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Versions: 00 01 02 03 04 05 06 draft-ietf-trill-directory-assist-mechanisms

INTERNET-DRAFT                                              Linda Dunbar
Intended status: Proposed Standard                       Donald Eastlake
Updates: ESADI                                                    Huawei
                                                           Radia Perlman
                                                                   Intel
                                                          Igor Gashinsky
                                                                   Yahoo
                                                               Yizhou Li
                                                                  Huawei
Expires: April 20, 2014                                 October 21, 2013


              TRILL: Edge Directory Assistance Mechanisms
        <draft-dunbar-trill-scheme-for-directory-assist-06.txt>



Abstract
   This document describes mechanisms for using directory server(s) to
   assist TRILL (Transparent Interconnection of Lots of Links) edge
   switches in reducing multi-destination traffic, particularly ARP/ND
   and unknown unicast flooding.



Status of This Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Distribution of this document is unlimited. Comments should be sent
   to the TRILL working group mailing list.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html. The list of Internet-Draft
   Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.








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Table of Contents

      1. Introduction............................................3
      1.1 Terminology............................................3

      2. Push Model Directory Assistance Mechanisms..............5
      2.1 Requesting Push Service................................5
      2.2 Push Directory Servers.................................5
      2.3 Push Directory Server State Machine....................6
      2.3.1 Push Directory States................................6
      2.3.2 Push Directory Events and Conditions.................7
      2.3.3 State Transition Diagram and Table...................8
      2.4 Additional Push Details...............................10
      2.5 Primary to Secondary Server Push Service..............11

      3. Pull Model Directory Assistance Mechanisms.............12
      3.1 Pull Directory Request Format.........................12
      3.2 Pull Directory Response Format........................15
      3.3 Pull Directory Hosted on an End Station...............18
      3.4 Pull Directory Request Errors.........................19
      3.5 Cache Consistency.....................................20
      3.6 Additional Pull Details...............................22

      4. Events That May Cause Directory Use....................23
      4.1 Forged Native Frame Ingress...........................23
      4.2 Unknown Destination MAC...............................23
      4.3 Address Resolution Protocol (ARP).....................24
      4.4 IPv6 Neighbor Discovery (ND)..........................25
      4.5 Reverse Address Resolution Protocol (RARP)............25

      5. Layer 3 Address Learning...............................26

      6. Directory Use Strategies and Push-Pull Hybrids.........27
      6.1 Strategy Configuration................................27

      7. Security Considerations................................30

      8. IANA Considerations....................................31
      8.1 ESADI-Parameter Data..................................31
      8.2 RBridge Channel Protocol Number.......................32
      8.3 The Pull Directory and No Data Bits...................32

      Acknowledgments...........................................33
      Normative References......................................33
      Informational References..................................34
      Authors' Addresses........................................35






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1. Introduction

   [DirectoryFramework] describes a high-level framework for using
   directory servers to assist TRILL [RFC6325] edge nodes to reduce
   multi-destination ARP/ND and unknown unicast flooding traffic and to
   potentially improve security against address spoofing within a TRILL
   campus.  Because multi-destination traffic becomes an increasing
   burden as a network scales, reducing ARP/ND and unknown unicast
   flooding improves TRILL network scalability. This document describes
   specific mechanisms for directory servers to assist TRILL edge nodes.
   These mechanisms are optional to implement.

   The information held by the Directory(s) is address mapping and
   reachability information.  Most commonly, what MAC address
   [RFC5342bis] corresponds to an IP address within a Data Label (VLAN
   or FGL (Fine Grained Label [RFCfgl])) and from what egress TRILL
   switch (RBridge) (and optionally what specific TRILL switch port)
   that MAC address is reachable. But it could be what IP address
   corresponds to a MAC address or possibly other address mappings or
   reachability. 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 is appropriate for providing the
   directory function or for supplying the Directory(s) with directory
   information.

   Directory services can be offered in a Push or Pull mode. 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. Modes of operation, including hybrid
   Push/Pull, are discussed in Section 4.

   The mechanisms used to initially populate directory data in primary
   servers is beyond the scope of this document. The Push Directory
   service can be used by a primary server to provide Directory data to
   secondary servers as described in Section 2.



1.1 Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [RFC2119].

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

   CP: Complete Push flag bit. See Sections 2 and 6.1 below.


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   CSNP Time: Complete Sequence Number PDU Time. See [ESADI] and Section
         6.1 below.

   Data Label: VLAN or FGL.

   FGL:  Fine Grained Label [RFCfgl].

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

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

   PD: Push Directory flag bit. See Sections 2 and 6.1 below.

   primary server: A Directory server that obtains the information it is
         serving up by a reliable mechanism outside the scope of this
         document but designed to assure the freshness of that
         information. (See secondary server.)

   RBridge: An alternative name for a TRILL switch.

   secondary server: A Directory server that obtains the information it
         is serving up from one or more primary servers.

   tenant: Sometimes used as a synonym for FGL.

   TRILL switch: A device that implements the TRILL protocol.























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2. Push Model Directory Assistance Mechanisms

   In the Push Model [DirectoryFramework], one or more Push Directory
   servers push down the address mapping information for the various
   addresses associated with end station interface and the TRILL
   switches from which those interfaces are reachable [IA]. This service
   is scoped by Data Label (VLAN or FGL [RFCfgl]).  A Push Directory
   also advertises whether or not it believes it has pushed complete
   mapping information for a Data Label. It might be pushing mapping
   information for only a subset of the ports in a Data Label. The Push
   Model uses the [ESADI] protocol as its distribution mechanism.

   With the Push Model, if complete address mapping information for a
   Data Label being pushed is available, a TRILL switch (RBridge) which
   has that complete pushed information can simply drop a native frame
   if the destination unicast MAC address can't be found in the mapping
   information available, instead of flooding it (see Section 2.1). This
   will minimize flooding of packets due to errors or inconsistencies
   but is not practical if directories have incomplete information.



