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Layer 2 Gateway (L2GW)

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Liang Xia , Lucy Yong
Last updated 2014-02-13
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Network working group                                           L. Xia
Internet Draft                                                  L. Yong
Category: Standard Track                                        Huawei

Expires: September 2014                               February 14, 2014

                          Layer 2 Gateway (L2GW)


   Layer 2 Gateway (L2GW) is used for interconnecting layer 2 overlay
   network [NVO3FRWK] with layer 2 bridge networks [IEEE802.1Q] to form
   one layer 2 virtual network. This draft discusses which Layer 2
   Control Protocol (L2CP) specified in IEEE802.1 should be supported
   by the layer 2 overlay network and which not, and specifies how L2GW
   should deal with L2CP frames.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
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Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( 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.

Table of Contents

   1. Introduction ................................................ 3
      1.1. Conventions used in this document ...................... 4
      1.2. Terminology ............................................ 4
   2. L2GW Reference Model......................................... 4
   3. L2CP Review and Applicability to L2 Overlay Network.......... 5
      3.1. STP/RSTP/MSTP .......................................... 7
      3.2. PAUSE .................................................. 7
      3.3. LACP/LAMP .............................................. 7
      3.4. Link OAM ............................................... 8
      3.5. Port Authentication .................................... 9
      3.6. E-LMI .................................................. 9
      3.7. LLDP ................................................... 9
      3.8. PTP Peer Delay ........................................ 10
      3.9. ESMC .................................................. 10
      3.10. GARP/MRP Block........................................ 10
   4. L2CP Process in L2GW........................................ 10
      4.1. L2CP Frames Filtered (Peered or Discarded) in L2GW .... 11
      4.2. L2CP Frames Passed through L2GW ....................... 11
   5. Other Interworking Cases ................................... 12
   6. Security Considerations .................................... 12
   7. IANA Considerations ........................................ 12
   8. References ................................................. 12
      8.1. Normative References .................................. 12
      8.2. Informative References ................................ 13

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1. Introduction

   Cloud computing and network virtualization is evolving to the
   direction of virtualized networks in overlay, which aims fast and
   easy to create tenant networks, support tenant system mobility, and
   bring the manageability of all virtualized resources in DC.

   Layer 2 (L2) overlay network in NVO3 means an L2 overlay network
   interconnecting tenant systems, where any pair of Network
   Virtualization Edges (NVE) are connected by IP tunnels. As a result,
   it forms a full mesh topology of overlay network, i.e. only one hop
   between any pair of NVEs. L2 bridge network in this draft is the
   network specified in IEEE 802.1Q [IEEE 802.1Q] which are widely
   deployed in DCs. L2 overlay network is used to refer the L2 network
   specified in NVO3.

   During DC network migration, it's very common that L2 overlay
   network may be mix used with L2 bridge network in a DC, and the
   communication between them is required. In another use case, using
   L2 bridge network to connect non-virtualized devices in DC are
   mature and well deployed method in DC; these non-virtualized devices
   are necessary for some applications such as BIG data and are
   required to communicate with virtualized resources.

   To interconnect an L2 overlay network with an L2 bridge network,
   gateway functions are needed on the device(s)/system(s) connecting
   two networks. This device is referred as to Layer 2 Gateway (L2GW)
   in this draft. L2GW processes the encapsulation translation of
   packets between overlay technologies (e.g., VxLAN [VXLAN], NVGRE
   [NVGRE]) and the technologies specified in IEEE 802.1Q; it also
   deals with Layer 2 Control Protocol (L2CP) frames from the bridge

   L2CP frames are defined by IEEE802.1 to be used for L2 network
   control, e.g., STP, LACP, etc. An L2CP is identified by one of the
   following MAC destination addresses:

   o 01-80-C2-00-00-00 through 01-80-C2-00-00-0F: Bridge Block of

   o 01-80-C2-00-00-20 through 01-80-C2-00-00-2F: GARP/MRP Block of

   All L2CPs are supported in a L2 bridge network, every 802.1Q bridge
   performs corresponding action, i.e., peer (to be processed by local
   protocol entity), discard, pass, based on L2CP frame's MAC
   destination address (DA) and protocol identifier (Ethertype or LLC

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   Address). For L2 overlay VN, most of L2CPs are unnecessary because
   L2 overlay VN has its own control plane functions to support needed
   L2 communication such as transport over a tunnel or OAM. It is very
   useful to document how these service frames should be handled at
   L2GW to ensure that two networks can interwork.

