





Internet Engineering Task Force (IETF)                          M. Zhang
Request for Comments: 7727                                        H. Wen
Category: Standards Track                                         Huawei
ISSN: 2070-1721                                                    J. Hu
                                                           China Telecom
                                                            January 2016


                Spanning Tree Protocol (STP) Application
           of the Inter-Chassis Communication Protocol (ICCP)

Abstract

   The Inter-Chassis Communication Protocol (ICCP) supports an inter-
   chassis redundancy mechanism that is used to support high network
   availability.

   In this document, Provider Edge (PE) devices in a Redundancy Group
   (RG) running ICCP are used to offer multihomed connectivity to
   Spanning Tree Protocol (STP) networks to improve availability of the
   STP networks.  The ICCP TLVs and usage for the ICCP STP application
   are defined.

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 5741.

   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/rfc7727.















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Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.





































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Table of Contents

   1. Introduction ....................................................4
      1.1. Conventions Used in This Document ..........................4
      1.2. Terminology ................................................4
   2. Use Case ........................................................5
   3. Spanning Tree Protocol Application TLVs .........................6
      3.1. STP Connect TLV ............................................6
      3.2. STP Disconnect TLV .........................................7
           3.2.1. STP Disconnect Cause Sub-TLV ........................8
      3.3. STP Configuration TLVs .....................................8
           3.3.1. STP System Config ...................................9
           3.3.2. STP Region Name ....................................10
           3.3.3. STP Revision Level .................................10
           3.3.4. STP Instance Priority ..............................11
           3.3.5. STP Configuration Digest ...........................12
      3.4. STP State TLVs ............................................12
           3.4.1. STP Topology Changed Instances .....................12
           3.4.2. STP CIST Root Time Parameters ......................14
           3.4.3. STP MSTI Root Time Parameter .......................15
      3.5. STP Synchronization Request TLV ...........................16
      3.6. STP Synchronization Data TLV ..............................17
   4. Operations .....................................................18
      4.1. Common AC Procedures ......................................18
           4.1.1. Remote PE Node Failure or Isolation ................19
           4.1.2. Local PE Isolation .................................19
      4.2. ICCP STP Application Procedures ...........................19
           4.2.1. Initial Setup ......................................19
           4.2.2. Configuration Synchronization ......................20
           4.2.3. State Synchronization ..............................21
           4.2.4. Failure and Recovery ...............................22
   5. Security Considerations ........................................22
   6. IANA Considerations ............................................23
   7. References .....................................................23
      7.1. Normative References ......................................23
      7.2. Informative References ....................................24
   Acknowledgements ................................................. 24
   Authors' Addresses ............................................... 25













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1.  Introduction

   Inter-Chassis Communication Protocol (ICCP [RFC7275]) specifies a
   multi-chassis redundancy mechanism that enables Provider Edge (PE)
   devices located in a multi-chassis arrangement to act as a single
   Redundancy Group (RG).

   With the Spanning Tree Protocol (STP), a spanning tree will be formed
   over connected bridges by blocking some links between these bridges
   so that forwarding loops are avoided.  This document introduces
   support of STP as a new application of ICCP.  When a bridged STP
   network is connected to an RG, this STP application of ICCP enables
   the RG members to act as a single root bridge participating in the
   operations of STP.

   STP-relevant information needs to be exchanged and synchronized among
   the RG members.  New ICCP TLVs for the ICCP STP application are
   specified for this purpose.

   From the point of view of the customer, the Service Provider is
   providing a Virtual Private LAN Service (VPLS) [RFC4762].

1.1.  Conventions Used in This Document

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

1.2.  Terminology

   ICCP: Inter-Chassis Communication Protocol
   VPLS: Virtual Private LAN Service
   STP:  Spanning Tree Protocol
   MSTP: Multiple Spanning Tree Protocol
   MST:  Multiple Spanning Trees
   CIST: Common and Internal Spanning Tree ([802.1q], Section 3.27)
   MSTI: Multiple Spanning Tree Instance ([802.1q], Section 3.138)
   BPDU: Bridge Protocol Data Unit

   In this document, unless otherwise explicitly noted, the term "STP"
   also covers MSTP.