2.1 Requesting Push Service

   In the Push Model, it is necessary to have a way for an RBridge to
   request information from the directory server(s).  RBridges simply
   use the ESADI protocol mechanism to announce, in their core IS-IS
   LSPs, the Data Labels for which they are participating in [ESADI] by
   using the Interested VLANs and/or Interested Labels sub-TLVs
   [RFC6326bis]. This will cause them to be pushed the Directory
   information for all such Data Labels that are being served by one or
   more Push Directory servers.



2.2 Push Directory Servers

   Push Directory servers advertise their availability to push the
   mapping information for a particular Data Label to each other and to
   ESADI participants for that Data Label by turning on a flag bit in
   their ESADI Parameter APPsub-TLV [ESADI] for that ESADI instance (see
   Section 8.1).  Each Push Directory server MUST participate in ESADI
   for the Data Labels for which it will push mappings and set the PD
   (Push Directory) bit in their ESADI-Parameters APPsub-TLV for that
   Data Label.

   For robustness, it is useful to have more than one copy of the data
   being pushed. Each RBridge that is a Push Directory server is
   configured with a number in the range 1 to 8, which defaults to 2,
   for each Data Label for which it can push directory information. If


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   the Push Directories for a Data Label are configured the same in this
   regard and enough such servers are available, this is the number of
   copies of the directory that will be pushed.

   Each Push Directory server also has an 8-bit priority to be Active
   (see Section 8.1 of this document). This priority is treated as an
   unsigned integer where larger magnitude means higher priority and is
   in its ESADI Parameter APPsub-TLV. In cases of equal priority, the
   6-byte IS-IS System ID is used as a tie breaker and treated as an
   unsigned integer where larger magnitude means higher priority.

   For each Data Label it can serve, each Push Directory server orders,
   by priority, the Push Directory servers that it can see in the ESADI
   link state database for that Data Label that are data reachable
   [RFCclear] and determines its position in that order. If a Push
   Directory server is configured to believe that N copies of the
   mappings for a Data Label should be pushed and finds that it is
   number K in the priority ordering (where number 1 is highest priority
   and number K is lowest), then if K is less than or equal to N the
   Push Directory server is Active. If K is greater than N it is
   Passive. Active and Passive behavior are specified below.



2.3 Push Directory Server State Machine

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



2.3.1 Push Directory States

   A Push Directory Server is in one of six states, as listed below, for
   each Data Label it can serve. In addition, it has an internal State-
   Transition-Time variable for each such Data Label which it set at
   each state transition and which enables it to determine how long it
   has been in its current state.

   Down: 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] with the PD bit zero in its ESADI-
      Parameters or might be not participating in [ESADI] at all. (All
      states other than the Down state are considered to be Up states.)

   Passive: No Push Directory data is advertised. Any outstanding EASDI-
      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.


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      The Push Directory participates in [ESADI] and its [ESADI]
      fragment zero includes an ESADI-Parameters APPsub-TLV with the PD
      bit set to one and CP (Complete Push) bit zero.

   Active: If a Push Directory server is Active, it advertises its
      directory data through [ESADI] in its ESADI-LSPs using the
      Interface Addresses [IA] APPsub-TLV and updates that information
      as it changes.  The PD bit is set to one in the ESADI-Parameters
      and the CP bit must be zero.

   Completing: Same behavior as the Active state but responds
      differently to events.

   Complete: The same behavior as Completing except that the CP bit in
      the ESADI-Parameters APPsub-TLV is set to one and the server
      responds differently to events.

   Reducing: The same behavior as Complete but responds differently to
      events. The PD bit remains a one but the CP bit is cleared to zero
      in the ESADI-Parameters APPsub-TLV.  Directory updates continue to
      be advertised.



2.3.2 Push Directory Events and Conditions

   Three auxiliary conditions referenced later in this section are
   defined as follows for convenience:

   The Activate Condition: The server determines that there are K data
      reachable Push Directory servers, the server is configured that
      there should be N copies pushed, and K is less than or equal to N.

   The Pacify Condition: The server determines that there are K data
      reachable Push Directory servers, the server is configured that
      there should be N copies pushed, and K is greater than N.

   The Time Condition: The server has been in its current state for an
      amount of time equal to or larger than its CSNP time (see Section
      8.1).)

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

   1. Push Directory server or TRILL switch was configured to be down
      but the TRILL switch on which it resides is up and the server is
      configured to be up.

   2. The Push Directory server or the TRILL switch on which it is
      resident is being shut down.


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   3. The Activate Condition is met and the server is not configured to
      believe it has complete data.

   4. The server determines that the Pacify Condition is met.

   5. The server is configured to believe it has complete data and the
      Activate Condition is met.

   6. The server is configured to believe it does not have complete
      data.

   7. The Time Condition is met.



2.3.3 State Transition Diagram and Table

   The state transition diagram is as follows.


































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            +-----------+
            | Down      |<---------+
            +-----------+          |
              |1  ^   | 3,4,5,6,7  |
              |   |   +------------+
              V   |2
            +-----------+
            | Passive   |<-----------------------
            +-----------+        ^   ^         ^
              |5   |3  |1,4,6,7  |   |         |
              |    |   +---------+   |         |
              |    V                 |2,4      |
              |  +---------------------+       |
              |  | Active              |<--+   |
              |  +---------------------+   |   |
              |   |5  ^    |1,3,6,7  ^     |   |
              |   |   |    |         |     |   |
              |   |   |    +---------+     |   |
              |   |   |                    |   |
              V   V   |3,6                 |   |
            +--------------+               |   |
            | Completing   |-------------------+
            +--------------+ 2,4           |
              |7  |1,5  ^                  |
              |   |     |                  |
              |   +-----+                  |
              V                            |7
            +-------------+          +----------------+
            | Complete    |--------->| Reducing       |<--+
            +-------------+ 2,3,4,6  +----------------+   |
              |1,5,7 ^  ^              |5  |1,2,3,4,6     |
              |      |  |              |   |              |
              +------+  +--------------+   +--------------+

