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TRILL working group                                         L. Dunbar
Internet Draft                                            D. Eastlake
Intended status: Standard Track                                Huawei
Expires: Sept 2012                                       Radia Perlman
                                                          I. Gashinsky
                                                         March 5, 2012

                Mechanisms for Directory Assisting RBridge

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   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.


   This draft describes the mechanisms of using directory server(s) to
   assist RBridge edge in data center environment.

Conventions used in this document

   The term ''Subnet'' and ''VLAN'' are used interchangeably in this
   document because it is common to map one subnet to one VLAN. The
   term ''TRILL'' and ''RBridge'' are used interchangeably in this

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 0.

Table of Contents

   1. Introduction ................................................ 2
   2. Terminology ................................................. 3
   3. Push Model of Directory Assisted RBridge Edge in DC Environment3
      3.1. Minimize the mapping entries maintained by RBridge Edge                                                                      .. 4
      3.2. Aggregated entries to push down ......................... 4
      3.3. Messages to trigger pushing from directory .............. 5
   4. Pull model of Directory Assisted RBridge Edge in DC Environment5
   5. Push-Pull Hybrid Model ....................................... 7
   6. To be continued ............................................. 7
   7. Manageability Considerations................................. 7
   8. Security Considerations...................................... 7
   9. IANA Considerations ......................................... 8
   10. Acknowledgments ............................................ 8
   11. References ................................................. 8
   Authors' Addresses ............................................. 9
   Intellectual Property Statemen ................................. 9
   Disclaimer of Validity ........................................ 10

1. Introduction

   [Directory-Assisted-RBridge] describes the framework of using
   directory to assist TRILL edge nodes to improve TRILL network

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   scalability in data center environment. This draft describes
   mechanisms of using directory to assist RBridge edge nodes in data
   center environment.

2. Terminology

   AF      Appointed Forwarder RBridge port

   Bridge:  IEEE 802.1Q compliant device. In this draft, Bridge is used
             interchangeably with Layer 2 switch.

   DA:     Destination Address

   DC:      Data Center

   EoR:    End of Row switches in data center. Also known as
             Aggregation switches in some data centers

   FDB:    Filtering Database for Bridge or Layer 2 switch

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

   SA:     Source Address

   STP:    Spanning Tree Protocol

   RSTP:    Rapid Spanning Tree Protocol

   ToR:    Top of Rack Switch in data center. It is also known as
             access switches in some data centers.

   VM:     Virtual Machines

3. Push Model of Directory Assisted RBridge Edge in DC Environment

   Under this model, Directory Server(s) push down the MAC&VLAN <->
   RBridgeEdge mapping for all the hosts which might communicate with
   hosts attached to an RBridge edge node. With this environment, it is
   recommended that RBridge edge simply drop a data packet (instead of
   flooding to RBridge domain) if the packet's destination address
   can't be found in the MAC&VLAN<->RBridgeEdge mapping table.

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   The mapping entry to be pushed down could leverage the gratuitous
   ARP reply with extended fields showing the edge RBridge's name, as
   shown in Table 2.

   3.1. Minimize the mapping entries maintained by RBridge Edge

     One major drawback of the ''Push Model'' is that RBridge edge's
     MAC&VLAN<->RBridgeEdge mapping table will have more entries than
     it really needs.

     One simple step for an RBridge to reduce the number of mapping
     entries pushed down from directory is to prune out entries
     belonging to VIDs which are not enabled on its bridged LANs ports.
     For example, if only {vid#1, vid#2, vid#3} are enabled on bridged
     LANs connected to an RBridge edge ports, only MAC&VLAN<-
     >RBridgeEdge entries for those three VIDs need to be pushed down
     to the RBridge edge.

     However, under the situations when hosts/VMs attached to one
     RBridge edge rarely communicate with hosts under the same VLAN
     attached to different RBridge, the normal process of RBridge
     edge's cache aging would have removed those MAC&VLAN entries from
     the RBridge's cache. But it can be difficult for Directory Servers
     to predict the communication patterns among hosts within one VLAN.

     Therefore, even with VLAN pruning, it is likely that the Directory
     Servers will push down more the MAC&VLAN entries to RBridge Edges
     than the normal cache aging approach.

   3.2. Aggregated entries to push down

     Using Table 2 requires one entry per host/VM. When directory
     pushes down the entire mapping to an edge RBridge for the very
     first time, there usually are many entries. To minimize the amount
     of data pushed down, summarization should be considered, e.g. with
     one edge RBridge Nickname being associated with all attached
     hosts' MAC addresses and VLANs as shown below:

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          | Nickname1  |VID-1  | MAC1, MAC2,  MACn              |
          |            |------ +--------------------------------+
          |            |VID-2  | MAC1, MAC2,  MACn              |
          |            |------ +--------------------------------+
          |            |....   | MAC1, MAC2,  MACn              |
          +------------+------ +--------------------------------+
          | Nickname2  |VID-1  | MAC1, MAC2,  MACn              |
          |            |------ +--------------------------------+
          |            |VID-2  | MAC1, MAC2,  MACn              |
          |            |------ +--------------------------------+
          |            |...    | MAC1, MAC2,  MACn              |
          +------------+------ +--------------------------------+
          | -------    |------ +--------------------------------+
          |            |....   | MAC1, MAC2,  MACn              |
          +------------+------ +--------------------------------+
              Table 1: Summarized table pushed down from directory

       Whenever there is any change in MAC&VLAN <-> RBridgeEdge
       mapping, which can be triggered by hosts being added, moved, or
       de-commissioned, an incremental update can be sent to the
       RBridge edges which are impacted by the change.