   This draft discusses which L2CP should be supported by L2 overlay
   network and which not, and specifies how L2GW should deal with L2CP

    1.1. Conventions used in this document

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

    1.2. Terminology

   This document uses the terms defined in NVO3 framework [NVO3FRWK]
   and architecture [NVO3ARCH] documents.

2. L2GW Reference Model

   The following diagram shows a reference model where L2GW provides an
   interconnection between L2 overlay network and L2 bridge network.

                .........                   .........
           +---+         ...           ....          . +------+
       TSs-+NVE|            +---------+              +-+Server|
           +---+ L2 Overlay |         |  L2 Bridge   . +------+
             .    Network   |  L2GW   |   Network    .
             .              |         |              . +------+
         ..+---+            +---------+              +-+Server|
       TSs-+NVE|         ...           ....        ... +------+
           +---+.........                  ........

                      Figure 1: L2GW Reference Model

   L2GW can reside on access switch providing direct connection with
   physical server, or reside on core switch or edge router providing
   connection with L2 bridge network.

   Note that this draft only addresses the case that L2GW and L2 NVE
   are co-located at the edge device between two L2 networks, where
   L2GW can deal with the interworking work. Other cases are not yet
   covered in this draft.

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3. L2CP Review and Applicability to L2 Overlay Network

   L2CP protocols defined in IEEE 802.1 are listed in Table 1:

   |MAC DA            |Assignment| Protocol |      L2CP Action    |
   |                  |          |  Type    +----------+----------+
   |                  |          |          |VLAN-based|PORT-based|
   |                  |          |          |    L2    |    L2    |
   |                  |          |          | services | services |
   |01-80-C2-00-00-00 |Nearest   |STP/RSTP/M|Filter    |Pass      |
   |                  |Customer  |STP,      |          |          |
   |                  |Bridge    |LACP/LAMP |          |          |
   |01-80-C2-00-00-01 |IEEE MAC  |PAUSE     |Filter    |Filter    |
   |                  |Specific  |          |          |          |
   |                  |Control   |          |          |          |
   |                  |Protocols |          |          |          |
   |01-80-C2-00-00-02 |IEEE 802  |LACP/LAMP,|Filter    |Filter    |
   |                  |Slow      |Link OAM, |          |          |
   |                  |Protocols |ESMC      |          |          |
   |01-80-C2-00-00-03 |Nearest   |Port      |Filter    |Filter    |
   |                  |non-TPRM  |Authentica|          |          |
   |                  |Bridge    |tion,     |          |          |
   |                  |          |LACP/LAMP |          |          |
   |01-80-C2-00-00-04 |IEEE MAC  |          |Filter    |Filter    |
   |                  |Specific  |          |          |          |
   |                  |Control   |          |          |          |
   |                  |Protocols |          |          |          |
   |01-80-C2-00-00-05 |Reserved  |          |Filter    |Filter    |
   |                  |for Future|          |          |          |
   |01-80-C2-00-00-06 |Standardiz|          |          |          |
   |                  |ation     |          |          |          |
   |01-80-C2-00-00-09 |          |          |          |          |
   |                  |          |          |          |          |
   |01-80-C2-00-00-0A |          |          |          |          |