                    Figure 1. Push Server State Diagram

   This state diagram is equivalent to the following transition table:

      Event || Down  |Passive   |Active  |Completing|Complete|Reducing|
      ------++-------+----------+--------+----------+--------+--------+
         1  ||Passive|Passive   |Active  |Completing|Complete|Reducing|
         2  || Down  | Down     |Passive |Passive   |Reducing|Reducing|
         3  || Down  |Active    |Active  |Active    |Reducing|Reducing|
         4  || Down  |Passive   |Passive |Passive   |Reducing|Reducing|
         5  || Down  |Completing|Complete|Completing|Complete|Complete|
         6  || Down  |Passive   |Active  |Active    |Reducing|Reducing|
         7  || Down  |Passive   |Active  |Complete  |Complete|Active  |





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2.4 Additional Push Details

   Push Directory mappings can be distinguished for any other data
   distributed through ESADI because mappings are distributed only with
   the Interface Addresses APPsub-TLV [IA] and are flagged as being Push
   Directory data.

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

   Because a Push Directory server may need to advertise interest in
   Data Labels even if it does not want to receive end station data in
   those Data Labels, the No Data flag bit is provided as discussed in
   Section 6.3.

   If an RBridge notices that a Push Directory server is no longer data
   reachable [RFCclear], it 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 impractical for an RBridge receiving Push Directory information
   to ever be absolutely certain that it has complete information.
   However, it can obtain a reasonable assurance of complete information
   by requiring two conditions to be met:
      1. The PD and CP bits are on in the ESADI zero fragment from the
         server for the relevant Data Label.
      2. A client RBridge might be just coming up and receive an EASDI
         LSP meeting the requirement in point 1 above but have not yet
         received all of the ESADI LSP fragment from the Push Directory
         server. Thus, it should not believe that information to be
         complete unless it has also had data connectivity to the server
         for the larger of the client's and the server's CSNP times.

   There may be transient conflicts between mapping information from
   different Push Directory servers or conflicts between locally learned
   information and information received from a Push Directory server. In
   case of such conflicts, information with a higher confidence value is
   preferred over information with a lower confidence. In case of equal
   confidence, 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.



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2.5 Primary to Secondary Server Push Service

   A secondary Push or Pull Directory server is one that obtains its
   data from a primary directory server. 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 Push Directory server takes the pushed data it receives
   from the highest priority Push Directory server and re-originates it.












































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3. Pull Model Directory Assistance Mechanisms

   In the Pull Model, a TRILL switch (RBridge) pulls directory
   information from an appropriate Directory Server when needed.

   Pull Directory servers for a particular Data Label X are located by
   looking in the core TRILL IS-IS link state database for RBridges that
   advertise themselves by having the Pull Directory flag on in their
   Interested VLANs or Interested Labels sub-TLV [RFC6326bis] for X. If
   multiple RBridges indicate that they are Pull Directory Servers for a
   particular Data Label, pull requests can be sent to any one or more
   of them that are data reachable but it is RECOMMENDED that pull
   requests be preferentially sent to the server or servers that are
   lower cost from the requesting RBridge.

   Pull Directory requests are sent by enclosing them in an RBridge
   Channel [Channel] message using the Pull Directory channel protocol
   number (see Section 8.2).  Responses are returned in an RBridge
   Channel message using the same channel protocol number.

   The requests to Pull Directory Servers are typically derived from
   normal ARP [RFC826], ND [RFC4861], RARP [RFC903] messages or data
   frames with unknown unicast destination MAC addresses intercepted by
   the RBridge as described in Section 4.

   Pull Directory responses include an amount of time for which the
   response should be considered valid. This includes negative responses
   that indicate no data is available. Thus both positive responses with
   data and negative responses can be cached and used for immediate
   response to ARP, ND, RARP, or unknown destination MAC frames, until
   they expire.  If information previously pulled is about to expire, an
   RBridge MAY try to refresh it by issued a new pull request but, to
   avoid unnecessary requests, SHOULD NOT do so if it has not been
   recently used.



3.1 Pull Directory Request Format

   A Pull Directory request is sent as the Channel Protocol specific
   content of an inter-RBridge Channel message [Channel] TRILL Data
   packet. The Data Label in the packet is the Data Label in which the
   query is being made. The priority of the channel message is a mapping
   of the priority of the frame being ingressed that caused the request
   with the default mapping depending, per Data Label, on the strategy
   (see Section 6). The Channel Protocol specific data is formatted as
   follows:





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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   V   | T |   RESV    | Count |              RESV             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence Number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | QUERY 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | QUERY 2
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | QUERY K
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...

      V: Version of the Pull Directory protocol as an unsigned integer.
         Version zero is specified in this document.

      T: Type. 0 => Response, 1=> Query, 2=> Unsolicited Update, 3=>
         Reserved. An unsolicited update is formatted as a response
         except there is no corresponding query. Messages received with
         type = 3 are discarded. Queries received by an RBridge that is
         not a Pull Directory are discarded. Responses that do not match
         an outstanding Query are discarded.

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

      Count: Number of queries present.

      Sequence Number: A 32-bit quantity set by the sending RBridge,
         returned in any responses, and used to match up responses with
         queries.  It is opaque except that the value zero is reserved
         for Unsolicited Update response messages. A Request received
         with Sequence Number zero is discarded.

      QUERY: Each Query record within a Pull Directory request message
         is formatted as follows:














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             0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
           +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
           |        SIZE           |    RESV   |   TYPE    |
           +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
         If TYPE = 1
           +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
           |                      AFN                      |
           +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
           |  Query address ...
           +--+--+--+--+--+--+--+--+--+--+--...
         If TYPE = 2, 3, 4, or 5
           +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
           |  Query frame ...
           +--+--+--+--+--+--+--+--+--+--+--...