   3.3. Messages to trigger pushing from directory

     In push down model, it is necessary to have a message for RBridge
     node to request directory server(s) to start pushing down the
     mapping entries. This message should at least include the number
     of VLANs enabled on the RBridge edge ports, so that directory
     server doesn't need to push down the entire mapping entries for
     all the hosts in the data center.

     RBridge node can use this message to get mapping entries when it
     is initialized or restarted.

4. Pull model of Directory Assisted RBridge Edge in DC Environment

   Under this model, ''RBridge'' pulls the MAC&VLAN<->RBridgeEdge mapping
   entry from the directory server when needed.

   RBridge edge node can send data frames with unknown DA to Directory
   Servers, or intercept all ARP/ND requests and forward them to the
   Directory Server(s).

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   The reply from the Directory Server can be the standard ARP/ND reply
   with an extra field showing the RBridge egress node's Nickname, as
   depicted in Table 2. RBridge ingress node can cache the mapping.

   If there is no response from the directory server, the RBridge edge
   node can drop the packet.

   RBridge edge can age out MAC&VLAN entries if they haven't been used
   for a certain period of time. Therefore, each RBridge edge will only
   keep the entries which are frequently used, i.e. mapping table size
   can be smaller.

   The following table shows how target RBridge nickname can be
   attached to a standard ARP Reply when replying to an ARP request
   forwarded by ingress RBridge edge.

        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
     | Hardware Type                 |        protocol Type          |
     | HLEN          |  PLEN         |     Operation           |
     |            Sender Hardware Address (MAC)                      |
     |Sender Hardware Address' cont  |  Sender Protocol Address (IP) |
     |Sender Protocol Address' cont  |  Target Hardware Address (MAC)|
     |             Target Hardware Address' cont (MAC)               |
     |             Target Protocol Address (IP)                      |
   ->|             Ingress RBridge's Nickname                        |
   ->|Ingress RBridge's Nickname ext |   Egress RBridge's Nickname   |
   ->|              Egress RBridge's Nickname extension              |
            Table 2: Extended fields added to standard ARP reply

   The original ARP reply format consists of the first 28 octets shown
   in this table. The last 12 octets in this table marked by ''->'' are
   extended fields to indicate the Ingress RBridge to which originating
   host is attached and the Egress RBridge to which the target host is
   attached. More bits are reserved for RBridge nicknames in case

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   multiple levels of nicknames are needed in the future for large data

   There are 16 bits for Operation type field in ARP message. IANA has
   assigned 0~25 for various purposes and leave 26~65534 unassigned
   If this approach is taken, a new ARP Operation code has to be
   assigned by IANA.

5. Push-Pull Hybrid Model

   For some edge nodes which have great number of VIDs enabled,
   managing the MAC&VLAN <-> RBridgeEdge mapping for hosts under all
   those VIDs can be challenge. This is especially true for Data Center
   gateway nodes, which need to maintain majority of VIDs if not all.

   For those RBridge Edge nodes, hybrid model should be considered.
   I.e. Push model are used for some VIDs, and pull model are used for
   other VIDs. It can be operator's decision (i.e. by configuration) on
   which VIDs' mapping entries are pushed down from directory and which
   VIDs' mapping entries are pulled.

   For example, in a data center when hosts in specific VIDs (vid#1,
   vid#2, ? vid#100)communicate regularly with external peers, the
   mapping entries for those 100 VIDs should be pushed down to the data
   center gateway routers. For hosts in other VIDs which only
   communicate with external peers once a day (or once a few days) for
   management interface, the mapping entries for those VIDs should be
   pulled down from directory whenever the needs come up.

6. To be continued

    This draft only describes the high level view of the mechanism on
    how to use directory to assist RBridge edge. More details will be

7. Manageability Considerations


8. Security Considerations


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9. IANA Considerations

   There are 16 bits for Operation type field. IANA has assigned 0~25
   for various purposes and leave 26~65534 unassigned
   If this approach is taken, a new ARP Operation code has to be
   assigned by IANA.

10. Acknowledgments

   This document was prepared using 2-Word-v2.0.template.dot.

11. References

   [Directory-assisted-RBridge] Dunbar, et, al ''Directory Assisted
   RBridge Edge'', <draft-dunbar-trill-directory-assisted-edge>, March

   [RBridges] Perlman, et, al ''RBridge: Base Protocol Specification'',
   <draft-ietf-trill-rbridge-protocol-16.txt>, March, 2010

   [RBridges-AF]   Perlman, et, al ''RBridges: Appointed Forwarders'',
   <draft-ietf-trill-rbridge-af-02.txt>, April 2011

   [ARMD-Problem] Dunbar, et,al, ''Address Resolution for Large Data
             Center Problem Statement'', Oct 2010.

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

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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
   45 West 18th Street 6th floor
   New York, NY 10011
   Email: igor@yahoo-inc.com

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