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   |01-80-C2-00-00-07 |MEF ELMI  |E-LMI     |Filter    |Filter    |
   |01-80-C2-00-00-08 |Provide   |          |Filter    |Filter    |
   |                  |Bridge    |          |          |          |
   |                  |Group     |          |          |          |
   |01-80-C2-00-00-0B |Reserved  |          |Filter    |Pass      |
   |                  |for Future|          |          |          |
   |01-80-C2-00-00-0C |Standardiz|          |          |          |
   |                  |ation     |          |          |          |
   |01-80-C2-00-00-0D |Provider  |          |Filter    |Pass      |
   |                  |Bridge    |          |          |          |
   |                  |MVRP      |          |          |          |
   |01-80-C2-00-00-0E |Nearest   |LLDP, PTP |Filter    |Filter    |
   |                  |Bridge,   |Peer Delay|          |          |
   |                  |Individual|          |          |          |
   |                  |LAN Scope |          |          |          |
   |01-80-C2-00-00-20 |          |GARP/MRP  |Pass      |Pass      |
   |                  |          |Block     |          |          |
   |      through     |          |          |          |          |
   |                  |          |          |          |          |
   |01-80-C2-00-00-2F |          |          |          |          |

                   Table 1 L2CP protocols specification


      Different L2CP protocols can use the same MAC DA in above block of
      32 addresses, but be differentiated by protocol identifier. MAC DA
      determines the intended recipient device for the frame;

      Filter represent the L2CP action of peer or discard;

      Based on whether L2 interface is VLAN-aware, L2 services can
      divided into two categories: VLAN-based L2 services, PORT-based L2
      services. L2CP action (peer, discard, pass) for these two L2
      services is also different;

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      Whether the L2CP frames are peered or discarded is further
      determined by the configuration of L2 interface.

   Further analysis about whether a L2CP protocol is necessary and how
   it is processed in NVO3 supported L2 VN, is provided in the
   following sub sections.

    3.1. STP/RSTP/MSTP

   The Spanning Tree Protocol (STP) is a L2 protocol that ensures a
   loop-free topology for any bridged Ethernet local area network.  The
   basic function of STP is to prevent bridge loops and the broadcast
   storm that results from them. Rapid spanning Tree Protocol (RSTP)
   and Multiple Spanning Tree Protocol (MSTP) are all the enhanced xSTP

   L2 overlay network does not need xSTP protocols to prevent bridge
   loops because it has its own mechanism for it, i.e., NVA, control
   plane mechanisms, full mesh + split horizon, etc. So, the process of
   xSTP frames in L2 VN is:

      Be in line with L2CP protocols' specification of Table 1 from IEEE
      in the L2 sub-networks attached to L2 NVEs;

      xSTP frames are filtered in L2 NVEs and should not go into L2
      overlay network.

    3.2. PAUSE

   [IEEE 802.3-2005] has specified a L2 flow control mechanism through
   using the PAUSE frame. This frame uses L2CP MAC DA of 01-80-C2-00-
   00-01 to be sent to the node at the other end of the link for
   informing it to halt the frame transmission for a specified period
   of time.

   When L2 NVE is co-located in Hypervisor, PAUSE frame is not
   necessary in one device. When they are separated, PAUSE frame is
   only used in layer 2 network between L2 NVE and Hypervisor, there is
   no need to overlay PAUSE frame between L2 NVEs.

    3.3. LACP/LAMP

   Link Aggregation [IEEE 802.1AXbk-2012] is a mechanism for making
   multiple point-to-point links between a pair of devices appear to be
   a single logical link between those devices. Link Aggregation

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   Control Protocol (LACP) and Link Marker Control Protocol (LAMP)
   operate between exactly two peer devices for the purpose of creating,
   verifying, and monitoring the logical link created by aggregating
   individual links.  Specific L2CP frames, known as Link Aggregation
   Control Protocol Data Units (LACPDUs), are exchanged between the
   peer devices on each individual link in the aggregation.  The
   protocol identifier used by LACP is an Ethertype with a value of
   0x8809 (the ''Slow Protocols'' Ethertype) and subtype values 01 (for
   LACP) and 02 (for LAMP). Note that LACP is used to represent LACP
   and LAMP in the following text.