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2.  Use Case

   Customers widely use Ethernet as an access technology [RFC4762].
   It's common that one customer's Local Area Network (LAN) has multiple
   bridges connected to a carrier's network at different locations for
   reliability purposes.  Requirements for this use case are listed as
   follows.

   o  Customers desire to balance the load among their available
      connections to the carrier's network; therefore, all the
      connections need to be active.

   o  When one connection to the carrier network fails, customers
      require a connection in another location to continue to work after
      the reconvergence of the STP rather than compromising the whole
      STP network.  The failure of the connection may be due to the
      failure of the PE, the attachment circuit (AC), or even the
      Customer Edge (CE) device itself.

   In order to meet these requirements, the 'ICCP-STP' model is
   proposed.  It introduces STP as a new application of ICCP.

             +--------------+       +=============+
             |              |       |             |
             |              |       |             |
             |       +---+  |       |  +-----+|<--|--Pseudowire-->|
             |   +---+CE1+<6>-------<5>+ PE1 ||   |               |
             |  <1>  +---+  |       |  +-----+|<--|--Pseudowire-->|
             | +-+-+        |       |     ||      |
             | |CE3|        |       |     ||ICCP  |--> Towards the Core
             | +-+-+        |       |     ||      |
             |  <2>  +---+  |       |  +-----+|<--|--Pseudowire-->|
             |   +---+CE2+<3>-------<4>+ PE2 ||   |               |
             |       +---+  |       |  +-----+|<--|--Pseudowire-->|
             |              |       |             |
             | Multihomed   |       |  Redundancy |
             | STP Network  |       |    Group    |
             +--------------+       +=============+

        Figure 1: A STP network is multihomed to an RG running ICCP

   Figure 1 shows an example topology of this model.  With ICCP, the
   whole RG will be virtualized to be a single bridge.  Each RG member
   has its BridgeIdentifier (the MAC address).  The numerically lowest
   one is used as the BridgeIdentifier of the 'virtualized root bridge'.
   The RG acts as if the ports connected to the STP network (ports <4>
   and <5>) are for the same root bridge.  All these ports send the
   configuration BPDU with the highest root priority to trigger the



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   construction of the spanning tree.  The link between the peering PEs
   is not visible to the bridge domains of the STP network.  In this
   way, the STP will always break a possible loop within the multihomed
   STP network by breaking the whole network into separate islands so
   that each is attached to one PE.  That forces all PEs in the RG to be
   active.  This is different from a generic VPLS [RFC4762] where the
   root bridge resides in the customer network and the multihomed PEs
   act in the active-standby mode.  Note that the specification of VPLS
   remains unchanged other than for this operation.  For instance, a
   full-mesh of pseudowires (PWs) is established between PEs, and the
   "split horizon" rule is still used to perform the loop-breaking
   through the core.

3.  Spanning Tree Protocol Application TLVs

   This section specifies the ICCP TLVs for the ICCP STP application.
   The Unknown TLV bit (U-bit) and the Forward unknown TLV bit (F-bit)
   of the following TLVs MUST be sent as cleared and processed on
   receipt as specified in [RFC7275].

3.1.  STP Connect TLV

   This TLV is included in the RG Connect Message to signal the
   initiation of an ICCP STP application connection.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x2000               |    Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Protocol Version         |A|         Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Optional Sub-TLVs                        |
   ~                                                               ~
   |                                                               |
   +                                 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ...                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x2000 for "STP Connect TLV"







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      - Length

        Length of the TLV in octets excluding the U-bit, F-bit, Type,
        and Length fields.

      - Protocol Version

        The version of ICCP STP application protocol.  This document
        defines version 0x0001.