         SIZE: Size of the query data in bytes as an unsigned byte
            starting with and including the SIZE field itself. Thus the
            minimum legal value is 2. A value of SIZE less than 2
            indicates a malformed message. The "QUERY" with the illegal
            SIZE value and all subsequent QUERYs MUST be ignored and the
            entire query message MAY be ignored.

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

         TYPE: There are two types of queries currently defined, (1) a
            query that provides an explicit address and asks for other
            addresses for the interface specified by the query address
            and (2) a query that includes a frame. The fields of each
            are specified below. Values of TYPE are as follows

                  TYPE   Description
                  ----   -----------
                     0    reserved
                     1    query address
                     2    ARP query frame
                     3    ND query frame
                     4    RARP query frame
                     5    Unknown unicast MAC query frame
                  6-14    assignable by IETF Review
                    15    reserved

            AFN: Address Family Number of the query address.

            Query Address: The query is asking for any other addresses,
               and the RBridge from which they are reachable, that
               correspond to the same interface, within the data label
               of the query. Typically that would be either (1) a MAC
               address with the querying RBridge primarily interested in
               the RBridge by which that MAC address is reachable, or


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               (2) an IP address with the querying RBridge interested in
               the corresponding MAC address and the RBridge by which
               that MAC address is reachable. But it could be some other
               address type.

            Query Frame: Where a Pull Directory query is the result of
               an ARP, ND, RARP, or unknown unicast MAC destination
               address, the ingress RBridge MAY send the frame to a Pull
               Directory Server if the frame is small enough to fit into
               a query message.

   A query count of zero is explicitly allowed, for the purpose of
   pinging a Pull Directory server to see if it is responding to
   requests. On receipt of such an empty query message, a response
   message that also has a count of zero MUST be sent unless inhibited
   by rate limiting.

   If no response is received to a Pull Directory request within a
   timeout configurable in milliseconds that defaults to 2,000, the
   request should be re-transmitted with the same Sequence Number up to
   a configurable number of times that defaults to three. If there are
   multiple queries in a request, responses can be received to various
   subsets of these queries by the timeout. In that case, the remaining
   unanswered queries should be re-sent in a new query with a new
   sequence number.  If an RBridge is not capable of handling partial
   responses to requests with multiple queries, it MUST NOT sent a
   request with more than one query in it.



3.2 Pull Directory Response Format

   Pull Directory responses are sent as the Channel Protocol specific
   content of inter-RBridge Channel message TRILL Data packets.
   Responses are sent with the same Data Label and priority as the
   request to which they correspond except that the response priority is
   limited to be not more than a configured value. This priority limit
   is configurable at a per RBridge level and defaults to priority 6.
   The Channel protocol specific data format is as follows:













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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   V   | T |F|P|N| RESV| Count |      ERR      |  subERR       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence Number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | RESPONSE 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | RESPONSE 2
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | RESPONSE K
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...

      V, T: Version and Type as specified in Section 3.1.

      F: The Flood bit. If zero, the reply is to be unicast to the
         provided Nickname. If T=2, F=1 is used to flood messages for
         certain unsolicited update cache consistency maintenance
         messages from an end station Pull Directory server as discussed
         in Section 3.5. If T is not 2, F is ignored.

         P, N: Flags used in connection with certain flooded unsolicited
         cache consistency maintenance messages. Ignored if T is not 2.
         If the P bit is a one, the solicited response message relates
         to cached positive response information. If the N bit is a one,
         the unsolicited message relates to cached negative information.
         See Section 3.5.

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

      Count: Count is the number of responses present in the particular
         response message.

      ERR, subERR: A two part error code. See Section 3.4.

      Sequence Number: A 32-bit quantity set by the sending RBridge,
         returned in any responses, and used to match up responses with
         queries. It is opaque except that the value zero is reserved
         for Unsolicited Update response messages.

      RESPONSE: Each response record within a Pull Directory response
         message is formatted as follows:







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

         SIZE: Size of the response data in bytes starting with and
            including the SIZE field itself. Thus the minimum value of
            SIZE is 6. If SIZE is less than 6, that RESPONSE and all
            subsequent RESPONSEs MUST be ignored.

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

         Index: The relative index of the query in the request message
            to which this response corresponds. The index will always be
            one for request messages containing a single query. The
            index will always be zero for unsolicited update "response"
            messages.

         Lifetime: The length of time for which the response should be
            considered valid in seconds. If zero, the response can only
            be used for the particular query from which it resulted. The
            maximum time that can be expressed is just over 18.2 hours.
            [Perhaps this should be in units of, say, 200 milliseconds?]

         Response Data: There are two types of response data.
            If the ERR field is non-zero, the response data is a copy of
               the query data, that is, either an AFN followed by an
               address or a query frame.
            If the ERR field is zero, the response data is the contents
               of an Interface Addresses APPsub-TLV (see Section 5)
               without the usual TRILL GENINFO TLV type and length and
               without the usual IA APPsub-TLV type and length before
               it. The maximum size of such contents is 251 bytes in the
               case when SIZE is 255.

   Multiple response records can appear in a response message with the
   same index if the answer to a query consists of multiple Interface
   Address APPsub-TLV contents. This would be necessary if, for example,
   a MAC address within a Data Label appears to be reachable by multiple
   RBridges. 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 to include by some method outside
   the scope of this document.



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   See Section 3.4 for a discussion of how errors are handled.



3.3 Pull Directory Hosted on an End Station

   Optionally, a Pull Directory actually hosted on an end station MAY be
   supported. In that case, when the RBridge advertising itself as a
   Pull Directory server receives a query, it modifies the inter-RBridge
   Channel message received into a native RBridge Channel message and
   forwards it to that end station. Later, when it receives one or more
   responses from that end station by native RBridge Channel messages,
   it modifies them into inter-RBridge Channel messages and forwards
   them to the source RBridge of the query.

   The native Pull Directory RBridge Channel messages use the same
   Channel protocol number as do the inter-RBridge Pull Directory
   RBridge Channel messages. The native messages MUST be sent with an
   Outer.VLAN tag which gives the priority of each message which is the
   priority of the original inter-RBridge request packet. The Outer.VLAN
   ID used is the Designated VLAN on the link.