   LACP uses 3 different L2CP MAC DAs to determine the scope of
   propagation of LACPDUs within a bridged LAN, as Table 2 follows:

   |Assignment      | L2CP MAC DA      |Peered or discarded by       |
   |Nearest Customer| 01-80-C2-00-00-00|End Station, Customer Bridge,|
   |Bridge          |                  |Provider Edge Bridge         |
   |IEEE 802 Slow   | 01-80-C2-00-00-02|End Station, Customer Bridge,|
   |Protocols       |                  |Provider Edge Bridge,        |
   |                |                  |Provider Bridge              |
   |Nearest non-TPRM| 01-80-C2-00-00-03|Bridges except for Two Port  |
   |Bridge          |                  |MAC Relay                    |
                Table 2 LACP specification of L2CP MAC DAs

   Base on the summary of Table 2, LACPDUs with the L2CP MAC DA of 01-
   80-C2-00-00-02 are peered or discarded by every node, so this kind
   of LACPDUs will not be overlaid across the L2 overlay network. For
   01-80-C2-00-00-00, it is possible that LACPDUs need to be overlaid
   across Provider Bridge and L2 NVEs of L2 overlay network to reach
   the other end Custom Bridge, L2 overlay network maybe need to
   support to overlay this kind of LACP frame between L2 NVEs. How the
   L2 overlay network support LACP frame of 01-80-C2-00-00-03 is TBD.

    3.4. Link OAM

   Lin OAM defined is defined in [IEEE 802.3ah], as mechanisms for
   monitoring and troubleshooting Ethernet access links. Specifically
   it defines tools for discovery, remote failure indication, remote
   and local loopbacks and status and performance monitoring.

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   The Link OAM frames using L2CP MAC DA of 01-80-C2-00-00-02 are
   peered or discarded by every node, so this kind of frame will not be
   overlaid across the L2 overlay network.

    3.5. Port Authentication

   [IEEE 802.1X] is an IEEE Standard for Port-based Network Access
   Control (PNAC). It is part of the IEEE 802.1 group of networking
   protocols. It provides an authentication mechanism to devices
   wishing to attach to a LAN or WLAN.

   Whether or not the L2 overlay network needs to overlay this L2CP
   frames is TBD.

    3.6. E-LMI

   Ethernet Local Management Interface (E-LMI) is a protocol between
   the customer edge (CE) device and the provider edge (PE) device. It
   runs only on the PE-CE UNI link and notifies the CE of connectivity
   status and configuration parameters of Ethernet services available
   on the CE port. E-LMI interoperates with an OAM protocol, such as
   Connectivity Fault Management (CFM), that runs within the provider
   network to collect OAM status. CFM runs at the provider maintenance
   level (UPE to UPE with inward-facing MEPs at the UNI). E-LMI relies
   on the OAM Ethernet Infrastructure (EI) to interwork with CFM for
   end-to-end status of Ethernet virtual connections (EVCs) across CFM

   The LLDP frames using L2CP MAC DA of 01-80-C2-00-00-07 are peered or
   discarded by every node except for the Two Port MAC Relay (TPMR)
   bridge, so this kind of frame will not be overlaid across the L2
   overlay network.

    3.7. LLDP

   The Link Layer Discovery Protocol (LLDP) is a vendor-neutral link
   layer protocol in the Internet Protocol Suite used by network
   devices for advertising their identity, capabilities, and neighbors
   on an IEEE 802 local area network, principally wired Ethernet. The
   protocol is formally referred to by the IEEE as Station and Media
   Access Control Connectivity Discovery specified in standards
   document [IEEE 802.1AB].

   The LLDP frames using L2CP MAC DA of 01-80-C2-00-00-0E are peered or
   discarded by every node, so this kind of frame will not be overlaid
   across the L2 overlay network.

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    3.8. PTP Peer Delay

   PTP Peer Delay frame is specified in [IEEE 1588-2008] to carry PTP
   peer time information. It uses L2CP MAC DA of 01-80-C2-00-00-0E and
   peered or discarded by every node, so this kind of frame will not be
   overlaid across the L2 overlay network.

    3.9. ESMC

   Ethernet Synchronization Messaging Channel (ESMC) is specified in
   [ITU-T Rec. G.8264] for conveying clock information between
   Synchronous Ethernet (SyncE) bridges.

   The ESMC frames using L2CP MAC DA of 01-80-C2-00-00-02 are peered or
   discarded by every node, so this kind of frame will not be overlaid
   across the L2 overlay network.