      - A bit

        Acknowledgement Bit.  Set to 1 if the sender has received a STP
        Connect TLV from the recipient.  Otherwise, set to 0.

      - Reserved

        Reserved for future use.  These bits MUST be sent as 0 and
        ignored on receipt.

      - Optional Sub-TLVs

        There are no optional Sub-TLVs defined for this version of the
        protocol.

3.2.  STP Disconnect TLV

   This TLV is used in the RG Disconnect Message to indicate that the
   connection for the ICCP STP application is to be terminated.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x2001               |    Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Optional Sub-TLVs                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x2001 for "STP Disconnect TLV"

      - Length

        Length of the TLV in octets excluding the U-bit, F-bit, Type,
        and Length fields.



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      - Optional Sub-TLVs

        The only optional Sub-TLV defined for this version of the
        protocol is the "STP Disconnect Cause" sub-TLV, defined below:

3.2.1.  STP Disconnect Cause Sub-TLV

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x200C              |    Length                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Disconnect Cause String                  |
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x200C for "STP Disconnect Cause TLV"

      - Length

        Length of the TLV in octets excluding the U-bit, F-bit, Type,
        and Length fields.

      - Disconnect Cause String

        Variable-length string specifying the reason for the disconnect,
        encoded in UTF-8 [RFC3629] format.  Used for operational
        purposes.

3.3.  STP Configuration TLVs

   The STP Configuration TLVs are sent in the RG Application Data
   Message.  When an STP Config TLV is received by a peer RG member, the
   member MUST synchronize with the configuration information contained
   in the TLV.  TLVs specified in Sections 3.3.1 to 3.3.5 define
   specific configuration information.











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3.3.1.  STP System Config

   This TLV announces the local node's STP System Parameters to the RG
   peers.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x2002               |    Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ROID                             |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         MAC Address                           |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x2002 for "STP System Config TLV"

      - Length

        Length of the ROID plus the MAC address in octets.  Always set
        to 14.

      - ROID

        Redundant Object Identifier; format defined in Section 6.1.3 of
        [RFC7275].

      - MAC Address

        The MAC address of the sender.  This MAC address is set to the
        BridgeIdentifier of the sender, as defined in [802.1q], Section
        13.26.2.  The numerically lowest 48-bit unsigned value of
        BridgeIdentifier is used as the MAC address of the Virtual Root
        Bridge mentioned in Section 2.









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3.3.2.  STP Region Name

   This TLV carries the value of Region Name.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x2003               |    Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Region Name                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x2003 for "STP Region Name TLV"

      - Length

        Length of the TLV in octets excluding the U-bit, F-bit, Type,
        and Length fields.

      - Region Name

        The Name of the MST Region as specified in [802.1q], Section
        3.142.

3.3.3.  STP Revision Level

   This TLV carries the value of Revision Level.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x2004               |    Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Revision Level          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x2004 for "STP Revision Level TLV".






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      - Length

        Length of the TLV in octets excluding the U-bit, F-bit, Type,
        and Length fields.  Always set to 2.

      - Revision Level

        The Revision Level as specified in [802.1q], Section 13.8, item
        c.

3.3.4.  STP Instance Priority

   This TLV carries the value of Instance Priority to other members in
   the RG.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x2005               |    Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Pri  |      InstanceID       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x2005 for "STP Instance Priority TLV"

      - Length

        Length of the TLV in octets excluding the U-bit, F-bit, Type,
        and Length fields.

      - Pri

        The Instance Priority.  It is interpreted as unsigned integer
        with higher value indicating a higher priority.

      - InstanceID

        The 12-bit Instance Identifier of the CIST or MSTI.  This
        parameter takes a value in the range 1 through 4094 for MSTI (as
        defined in [802.1q], Section 12.8.1.2.2) and takes value of 0
        for CIST.






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3.3.5.  STP Configuration Digest

   This TLV carries the value of STP VLAN Instance Mapping.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x2006             |    Length                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Configuration Digest                       |
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x2006 for "STP Configuration Digest TLV"

      - Length

        Length of the STP Configuration Digest in octets.  Always set to
        16.