   The native RBridge Channel message protocol dependent data for a Pull
   Directory query is formatted as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   V   | T |   RESV    | Count |           Nickname            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Data Label ... (4 or 8 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence Number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | QUERY 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | QUERY 2
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | QUERY K
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...

      Data Label: The Data Label of the original inter-RBridge Pull
         Directory Channel protocol messages that was mapped to this
         native channel message. The format is the same as it appears
         right after the Inner.MacSA of the original Channel message.

      Nickname: The nickname of the RBridge sending the original inter-
         RBridge Pull Directory query.


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      All other fields, including the fields within the QUERY records
         are as specified in Section 3.1.

   The native RBridge Channel message protocol specific content for a
   Pull Directory response is formatted as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   V   | T |F|P|N| RESV| Count |      ERR      |  subERR       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Nickname            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Data Label ... (4 or 8 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Sequence Number                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | RESPONSE 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | RESPONSE 2
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      | RESPONSE K
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...

      Nickname: If F=0, the nickname of the ultimate destination
         RBridge. If F=1, ignored.

      Data Label: The Data Label to which the response applies. The
         format is the same as it appears right after the Inner.MacSA in
         TRILL Data messages.

      All other fields, including the fields within the RESPONSE
         records, are as specified in Section 3.2.



3.4 Pull Directory Request Errors

   An error response message is indicated by a non-zero ERR field.

   If there is an error that applies to an entire request message or its
   header, as indicated by the range of the value of the ERR field, then
   the query records in the request are just echoed back in the response
   records but expanded with a zero Lifetime and the insertion of the
   Index field.

   If errors occur at the query level, they MUST be reported in a
   response message separate from the results of any successful queries.


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   If multiple queries in a request have different errors, they MUST be
   reported in separate response messages. If multiple queries in a
   request have the same error, this error response MAY be reported in
   one response message.

   In an error response message, the query or queries being responded to
   appear, expanded by the Lifetime for which the server thinks the
   error might persist and with their Index inserted, as the RESPONSE
   record.

   ERR values 1 through 127 are available for encoding request message
   level errors. ERR values 128 through 254 are available for encoding
   query level errors. 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.

       ERR     Meaning
       ---     -------
         0     (no error)

         1     Unknown or reserved field value
         2     Request data too short
      3-127    (Available for allocation by IETF Review)

       128     Unknown AFN
       129     Address not found
      130-254  (Available for allocation by IETF REview)
       255     Reserved

   The following sub-errors are specified under error code 1:

      SubERR   Field with Error
      ------   ----------------
         0     Unspecified
         1     Unknown V field value
         2     Reserved T field value
         3     Zero sequence number in request
      4-254    (Available for allocation by IETF Review)
       255     Reserved

   More TBD



3.5 Cache Consistency

   Pull Directories MUST take action to minimize the amount of time that
   an RBridge will continue to use stale information from the Pull
   Directory.



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   A Pull Directory server MUST maintain one of the following, in order
   of increasing specificity. Retaining more specific records, such as
   that given in item 3 below, minimizes spontaneous response messages
   sent to update pull client RBridge caches. Retaining less specific
   records, such as that given in item 1, will generally increase the
   volume and overhead due to spontaneous response messages but still
   maintain consistency.

      1. An overall record per Data Label of when the last positive
         response data will expire at a requester and when the last
         negative response will expire.

      2. For each unit of data (IA APPsub-TLV Address Set [IA]) held by
         the server and each address about which a negative response was
         sent, when the last expected response with that data or
         negative response will expire at a requester.

      3. For each unit of data held by the server and each address about
         which a negative response was sent, a list of RBridges that
         were sent that data as the response or sent a negative response
         for the address, with the expected time to expiration at each
         of them.

   A Pull Directory server may have a limit as to how many RBridges it
   can maintain expiry information for by method 3 above or how many
   data units or addresses it can maintain expiry information for by
   method 2. If such limits are exceeded, it MUST transition to a lower
   numbered strategy but, in all cases, MUST support, at a minimum,
   method 1.

   When data at a Pull Directory changes or is deleted or data is added
   and there may be unexpired stale information at a requesting RBridge,
   the Pull Directory MUST send an unsolicited message as discussed
   below.

   If method 1, the most crude 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 message is flooded (multicast) within that
   Data Label. And if data is added and there are outstanding cached
   negative responses, an all-addresses flush negative message is
   flooded. "All-addresses" is indicated by the Count in an unsolicited
   response being zero. On receiving an all-addresses flooded flush
   positive message from a Pull Directory server it has used, indicated
   by the U, F, and P bits being one, an RBridge discards all cached
   data responses it has for that Data Label. Similarly, on receiving an
   all addresses flush negative message, indicated by the U, F, and N
   bits being one, it discards all cached negative responses for that
   Data Label. A combined flush positive and negative can be flooded by
   having all of the U, F, P, and N bits set to one resulting in the


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   discard of all positive and negative cached information for the Data
   Label.

   If method 2 is being followed, then an RBridge floods address
   specific unsolicited update positive responses when data which is
   cached by a querying RBridge is changed or deleted and floods an
   address specific unsolicited update negative response when such
   information is added to. Such messages are similar to the method 1
   flooded unsolicited flush messages. The U and F bits will be one and
   the message will be multicast. However that Count field will be non-
   zero and either the P or N bit, but not both, will be one. On
   receiving such as address specific message, if it is positive the
   addresses in the response records in the unsolicited response are
   compared to the addresses about which the recipient RBridge is
   holding cached positive or negative information and, if they match,
   the cached information is updated or the negative information
   replaced with the new positive information. On receiving an address
   specific unsolicited update negative response, the addresses in the
   response records in the unsolicited response are compared to the
   addresses about which the recipient RBridge is holding cached
   positive or negative information and, if they match, the any cached
   positive information is discarded.

