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rfc:rfc8171

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.

Eastlake, et al. Standards Track [Page 1] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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

Eastlake, et al. Standards Track [Page 2] RFC 8171 TRILL: Directory Service Mechanisms June 2017

    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

Eastlake, et al. Standards Track [Page 3] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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.

Eastlake, et al. Standards Track [Page 4] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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).

Eastlake, et al. Standards Track [Page 5] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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.

Eastlake, et al. Standards Track [Page 6] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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

Eastlake, et al. Standards Track [Page 7] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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

Eastlake, et al. Standards Track [Page 8] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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.

Eastlake, et al. Standards Track [Page 9] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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

Eastlake, et al. Standards Track [Page 10] RFC 8171 TRILL: Directory Service Mechanisms June 2017

    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.

Eastlake, et al. Standards Track [Page 11] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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.

Eastlake, et al. Standards Track [Page 12] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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>

Eastlake, et al. Standards Track [Page 13] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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

Eastlake, et al. Standards Track [Page 14] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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.

Eastlake, et al. Standards Track [Page 15] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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

Eastlake, et al. Standards Track [Page 16] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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

Eastlake, et al. Standards Track [Page 17] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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.

Eastlake, et al. Standards Track [Page 18] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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.

Eastlake, et al. Standards Track [Page 19] RFC 8171 TRILL: Directory Service Mechanisms June 2017

    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.

Eastlake, et al. Standards Track [Page 20] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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.)

Eastlake, et al. Standards Track [Page 21] RFC 8171 TRILL: Directory Service Mechanisms June 2017

    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.

Eastlake, et al. Standards Track [Page 22] RFC 8171 TRILL: Directory Service Mechanisms June 2017

       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.

Eastlake, et al. Standards Track [Page 23] RFC 8171 TRILL: Directory Service Mechanisms June 2017

       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).

Eastlake, et al. Standards Track [Page 24] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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

Eastlake, et al. Standards Track [Page 25] RFC 8171 TRILL: Directory Service Mechanisms June 2017

          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:
  1. 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.
  1. 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.
  1. 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.

Eastlake, et al. Standards Track [Page 26] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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

Eastlake, et al. Standards Track [Page 27] RFC 8171 TRILL: Directory Service Mechanisms June 2017

    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.

Eastlake, et al. Standards Track [Page 28] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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.

Eastlake, et al. Standards Track [Page 29] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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

Eastlake, et al. Standards Track [Page 30] RFC 8171 TRILL: Directory Service Mechanisms June 2017

    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

Eastlake, et al. Standards Track [Page 31] RFC 8171 TRILL: Directory Service Mechanisms June 2017

    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.

Eastlake, et al. Standards Track [Page 32] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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).

Eastlake, et al. Standards Track [Page 33] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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.

Eastlake, et al. Standards Track [Page 34] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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

Eastlake, et al. Standards Track [Page 35] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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

Eastlake, et al. Standards Track [Page 36] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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.

Eastlake, et al. Standards Track [Page 37] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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.

Eastlake, et al. Standards Track [Page 38] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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

Eastlake, et al. Standards Track [Page 39] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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

Eastlake, et al. Standards Track [Page 40] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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
  1. a Pull Directory and/or
  1. 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.

Eastlake, et al. Standards Track [Page 41] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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.

Eastlake, et al. Standards Track [Page 42] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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.
  1. 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].

Eastlake, et al. Standards Track [Page 43] RFC 8171 TRILL: Directory Service Mechanisms June 2017

  1. 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

Eastlake, et al. Standards Track [Page 44] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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.

Eastlake, et al. Standards Track [Page 45] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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.

Eastlake, et al. Standards Track [Page 46] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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.

Eastlake, et al. Standards Track [Page 47] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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.

Eastlake, et al. Standards Track [Page 48] RFC 8171 TRILL: Directory Service Mechanisms June 2017

           +-+-+-+-+-+-+-+-+
           | 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.

Eastlake, et al. Standards Track [Page 49] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 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.

Eastlake, et al. Standards Track [Page 50] RFC 8171 TRILL: Directory Service Mechanisms June 2017

       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>.

Eastlake, et al. Standards Track [Page 51] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 [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>.

Eastlake, et al. Standards Track [Page 52] RFC 8171 TRILL: Directory Service Mechanisms June 2017

 [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>.

Eastlake, et al. Standards Track [Page 53] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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>.

Eastlake, et al. Standards Track [Page 54] RFC 8171 TRILL: Directory Service Mechanisms June 2017

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

Eastlake, et al. Standards Track [Page 55]

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