      - Configuration Digest

        As specified in [802.1q], Section 13.8, item d.

3.4.  STP State TLVs

   The STP State TLVs are sent in the RG Application Data Message.  They
   are used by a PE device to report its STP status to other members in
   the RG.  Such TLVs are specified in the following subsections.

3.4.1.  STP Topology Changed Instances

   This TLV is used to report the Topology Changed Instances to other
   members of the RG.  The sender monitors Topology Change Notification
   (TCN) messages and generates this list.  The receiving RG member MUST
   initiate the Topology Change event, including sending BPDU with the
   Topology Change flag set to 1 out of the designated port(s) of the
   Topology Changed bridge domains of the STP network, and flushing out
   MAC addresses relevant to the instances listed in this TLV.

   If the PE device supports MAC Address Withdrawal (see Section 6.2 of
   [RFC4762]), it SHOULD send a Label Distribution Protocol (LDP)
   Address Withdraw Message with the list of MAC addresses towards the
   core over the corresponding LDP sessions.  It is not necessary to



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   send such a message to PEs of the same RG since the flushing of their
   MAC address tables should have been performed upon receipt of the STP
   Topology Changed Instances TLV.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x2007               |    Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       InstanceID List                         |
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x2007 for "STP Topology Changed Instances TLV"

      - Length

        Length of the TLV in octets excluding the U-bit, F-bit, Type,
        and Length fields.

      - InstanceID List

        The list of the InstanceIDs of the CIST or MSTIs whose
        topologies have changed as indicated by the TCN messages as
        specified in [802.1q], Section 13.14.  The list is formatted by
        padding each InstanceID value to the 16-bit boundary as follows,
        where the bits in the "R" fields MUST be sent as 0 and ignored
        on receipt.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |R|R|R|R| InstanceID#1          |R|R|R|R| InstanceID#2          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                             ... ...                           ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+











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3.4.2.  STP CIST Root Time Parameters

   This TLV is used to report the Value of CIST Root Time Parameters
   ([802.1q], Section 13.26.7) to other members of the RG.  All time
   parameter values are in seconds with a granularity of 1.  For ranges
   and default values of these parameter values, refer to [802.1d1998],
   Section 8.10.2, Table 8-3; [802.1d2004] Section 17.14, Table 17-1;
   and [802.1q], Section 13.26.7.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x2008               |    Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    MaxAge                     |   MessageAge                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    FwdDelay                   |   HelloTime                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | RemainingHops |
   +-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x2008 for "STP CIST Root Time TLV"

      - Length

        Length of the TLV in octets excluding the U-bit, F-bit, Type,
        and Length fields.  Always set to 9.

      - MaxAge

        The Max Age of the CIST.  It is the maximum age of the
        information transmitted by the bridge when it is the Root Bridge
        ([802.1d2004], Section 17.13.8).

      - MessageAge

        The Message Age of the CIST (see [802.1q], Section 13.26.7).

      - FwdDelay

        The Forward Delay of the CIST.  It is the delay used by STP
        Bridges to transition Root and Designated Ports to Forwarding
        ([802.1d2004], Section 17.13.5).




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      - HelloTime

        The Hello Time of the CIST.  It is the interval between periodic
        transmissions of Configuration Messages by Designated Ports
        ([802.1d2004], Section 17.13.6).

      - RemainingHops

        The remainingHops of the CIST ([802.1q], Section 13.26.7).

3.4.3.  STP MSTI Root Time Parameter

   This TLV is used to report the parameter value of MSTI Root Time to
   other members of the RG.  As defined in [802.1q], Section 13.26.7, it
   is the value of remainingHops for the given MSTI.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x2009              |    Length                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Pri  |  InstanceID           | RemainingHops |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x2009 for "STP MSTI Root Time TLV"

      - Length

        Length of the TLV in octets excluding the U-bit, F-bit, Type,
        and Length fields.  Always set to 3.