   If method 3 is being followed, the same sort of unsolicited update
   messages are sent as with method 2 except they are not normally
   flooded but unicast only to the specific RBridges the server believes
   may be holding the cached positive or negative information that may
   need updating. However, the Pull Directory server MAY flood the
   unsolicited update, for example if it determines that a sufficiently
   large fraction of its requesters need to be updated.



3.6 Additional Pull Details

   If an RBridge notices that a Pull Directory server is no longer data
   reachable [RFCclear], it MUST discard all pull responses it is
   retaining from that server as the RBridge can no longer receive cache
   consistency messages from the server.

   Because a Pull Directory server may need to advertise interest in
   Data Labels even though it does not want to received end station data
   in those Data Labels, the No Data flag bit is provided as specified
   in Section 8.3.








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4. Events That May Cause Directory Use

   An RBridge 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) by requesting information from a
   Pull Directory. However, the following are expected to be the most
   common circumstances leading to directory information use. All of
   these are cases of ingressing (or originating) a native frame.

   Support for each of the uses below is separately optional.



4.1 Forged Native Frame Ingress

   End stations can forge the source MAC and/or IP address in a native
   frame that an edge TRILL switch receives for ingress in some
   particular Data Label. If there is complete Directory information as
   to what end stations should be reachable by an egress TRILL switch or
   a port on such a TRILL switch, frames with forged source addresses
   SHOULD be discarded.  If such frames are discarded, then none of the
   special processing in the remaining subsection of this Section 2
   occur and MAC address learning (see [RFC6325] Section 4.8) SHOULD NOT
   occur. ("SHOULD NOT" is chosen because it is harmless in cases where
   it has no effect. For example, if complete directory information is
   available and such directory information is treated as having a
   higher confidence that MAC addresses learned from the data plane.)



4.2 Unknown Destination MAC

   Ingressing a native frame with an unknown unicast destination MAC:
      The mapping from the destination MAC and Data Label to the egress
      TRILL switch from which it is reachable is needed to ingress the
      frame as unicast. If the egress RBridge is unknown, the frame must
      be either dropped or ingressed as a multi-destination frame which
      is flooded to all edge RBridges for its Data Label resulting in
      increased link utilization compared with unicast routing.
      Depending on the configuration of the TRILL switch ingressing the
      native frame (see Section 6), directory information can be used
      for the { destination MAC, Data Label } to egress TRILL switch
      nickname mapping and destination MACs for which such direction
      information is not available MAY be discarded.








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4.3 Address Resolution Protocol (ARP)

   Ingressing an ARP [RFC826]:

      ARP is a flexible protocol. It is commonly used on a link to query
      for the MAC address corresponding to an IPv4 address, test if an
      IPv4 address is in use, or to announce a change in any of IPv4
      address, MAC address, and/or point of attachment.

      The logically important elements in an ARP are (1) the
      specification of a "protocol" and a "hardware" address type, (2)
      an operation code that can be Request or Reply, and (3) fields for
      the protocol and hardware address of the sender and the target
      (destination) node.

   Examining the three types of ARP use:

   1. General ARP Request / Response
      This is a request for the destination "hardware" address
      corresponding to the destination "protocol" address; however, if
      the source and destination protocol addresses are equal, it should
      be handled as in type 2 below. A general ARP is handled by doing a
      directory lookup on the destination "protocol" address provided in
      hops of finding a mapping to the desired "hardware" address. If
      such information is obtain from a directory, a response can be
      synthesized.

   2. Gratuitous ARP
      A request used by a host to announce a new IPv4 address, new MAC
      address, and/or new point of network attachment. Identifiable
      because the sender and destination "protocol" address fields have
      the same value. Thus, under normal circumstances, there really
      isn't any separate destination host to generate a response. If
      complete Push Directory information is being used with the Notify
      flag set in the IA APPsub-TLVs being pushed [IA] by all the
      RBridge in the Data Label, then gratuitous ARPs SHOULD be
      discarded rather the ingressed.  Otherwise, they are either
      ingressed and flooded or discarded depending on local policy.

   3. Address Probe ARP Query
      An address probe ARP is used to determine if an IPv4 address is in
      use [RFC5227].  It can be identified by the source "protocol"
      (IPv4) address field being zero.  The destination "protocol"
      address field is the IPv4 address being tested.  If some host
      believes it has that destination IPv4 address, it would respond to
      the ARP query, which indicates that the address is in use.
      Address probe ARPs can be handled the same as General ARP queries.





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4.4 IPv6 Neighbor Discovery (ND)

   Ingressing an IPv6 ND [RFC4861]:
      TBD

      Secure Neighbor Discovery messages [RFC3971] will, in general,
      have to be sent to the neighbor intended so that neighbor can sign
      the answer; however, directory information can be used to unicast
      a Secure Neighbor Discovery packet rather than multicasting it.



4.5 Reverse Address Resolution Protocol (RARP)

   Ingressing a RARP [RFC903]:
      RARP uses the same packet format as ARP but different Ethertype
      and opcode values. Its use is similar to the General ARP
      Request/Response as described above.  The difference is that it is
      intended to query for the destination "protocol" address
      corresponding to the destination "hardware" address provided.  It
      is handled by doing a directory lookup on the destination
      "hardware" address provided in hops of finding a mapping to the
      desired "protocol" address. For example, looking up a MAC address
      to find the corresponding IP address.




























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5. Layer 3 Address Learning

   TRILL switches MAY learn IP addresses in a manner similar to that in
   which they learn MAC addresses. On ingress of a native IP frame, they
   can learn the { IP address, MAC address, Data Label, input port } set
   and on the egress of a native IP frame, they can learn the { IP
   address, MAC address, Data Label, remote RBridge } information plus
   the nickname of the RBridge that ingressed the frame.

   This locally learned information is retained and times out in a
   similar manner to MAC address learning specified in [RFC6325]. By
   default, it has the same Confidence as locally learned MAC
   reachability information.

