridge Channel Protocol number (0x005) from
   the range assignable by Standards Action [RFC5226] and updated the
   subregistry accordingly in the "TRILL Parameters" registry.  The
   description is "Pull Directory Services".  The reference is
   [RFC8171].

7.3.  The Pull Directory (PUL) and No Data (NOD) Bits

   IANA has assigned a previously reserved bit in the Interested VLANs
   field of the Interested VLANs sub-TLV and the Interested Labels field
   of the Interested Labels sub-TLV [RFC7176] to indicate a Pull
   Directory server (PUL).  This bit has been added, with this document
   as a reference, to the "Interested VLANs Flag Bits" and "Interested
   Labels Flag Bits" subregistries created by [RFC7357], as shown below.










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   IANA has assigned a previously reserved bit in the Interested VLANs
   field of the Interested VLANs sub-TLV and the Interested Labels field
   of the Interested Labels sub-TLV [RFC7176] to indicate No Data (NOD)
   (see Section 3.8).  This bit has been added, with this document as a
   reference, to the "Interested VLANs Flag Bits" and "Interested Labels
   Flag Bits" subregistries created by [RFC7357], as shown below.

   The bits are as follows:

      Registry: Interested VLANs Flag Bits

      Bit Mnemonic  Description     Reference
      --- -------- --------------  ---------------
       18    PUL   Pull Directory  [RFC8171]
       19    NOD   No Data         [RFC8171]

      Registry: Interested Labels Flag Bits

      Bit Mnemonic  Description     Reference
      --- -------- --------------  ---------------
        6    PUL   Pull Directory  [RFC8171]
        7    NOD   No Data         [RFC8171]

7.4.  TRILL Pull Directory QTYPEs

   IANA has created a new registry as follows:

      Name: TRILL Pull Directory Query Types (QTYPEs)
      Registration Procedure(s): IETF Review
      Reference: [RFC8171]
      Initial contents as in Section 3.2.1.

7.5.  Pull Directory Error Code Registries

   IANA has created a new registry and two new indented subregistries
   as follows:

      Registry
         Name: TRILL Pull Directory Errors
         Registration Procedure(s): IETF Review
         Reference: [RFC8171]

         Initial contents as in Section 3.6.1.








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         Subregistry
            Name: Sub-codes for TRILL Pull Directory Errors 1 and 3
            Registration Procedure(s): Expert Review
            Reference: [RFC8171]

            Initial contents as in Section 3.6.2.

         Subregistry
            Name: Sub-codes for TRILL Pull Directory Errors 128 and 131
            Registration Procedure(s): Expert Review
            Reference: [RFC8171]

            Initial contents as in Section 3.6.3.

7.6.  TRILL-ES-IS MAC Address

   IANA has assigned a TRILL multicast MAC address (01-80-C2-00-00-47)
   from the "TRILL Multicast Addresses" registry.  The description is
   "TRILL-ES-IS".  The reference is [RFC8171].

8.  References

8.1.  Normative References

   [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>.

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,
              <http://www.rfc-editor.org/info/rfc3971>.







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   [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>.

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, DOI 10.17487/RFC5304,
              October 2008, <http://www.rfc-editor.org/info/rfc5304>.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, DOI 10.17487/RFC5310,
              February 2009, <http://www.rfc-editor.org/info/rfc5310>.

   [RFC6165]  Banerjee, A. and D. Ward, "Extensions to IS-IS for Layer-2
              Systems", RFC 6165, DOI 10.17487/RFC6165, April 2011,
              <http://www.rfc-editor.org/info/rfc6165>.

   [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>.

   [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,
              DOI 10.17487/RFC6329, April 2012,
              <http://www.rfc-editor.org/info/rfc6329>.

   [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>.

   [RFC7176]  Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt,
              D., and A. Banerjee, "Transparent Interconnection of Lots
              of Links (TRILL) Use of IS-IS", RFC 7176,
              DOI 10.17487/RFC7176, May 2014,
              <http://www.rfc-editor.org/info/rfc7176>.