      - Pri

        The Instance Priority.  It is interpreted as an unsigned integer
        with higher value indicating a higher priority.

      - InstanceID

        The 12-bit Instance Identifier of the Multiple Spanning Tree
        Instance (MSTID).  As defined in [802.1q], Section 12.8.1.2.2,
        this parameter takes a value in the range 1 through 4094.






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      - RemainingHops

        The remainingHops of the MSTI.  It is encoded in the same way as
        in [802.1q], Section 14.4.1, item f.

3.5.  STP Synchronization Request TLV

   The STP Synchronization Request TLV is used in the RG Application
   Data Message.  This TLV is used by a device to request that its peer
   retransmit configuration or operational state.  The following
   information can be requested:

      - configuration and/or state of the STP system,
      - configuration and/or state for a given list of instances.

   The format of the TLV is 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x200A              |    Length                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Request Number           |C|S|   Request Type            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       InstanceID List                         |
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        Set to 0x200A for "STP Synchronization Request TLV"

      - Length

        Length of the TLV in octets excluding the U-bit, F-bit, Type,
        and Length fields.  Always set to 4.

      - Request Number

        2 octets.  Unsigned integer uniquely identifying the request.
        Used to match the request with a corresponding response.  The
        value of 0 is reserved for unsolicited synchronization, and it
        MUST NOT be used in the STP Synchronization Request TLV.  As
        indicated in [RFC7275], given the use of TCP, there are no
        issues associated with the wrap-around of the Request Number.




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      - C-bit

        Set to 1 if the request is for configuration data.  Otherwise,
        set to 0.

      - S-bit

        Set to 1 if the request is for running state data.  Otherwise,
        set to 0.

      - Request Type

        14 bits specifying the request type, encoded as follows:

            0x00   Request System Data
            0x01   Request data of the listed instances
            0x3FFF Request System Data and data of all instances

      - InstanceID List

        The InstanceIDs of the CIST or MSTIs; format specified in
        Section 3.4.1.

3.6.  STP Synchronization Data TLV

   The pair of STP Synchronization Data TLVs are used by the sender to
   delimit a set of TLVs that are being transmitted in response to an
   STP Synchronization Request TLV.  The delimiting TLVs signal the
   start and end of the synchronization data, and they associate the
   response with its corresponding request via the Request Number field.
   It's REQUIRED that each pair of STP Synchronization Data TLVs occur
   in the same fragment.  When the total size of the TLVs to be
   transmitted exceeds the maximal size of a fragment, these TLVs MUST
   be divided into multiple sets, delimited by multiple pairs of STP
   Synchronization Data TLVs, and filled into multiple fragments.  With
   the Request Number, lost fragments can be identified and
   re-requested.

   The STP Synchronization Data TLVs are also used for unsolicited
   advertisements of complete STP configuration and operational state
   data.  The Request Number field MUST be set to 0 in this case.










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   STP Synchronization Data TLV has the following format:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|   Type=0x200B              |    Length                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Request Number            |    Reserved                 |S|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      - U=F=0

      - Type

        set to 0x200B for "STP Synchronization Data TLV"

      - Length

        Length of the TLV in octets excluding the U-bit, F-bit, Type,
        and Length fields.  Always set to 4.

      - Request Number

        2 octets.  Unsigned integer identifying the Request Number of
        the "STP Synchronization Request TLV" that initiated this
        synchronization data response.

      - Reserved

        Reserved bits for future use.  These MUST be sent as 0 and
        ignored on receipt.

      - S

        S = 0: Synchronization Data Start
        S = 1: Synchronization Data End

4.  Operations

   Operational procedures for AC redundancy applications have been
   specified in Section 9.2 of [RFC7275].  The operational procedures of
   the ICCP STP application should follow those procedures, with the
   changes presented in this section.