   Such learned Layer 3 address information MAY be disseminated with
   [ESADI] using the IA APPsub-TLV [IA]. It can also be used as, in
   effect, local directory information to assist in locally responding
   to ARP/ND packets as discussed in Section 4.


































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6. Directory Use Strategies and Push-Pull Hybrids

   For some edge nodes which have a great number of Data Labels enabled,
   managing the MAC and Data Label <-> EdgeRBridge 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 a
   majority of Data Labels if not all.

   For those RBridge Edge nodes, a hybrid model should be considered.
   That is the Push Model is used for some Data Labels, and the Pull
   Model is used for other Data Labels. It is the network operator's
   decision by configuration as to which Data Labels' mapping entries
   are pushed down from directories and which Data Labels' mapping
   entries are pulled.

   For example, assume a data center when hosts in specific Data Labels,
   say VLANs 1 through 100, communicate regularly with external peers,
   the mapping entries for those 100 VLANs should be pushed down to the
   data center gateway routers. For hosts in other Data Labels which
   only communicate with external peers occasionally for management
   interface, the mapping entries for those VLANs should be pulled down
   from directory when the need comes up.

   The mechanisms described above for Push and Pull Directory services
   make it easy to use Push for some Data Labels and Pull for others. In
   fact, different RBridges 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. And there can be Data Labels for which directory
   services are not used at all.

   For Data Labels in which a hybrid push/pull approach is being taken,
   it would make sense to use push for address information of hosts that
   frequently communicate with many other hosts in the Data Label, such
   as a file or DNS server. Pull could then be used for hosts that
   communicate with few other hosts, perhaps such as hosts being used as
   compute engines.



6.1 Strategy Configuration

   Each RBridge that has the ability to use directory assistance has,
   for each Data Label X in which it is might ingress native frames, one
   of four major modes:

      0. No directory use. The RBridge does not subscribe to Push
         Directory data or make Pull Directory requests for Data Label X
         and directory data is not consulted on ingressed frames in Data
         Label X that might have used directory data. This includes ARP,


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         ND, RARP, and unknown MAC destination addresses, which are
         flooded.

      1. Use Push only. The RBridge subscribes to Push Directory data
         for Data Label X.

      2. Use Pull only. When the RBridge ingresses a frame in Data Label
         X that can use Directory information, if it has cached
         information for the address it uses it. If it does not have
         either cached positive or negative information for the address,
         it sends a Pull Directory query.

      3. Use Push and Pull. The RBridge subscribes to Push Directory
         data for Data Label X. When it ingresses a frame in Data Label
         X that can use Directory information and it does not find that
         information in its link state database of Push Directory
         information, it makes a Pull Directory query.

   The above major Directory use mode is per Data Label. In addition,
   there is a per Data Label per priority minor mode as listed below
   that indicates what should be done if Directory Data is not available
   for the ingressed frame. In all cases, if you are holding Push
   Directory or Pull Directory information to handle the frame given the
   major mode, the directory information is simply used and, in that
   instance, the minor modes does not matter.

      A. Flood immediate. Flood the frame immediately (even if you are
         also sending a Pull Directory) request.

      B. Flood. Flood the frame immediately unless you are going to do a
         Pull Directory request, in which case you wait for the response
         or for the request to time out after retries and flood the
         frame if the request times out.

      C. Discard if complete or Flood immediate. If you have complete
         Push Directory information and the address is not in that
         information, discard the frame. If you do not have complete
         Push Directory information, the same as A above.

      D. Discard if complete or Flood. If you have complete Push
         Directory information and the address is not in that
         information, discard the frame. If you do not have complete
         Push Directory information, the same as B above.

   In addition, the query message priority for Pull Directory requests
   sent can be configured on a per Data Label, per ingressed frame
   priority basis.  The default mappings are as follows where Ingress
   Priority is the priority of the native frame that provoked the Pull
   Directory query:



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         Ingress     If Flood    If Flood
         Priority    Immediate   Delayed
         --------    ---------   --------
           7           5           6
           6           5           6
           5           4           5
           4           3           4
           3           2           3
           2           0           2
           0           1           0
           1           1           1

   Priority 7 is normally only used for urgent messages critical to
   adjacency and so is avoided by default for directory traffic.






































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7. Security Considerations

   Push Directory data is distributed through ESADI-LSPs [ESADI] which
   can be authenticated with the same mechanisms as IS-IS LSPs. See
   [RFC5304] [RFC5310] and the Security Considerations section of
   [ESADI].

   Pull Directory queries and responses are transmitted as RBridge-to-
   RBridge or native RBridge Channel messages. Such messages can be
   secured as specified in [ChannelTunnel].

   For general TRILL security considerations, see [RFC6325].








































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8. IANA Considerations

   This section give IANA allocation and registry considerations.



8.1 ESADI-Parameter Data

   IANA is request to allocate two ESADI-Parameter TRILL APPsub-TLV flag
   bits for "Push Directory" (PD) and "Complete Push" (CP) and to create
   a sub-registry in the TRILL Parameters Registry as follows:

      Sub-Registry: ESADI-Parameter APPsub-TLV Flag Bits

      Registration Procedures: Expert Review

      References: [ESADI], This document

         Bit  Mnemonic  Description                      Reference
         ---  --------  -----------                      ---------
          0      UN     Supports Unicast ESADI           [ESADI]
          1      PD     Push Directory Server            This document
          2      CP     Complete Push                    This document
         3-7     -      available for allocation

   The CP bit is ignored if the PD bit is zero.

   In addition, the ESADI-Parameter APPsub-TLV is optionally extended,
   as provided in its original specification in [ESADI], by one byte as
   show below:

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

   The meanings of all the fields are as specified in [ESADI] 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


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   the PushDirPriority field is not present (Length = 3) it is treated
   as if it were 0x40. 0x40 is also the value used and placed here by an
   RBridge priority to be a Push Directory has not been configured.