    3.10. GARP/MRP Block

   Multiple Registration Protocol (MRP), which replaced Generic
   Attribute Registration Protocol (GARP), is a generic registration
   framework defined by the [IEEE 802.1ak] amendment to the [IEEE
   802.1Q] standard. MRP allows bridges, switches or other similar
   devices to be able to register and de-register attribute values,
   such as VLAN identifiers and multicast group membership across a
   large LAN. MRP operates at the Data Link Layer.

   The block of L2CP MAC DA from 01-80-C2-00-00-20 to 01-80-C2-00-00-2F
   is used for MRP protocol. Now, only 01-80-C2-00-00-20 is for
   Multiple MAC Registration Protocol (MMRP) and 01-80-C2-00-00-21 is
   for Multiple VLAN Registration Protocol (MVRP), other L2CP MAC DA of
   the block are all reserved for future use. Protocol use one address
   of this block is passed by all the intervening bridges that does not
   participate in the protocol using this address, and peered or
   discarded by the bridge that participate in the protocol at last.
   This forwarding rule maybe requires MRP frames to be overlaid across
   the L2 overlay network.

4. L2CP Process in L2GW

   For all L2CP protocols, several differences exist between L2 overlay
   network and L2 bridge network on how to process them. As the
   demarcation point between L2 overlay network and L2 bridge network,
   L2GW keeps the same action to all L2CP frames as before at the L2
   bridge network side on the one hand, but maybe processes some L2CP
   frames differently at the L2 overlay network side on the other hand.
   The following sub sections will describe the L2CP process in L2GW.

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   4.1. L2CP Frames Filtered (Peered or Discarded) in L2GW

   Although xSTP protocols using Nearest Customer Bridge address of 01-
   80-C2-00-00-00 indicate that it can be overlaid across L2 overlay
   network, they still are not necessary for L2 overlay network because
   L2 overlay network has its own mechanism to prevent bridge loops. So
   xSTP frames will be filtered by the L2GW and not go into the L2
   overlay network.

   Based on the analysis of section 3.3, LACP/LAMP frames using IEEE
   802 Slow Protocols of 01-80-C2-00-00-02 are not necessary for L2
   overlay network.  So, LACP/LAMP frames will be filtered by the L2GW
   and not go into the L2 overlay network. ESMC frames using the same
   MAC DA will also be filtered by L2GW.

   For Link OAM frames, if OAM functions are necessary for the whole L2
   network which interconnects L2 bridge network and L2 overlay network,
   L2GW needs to support the interworking of OAM as well. This means
   that L2GW should peer the Link OAM frames of L2 bridge network and
   perform some actions between NVEs in L2 overlay network. The
   detailed operation is TBD.

   Other L2CP protocols that are filtered by L2GW and do not go into L2
   overlay network include PAUSE, E-LMI, LLDP, PTP Peer Delay. The
   basic reason is that they all require to be processed hop by hop in
   L2 network strictly, but overlay network breaks this rule.

   The action of ''filter'' can be ''peer'', or ''discard''. It depends on
   the specific service requirement, i.e., does L2GW need to
   participate in the L2CP protocol, etc. How to determine the specific
   action is TBD.

   4.2. L2CP Frames Passed through L2GW

   Excepting for the aforementioned L2CP protocols filtered by L2GW,
   the left L2CP protocols need to be passed through L2GW. They include:

      LACP/LAMP frames using IEEE 802 Slow Protocols of 01-80-C2-00-00-

      GARP/MRP series protocols (i.e., MMRP, MVRP) using the MAC DA
      block of 01-80-C2-00-00-20 through 01-80-C2-00-00-2F.

   All these kinds of L2CP frames are passed through L2GW and traverse
   across the L2 overlay network and L2 bridge network to arrive the
   bridges that participate in the L2CP protocols. For MRP protocols,
   another necessary operation of L2GW is to use the pre-provisioned

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   VLAN to virtual network instance (VNI) mappings in NVE locally or by
   getting from NVA to map these MRP frames into corresponding VNIs.

5. Other Interworking Cases

   There are other L2 bridge network technologies that use L2 Control
   Plane protocols such as Provider Bridge [IEEE802.1AD] or Provider
   Backbone Bridge [PBB] [IEEE802.1AH]. The use case of L2 Overlay
   Network interworking with these types of bridge networks is for the
   further study.