4.1.  Common AC Procedures

   The following changes are introduced to the generic procedures of AC
   redundancy applications defined in Section 9.2.1 of [RFC7275].



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4.1.1.  Remote PE Node Failure or Isolation

   When a local PE device detects that a remote PE device that is a
   member of the same RG is no longer reachable (using the mechanisms
   described in Section 5 of [RFC7275]), the local PE device checks if
   it has redundancy ACs for the affected services.  If redundant ACs
   are present, and if the local PE device has the new highest bridge
   priority, the local PE device becomes the virtual root bridge for
   corresponding ACs.

4.1.2.  Local PE Isolation

   When a PE device detects that it has been isolated from the core
   network, then it needs to ensure that its AC redundancy mechanism
   will change the status of all active ACs to standby.  The AC
   redundancy application SHOULD then send an RG Application Data
   Message in order to trigger failover to another active PE device in
   the RG.  Note that this works only in the case of dedicated
   interconnect (Sections 3.2.1 and 3.2.3), since ICCP will still have
   the path to the peer, even though the PE device is isolated from the
   MPLS core network.

4.2.  ICCP STP Application Procedures

   This section defines the procedures of the ICCP STP application that
   are applicable for Ethernet ACs.

4.2.1.  Initial Setup

   When an RG is configured on a system that supports the ICCP STP
   application, such systems MUST send an RG Connect Message with an STP
   Connect TLV to each PE device that is a member of the RG.  The
   sending PE device MUST set the A bit to 1 in that TLV if it has
   received a corresponding STP Connect TLV from its peer PE; otherwise,
   the sending PE device MUST set the A bit to 0.  If a PE device
   receives an STP Connect TLV from its peer after sending its own TLV
   with the A bit set to 0, it MUST resend the TLV with the A bit set to
   1.  A system considers the ICCP STP application connection to be
   operational when it has both sent and received STP Connect TLVs with
   the A bit set to 1.  When the ICCP STP application connection between
   a pair of PEs is operational, the two devices can start exchanging RG
   Application Data Messages for the ICCP STP application.  This
   involves having each PE device advertise its STP configuration and
   operational state in an unsolicited manner.  A PE device SHOULD
   follow the order below when advertising its STP state upon initial
   application connection setup:





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      - Advertise the STP System Config TLV
      - Advertise remaining Configuration TLVs
      - Advertise State TLVs

   The update of the information contained in the State TLVs depends on
   that in the Configuration TLVs.  By sending the TLVs in the above
   order, the two peers may begin to update STP state as early as
   possible in the middle of exchanging these TLVs.

   A PE device MUST use a pair of STP Synchronization Data TLVs to
   delimit the entire set of TLVs that are being sent as part of this
   unsolicited advertisement.

   If a system receives an RG Connect Message with an STP Connect TLV
   that has a differing Protocol Version, it MUST follow the procedures
   outlined in the Section 4.4.1 ("Application Versioning") of
   [RFC7275].

   After the ICCP STP application connection has been established, every
   PE device MUST communicate its system-level configuration to its
   peers via the use of STP System Config TLV.

   When the ICCP STP application is administratively disabled on the PE,
   or on the particular RG, the system MUST send an RG Disconnect
   Message containing STP Disconnect TLV.

4.2.2.  Configuration Synchronization

   A system that supports ICCP STP application MUST synchronize the
   configuration with other RG members.  This is achieved via the use of
   STP Configuration TLVs.  The PEs in the RG MUST all agree on the
   common MAC address to be associated with the virtual root bridge.  It
   is possible to achieve this via consistent configuration on member
   PEs.  However, in order to protect against possible
   misconfigurations, a virtual root bridge identifier MUST be set to
   the MAC address advertised by the PE device with the numerically
   lowest BridgeIdentifier (i.e., the MAC address of the bridge) in the
   RG.