8.2 RBridge Channel Protocol Number

   IANA is requested to allocate a new RBridge Channel protocol number
   for "Pull Directory Services" from the range allocable by Standards
   Action and update the table of such protocol number in the TRILL
   Parameters Registry referencing this document.



8.3 The Pull Directory and No Data Bits

   IANA is requested to allocate two currently reserved bits in the
   Interested VLANs field of the Interested VLANs sub-TLV (suggested
   bits 18 and 19) and the Interested Labels field of the Interested
   Labels sub-TLV (suggested bits 6 and 7) [RFC6326bis] to indicate Pull
   Directory server (PD) and No Data (ND) respectively. These bits are
   to be added to the subregistry created by [ESADI] with this document
   as reference.

   In the TRILL base protocol [RFC6325] as extended for FGL [rfcFGL],
   the mere presence of an Interested VLANs or Interested Labels sub-
   TLVs in the LSP of an RBridge indicates connection to end stations in
   the VLANs or FGLs listed and thus a desire to receive multi-
   destination traffic in those Data Labels. But, with Push and Pull
   Directories, advertising that you are a directory server requires
   using these sub-TLVs for the Data Label you are serving. If such a
   directory server does not wish to received multi-destination TRILL
   Data packets for the Data Labels it lists in one of these sub-TLVs,
   it sets the "No Data" (ND) bit to one. This means that data on a
   distribution tree may be pruned so as not to reach the "No Data"
   RBridge as long as there are no RBridges interested in the Data who
   are beyond the "No Data" RBridge.  This bit is backwards compatible
   as RBridges ignorant of it will simply not prune when they could,
   which is safe although it may cause increased link utilization.

   An example of as RBridge serving as a directory that would not want
   multi-destination traffic in some Data Labels might be an RBridge
   that does not officer end station service for any of the Data Labels
   for which it is serving as a directory and is either (1) a Pull
   Directory or (2) a Push Directory for which all of the ESADI traffic
   can be handled by unicast [ESADI].





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INTERNET-DRAFT                        TRILL: Directory Assist Mechanisms


Acknowledgments

   The contributions of the following persons are gratefully
   acknowledged:

        TBD

   The document was prepared in raw nroff. All macros used were defined
   within the source file.



Normative References

   [RFC826] - Plummer, D., "An Ethernet Address Resolution Protocol",
         RFC 826, November 1982.

   [RFC903] - Finlayson, R., Mann, T., Mogul, J., and M. Theimer, "A
         Reverse Address Resolution Protocol", STD 38, RFC 903, June
         1984

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

   [RFC3971] - Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
         "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC4861] - Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
         "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
         September 2007.

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

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

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

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

   [RFC5342bis] - Eastlake 3rd, D., "IANA Considerations and IETF
         Protocol Usage for IEEE 802 Parameters", BCP 141, RFC 5342,
         September 2008.

   [RFC6326bis] - Eastlake, D., Banerjee, A., Dutt, D., Perlman, R., and


L. Dunbar, et al                                               [Page 33]

INTERNET-DRAFT                        TRILL: Directory Assist Mechanisms


         A. Ghanwani, "TRILL Use of IS-IS", draft-ietf-isis-rfc6326bis,
         work in progress.

   [RFCclear] - Eastlake, D., M. Zhang, A. Ghanwani, V. Manral, A.
         Banerjee, draft-ietf-trill-clear-correct-06.txt, in RFC
         Editor's queue.

   [Channel] - D. Eastlake, V. Manral, Y. Li, S. Aldrin, D. Ward,
         "TRILL: RBridge Channel Support", draft-ietf-trill-rbridge-
         channel-08.txt, in RFC Editor's queue.

   [RFCfgl] - D. Eastlake, M. Zhang, P. Agarwal, R. Perlman, D. Dutt,
         "TRILL: Fine-Grained Labeling", draft-ietf-trill-fine-
         labeling-07.txt, in RFC Editor's queue.

   [ESADI] - Zhai, H., F. Hu, R. Perlman, D. Eastlake, O. Stokes, "TRILL
         (Transparent Interconnection of Lots of Links): The ESADI (End
         Station Address Distribution Information) Protocol",
         draft-ietf-trill-esadi, work in progress.

   [IA] - Eastlake, D., L. Yizhou, R. Perlman, "TRILL: Interface
         Addresses APPsub-TLV", draft-eastlake-trill-ia-appsubtlv, work
         in progress.



Informational References

   [RFC5227] - Cheshire, S., "IPv4 Address Conflict Detection", RFC
         5227, July 2008.

   [DirectoryFramework] - Dunbar, L., D. Eastlake, R. Perlman, I.
         Gashinsky, "TRILL Edge Directory Assistance Framework",
         draft-ietf-trill-directory-framework, in RFC Editor's queue.

   [ChannelTunnel] - D. Eastlake, Y. Li, "TRILL: RBridge Channel Tunnel
         Protocol", draft-eastlake-trill-channel-tunnel, work in
         progress.

   [ARP reduction] - Shah, et. al., "ARP Broadcast Reduction for Large
         Data Centers", Oct 2010.











L. Dunbar, et al                                               [Page 34]

INTERNET-DRAFT                        TRILL: Directory Assist Mechanisms


Authors' Addresses

   Linda Dunbar
   Huawei Technologies
   5430 Legacy Drive, Suite #175
   Plano, TX 75024, USA

   Phone: (469) 277 5840
   Email: ldunbar@huawei.com


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

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


   Radia Perlman
   Intel Labs
   2200 Mission College Blvd.
   Santa Clara, CA 95054-1549 USA

   Phone: +1-408-765-8080
   Email: Radia@alum.mit.edu


   Igor Gashinsky
   Yahoo
   45 West 18th Street 6th floor
   New York, NY 10011

   Email: igor@yahoo-inc.com


   Yizhou Li
   Huawei Technologies
   101 Software Avenue,
   Nanjing 210012 China

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








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INTERNET-DRAFT                        TRILL: Directory Assist Mechanisms


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