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   [RFC7177]  Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H., and
              V. Manral, "Transparent Interconnection of Lots of Links
              (TRILL): Adjacency", RFC 7177, DOI 10.17487/RFC7177,
              May 2014, <http://www.rfc-editor.org/info/rfc7177>.

   [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>.

   [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>.

   [RFC7961]  Eastlake 3rd, D. and L. Yizhou, "Transparent
              Interconnection of Lots of Links (TRILL): Interface
              Addresses APPsub-TLV", RFC 7961, DOI 10.17487/RFC7961,
              August 2016, <http://www.rfc-editor.org/info/rfc7961>.

   [RFC7981]  Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
              for Advertising Router Information", RFC 7981,
              DOI 10.17487/RFC7981, October 2016,
              <http://www.rfc-editor.org/info/rfc7981>.

   [RFC8139]  Eastlake 3rd, D., Li, Y., Umair, M., Banerjee, A., and F.
              Hu, "Transparent Interconnection of Lots of Links (TRILL):
              Appointed Forwarders", RFC 8139, DOI 10.17487/RFC7961,
              June 2017, <http://www.rfc-editor.org/info/rfc8139>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in
              RFC 2119 Key Words", BCP 14, RFC 8174,
              DOI 10.17487/RFC8174, May 2017,
              <http://www.rfc-editor.org/info/rfc8174>.




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8.2.  Informative References

   [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>.

   [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>.

   [RFC7978]  Eastlake 3rd, D., Umair, M., and Y. Li, "Transparent
              Interconnection of Lots of Links (TRILL): RBridge Channel
              Header Extension", RFC 7978, DOI 10.17487/RFC7978,
              September 2016, <http://www.rfc-editor.org/info/rfc7978>.

   [ARPND]    Li, Y., Eastlake 3rd, D., Dunbar, L., Perlman, R., and M.
              Umair, "TRILL: ARP/ND Optimization", Work in Progress,
              draft-ietf-trill-arp-optimization-08, April 2017.

   [DirAsstEncap]
              Dunbar, L., Eastlake 3rd, D., and R. Perlman, "Directory
              Assisted TRILL Encapsulation", Work in Progress,
              draft-ietf-trill-directory-assisted-encap-05, May 2017.

   [ISO9542]  ISO 9542:1988, "Information processing systems --
              Telecommunications and information exchange between
              systems -- End system to Intermediate system routeing
              exchange protocol for use in conjunction with the Protocol
              for providing the connectionless-mode network service
              (ISO 8473)", August 1988.

   [SmartEN]  Perlman, R., Hu, F., Eastlake 3rd, D., Krupakaran, K., and
              T. Liao, "TRILL Smart Endnodes", Work in Progress,
              draft-ietf-trill-smart-endnodes-05, February 2017.

   [X.233]    International Telecommunication Union, ITU-T
              Recommendation X.233: "Information technology - Protocol
              for providing the connectionless-mode network service:
              Protocol specification", August 1997,
              <https://www.itu.int/rec/T-REC-X.233/en>.









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Acknowledgments

   The contributions of the following persons are gratefully
   acknowledged:

      Amanda Baber, Matthew Bocci, Alissa Cooper, Stephen Farrell,
      Daniel Franke, Igor Gashinsky, Joel Halpern, Susan Hares, Alexey
      Melnikov, Gayle Noble, and Tianran Zhou.

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


   Linda Dunbar
   Huawei Technologies
   5430 Legacy Drive, Suite #175
   Plano, TX  75024
   United States of America
   Phone: +1-469-277-5840
   Email: ldunbar@huawei.com


   Radia Perlman
   EMC
   2010 256th Avenue NE, #200
   Bellevue, WA  98007
   United States of America
   Email: Radia@alum.mit.edu


   Yizhou Li
   Huawei Technologies
   101 Software Avenue
   Nanjing  210012
   China
   Phone: +86-25-56622310
   Email: liyizhou@huawei.com







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