   Furthermore, for a given ICCP STP application, an implementation MUST
   advertise the configuration prior to advertising its corresponding
   state.  If a PE device receives any STP State TLV that it had not
   learned of before via an appropriate STP Configuration TLV, then the
   PE device MUST request synchronization of the configuration and state
   from its peer.  If during such synchronization a PE device receives a
   State TLV that it has not learned before, then the PE device MUST
   send a NAK TLV for that particular TLV.  The PE device MUST NOT
   request resynchronization in this case.



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4.2.3.  State Synchronization

   PEs within the RG need to synchronize their state for proper STP
   operation.  This is achieved by having each system advertise its
   running state in STP State TLVs.  Whenever any STP parameter either
   on the CE or PE side is changed, the system MUST transmit an updated
   TLV for the affected STP instances.  Moreover, when the
   administrative or operational state changes, the system MUST transmit
   an updated State TLV to its peers.

   A PE device MAY request its peer to retransmit previously advertised
   state.  This is useful in case the PE device is recovering from a
   soft failure and attempting to relearn state.  To request such
   retransmissions, a PE device MUST send a set of one or more STP
   Synchronization Request TLVs.

   A PE device MUST respond to a STP Synchronization Request TLV by
   sending the requested data in a set of one or more STP Configuration
   or State TLVs delimited by a pair of STP Synchronization Data TLVs.

   Note that the response may span across multiple RG Application Data
   Messages, for example, when MTU limits are exceeded; however, the
   above ordering MUST be retained across messages, and only a single
   pair of Synchronization Data TLVs MUST be used to delimit the
   response across all RG Application Data Messages.

   A PE device MAY readvertise its STP state in an unsolicited manner.
   This is done by sending the appropriate State TLVs delimited by a
   pair of STP Synchronization Data TLVs and using a Request Number of
   0.

   While a PE device has sent out a synchronization request for a
   particular PE device, it SHOULD silently ignore all TLVs that are
   from that node, are received prior to the synchronization response,
   and carry the same type of information being requested.  This saves
   the system from the burden of updating state that will ultimately be
   overwritten by the synchronization response.  Note that TLVs
   pertaining to other systems should continue to be processed normally.

   If a PE device receives a synchronization request for an instance
   that doesn't exist or is not known to the PE, then it MUST trigger
   the unsolicited synchronization of all information by restarting the
   initialization.

   If during the synchronization operation a PE device receives an
   advertisement of a Node ID value that is different from the value
   previously advertised, then the PE device MUST purge all state data
   previously received from that peer prior to the last synchronization.



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4.2.4.  Failure and Recovery

   When a PE device that is active for the ICCP STP application
   encounters a core isolation fault [RFC7275], it SHOULD attempt to
   fail over to a peer PE device that hosts the same RG.  The default
   failover procedure is to have the failed PE device bring down the
   link(s) towards the multihomed STP network.  This will cause the STP
   network to reconverge and to use the other links that are connected
   to the other PE devices in the RG.  Other procedures for triggering
   failover are possible and are outside the scope of this document.

   If the isolated PE device is the one that has the numerically lowest
   BridgeIdentifier, PEs in the RG MUST synchronize STP Configuration
   and State TLVs and determine a new virtual root bridge as specified
   in Section 4.2.2.

   Upon recovery from a previous fault, a PE device SHOULD NOT reclaim
   the role of the virtual root for the STP network even if it has the
   numerically lowest BridgeIdentifier among the RG.  This minimizes
   traffic disruption.

   Whenever the virtual root bridge changes, the STP Topology Changed
   Instances TLV lists the instances that are affected by the change.
   These instances MUST undergo a STP reconvergence procedure when this
   TLV is received as defined in Section 3.4.1.

5.  Security Considerations

   This document specifies an application running on the channel
   provided by ICCP [RFC7275].  The security considerations on ICCP
   apply in this document as well.