   Note that VPLS [RFC4761] [RFC4762], EVPN [EVPN], Shortest Path
   Bridging [IEEE SPB] and TRILL [RFC6325] are also technologies for L2
   private network implementation. These technologies rely on the
   control plane protocol and aim for service provider network. SDN
   controller interworking with such control plane protocol will be
   addressed in separate draft.

6. Security Considerations


7. IANA Considerations

   The document does not require any IANA action.

8. References

    8.1. Normative References

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

   [RFC4761] Kompella, K. and Rekhter, Y. (Editors), "Virtual Private
   LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling", RFC
   4761, January 2007

   [RFC4762] Lasserre, M. and Kompella, V. (Editors), "Virtual Private
   LAN Service (VPLS) Using Label Distribution Protocol (LDP)
   Signaling", RFC 4762, January 2007.

   [RFC6325]  Perlman, R., "RBridges: Base Protocol Specification",
   July 2011.

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    8.2. Informative References

   [NVO3ARCH] Black, D, Narten, T., et al, "An Architecture for Overlay
   Networks (NVO3)", draft-narten-nvo3-arch-01, work in progress

   [NVO3FRWK] LASSERRE, M., Motin, T., et al, "Framework for DC Network
   Virtualization", draft-ietf-nvo3-framework-03, work in progress.

   [NVGRE]  Sridharan, M., et al, "NVGRE: Network Virtualization using
   Generic Routing Encapsulation", draft-sridharan-virtualization-
   nvgre-03, work in progress

   [VXLAN]  Mahalingam, M., Dutt, D., etc, "VXLAN: A Framework for
   Overlaying Virtualized Layer 2 Networks over Layer 3 Networks",
   draft-mahalingam-dutt-dcops-vxlan-05.txt, work in progress

   [EVPN] Sajassi, A. and R. Aggarwal, "BGP MPLS Based Ethernet VPN",
   draft-ietf-l2vpn-evpn-04, July 2013

   [IEEE 802.1Q] "Virtual Bridged Local Area Networks", 2005

   [IEEE 802.3-2005] "Part 3: Carrier sense multiple access with
   collision detection (CSMA/CD) access method and physical layer

   [IEEE 802.1AXbk-2012] "IEEE Standard for Local and metropolitan area
   networks--Link Aggregation Amendment 1: Protocol Addressing"

   [IEEE 802.3ah] "IEEE Standard for Information technology--Local and
   metropolitan area networks--Part 3: CSMA/CD Access Method and
   Physical Layer Specifications Amendment: Media Access Control
   Parameters, Physical Layers, and Management Parameters for
   Subscriber Access Networks"

   [IEEE 802.1X] "IEEE Standard for Local and metropolitan Area
   Networks. Port-based Network Access Control"

   [IEEE 802.1AB] "IEEE Standard for Station and Media Access Control,
   Connectivity Discovery"

   [IEEE 1588-2008] "IEEE Standard for a Precision Clock
   Synchronization Protocol for Networked Measurement and Control

   [IEEE 802.1ak] "IEEE Standard for Local and metropolitan Area
   Networks - Virtual Bridged Local Area Networks, Amendment 7:
   Multiple Registration Protocol"

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   [IEEE 802.1AD], "Virtual Bridged Local Area Networks - Amendment 4:
   Provider Bridges", 2005

   [PBB] Clauses 25 and 26 of "IEEE Standard for Local and metropolitan
   area networks - Media Access Control (MAC) Bridges and Virtual
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   [IEEE802.1AH] IEEE Draft P802.1ah/D4.2 "Virtual Bridged Local Area
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   [IEEE SPB] "IEEE standard for local and metropolitan area networks:
   Media access control (MAC) bridges and virtual bridged local area
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   [ITU-T Rec. G.8264] "Distribution of Timing Through Packet Networks"

   Authors' Addresses

   Liang Xia
   Huawei Technologies


   Lucy Yong
   Huawei Technologies, USA


Xia & Yong                                                  [Page 14]