   For the ICCP STP application, an attack on a channel (running in the
   provider's network) can break not only the ability to deliver traffic
   across the provider's network, but also the ability to route traffic
   within the customer's network.  That is, a careful attack on a
   channel (such as the DoS attacks as described in [RFC7275]) can break
   STP within the customer network.  Implementations need to provide
   mechanisms to mitigate these types of attacks.  For example, the port
   between the PE device and the malicious CE device may be blocked.











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6.  IANA Considerations

   The IANA maintains a top-level registry called "Pseudowire Name
   Spaces (PWE3)".  It has a subregistry called "ICC RG Parameter
   Types".

   IANA has made 13 allocations from this registry as shown below.  IANA
   has allocated the codepoints from the range marked for assignment by
   IETF Review (0x2000-0x2FFF) [RFC5226].  Each assignment references
   this document.

      Parameter Type Description
      -------------- ---------------------------------
      0x2000         STP Connect TLV
      0x2001         STP Disconnect TLV
      0x2002         STP System Config TLV
      0x2003         STP Region Name TLV
      0x2004         STP Revision Level TLV
      0x2005         STP Instance Priority TLV
      0x2006         STP Configuration Digest TLV
      0x2007         STP Topology Changed Instances TLV
      0x2008         STP CIST Root Time TLV
      0x2009         STP MSTI Root Time TLV
      0x200A         STP Synchronization Request TLV
      0x200B         STP Synchronization Data TLV
      0x200C         STP Disconnect Cause TLV

7.  References

7.1.  Normative References

   [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>.

   [RFC3629]    Yergeau, F., "UTF-8, a transformation format of ISO
                10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
                2003, <http://www.rfc-editor.org/info/rfc3629>.

   [RFC4762]    Lasserre, M., Ed., and V. Kompella, Ed., "Virtual
                Private LAN Service (VPLS) Using Label Distribution
                Protocol (LDP) Signaling", RFC 4762,
                DOI 10.17487/RFC4762, January 2007,
                <http://www.rfc-editor.org/info/rfc4762>.






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   [RFC7275]    Martini, L., Salam, S., Sajassi, A., Bocci, M.,
                Matsushima, S., and T. Nadeau, "Inter-Chassis
                Communication Protocol for Layer 2 Virtual Private
                Network (L2VPN) Provider Edge (PE) Redundancy",
                RFC 7275, DOI 10.17487/RFC7275, June 2014,
                <http://www.rfc-editor.org/info/rfc7275>.

   [802.1q]     IEEE, "IEEE Standard for Local and Metropolitan Area
                Networks -- Bridges and Bridged Networks", IEEE Std
                802.1Q-2014, DOI 10.1109/IEEESTD.2014.6991462, 2014.

   [802.1d1998] IEEE, "Information technology -- Telecommunications and
                information exchange between systems -- Local and
                metropolitan area networks -- Common specifications --
                Part 3: Media Access Control (MAC) Bridges", ANSI/IEEE
                Std 802.1D-1998, DOI 10.1109/IEEESTD.1998.95619, 1998.

   [802.1d2004] IEEE, "IEEE Standard for Local and metropolitan area
                networks -- Media Access Control (MAC) Bridges", IEEE
                Std 802.1D-2004, DOI 10.1109/ieeestd.2004.94569, 2004.

7.2.  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>.

Acknowledgements

   The authors would like to thank the comments and suggestions from
   Ignas Bagdonas, Adrian Farrel, Andrew G. Malis, Gregory Mirsky, and
   Alexander Vainshtein.


















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Authors' Addresses

   Mingui Zhang
   Huawei Technologies
   No. 156 Beiqing Rd. Haidian District,
   Beijing 100095
   China

   Email: zhangmingui@huawei.com


   Huafeng Wen
   Huawei Technologies
   101 Software Avenue,
   Nanjing 210012
   China

   Email: wenhuafeng@huawei.com


   Jie Hu
   China Telecom
   Beijing Information Science & Technology Innovation Park
   Beiqijia Town Changping District,
   Beijing 102209
   China

   Email: hujie@ctbri.com.cn























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