





Network Working Group                                            S. Shah
Request for Comments: 3619                                        M. Yip
Category: Informational                                 Extreme Networks
                                                            October 2003


                           Extreme Networks'
             Ethernet Automatic Protection Switching (EAPS)
                               Version 1

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes the Ethernet Automatic Protection Switching
   (EAPS) (tm) technology invented by Extreme Networks to increase the
   availability and robustness of Ethernet rings.  An Ethernet ring
   built using EAPS can have resilience comparable to that provided by
   SONET rings, at a lower cost and with fewer constraints (e.g., ring
   size).

1.  Introduction

   Many Metropolitan Area Networks (MANs) and some Local Area Networks
   (LANs) have a ring topology, as the fibre runs.  The Ethernet
   Automatic Protection Switching (EAPS) technology described here works
   well in ring topologies for MANs or LANs.

   Most MAN operators want to minimise the recovery time in the event
   that a fibre cut occurs.  The Ethernet Automatic Protection Switching
   (EAPS) technology described here converges in less than one second,
   often in less than 50 milliseconds.  EAPS technology does not limit
   the number of nodes in the ring, and the convergence time is
   independent of the number of nodes in the ring.









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RFC 3619                 Extreme Networks' EAPS             October 2003


2.  Concept of Operation

   An EAPS Domain exists on a single Ethernet ring.  Any Ethernet
   Virtual Local Area Network (VLAN) that is to be protected is
   configured on all ports in the ring for the given EAPS Domain.  Each
   EAPS Domain has a single designated "master node".  All other nodes
   on that ring are referred to as "transit nodes".

   Of course, each node on the ring will have 2 ports connected to the
   ring.  One port of the master node is designated as the "primary
   port" to the ring, while the other port is designated as the
   "secondary port".

   In normal operation, the master node blocks the secondary port for
   all non-control Ethernet frames belonging to the given EAPS Domain,
   thereby avoiding a loop in the ring.  Existing Ethernet switching and
   learning mechanisms operate per existing standards on this ring.
   This is possible because the master node makes the ring appear as
   though there is no loop from the perspective of the Ethernet standard
   algorithms used for switching and learning.  If the master node
   detects a ring fault, it unblocks its secondary port and allows
   Ethernet data frames to pass through that port.  There is a special
   "Control VLAN" that can always pass through all ports in the EAPS
   Domain, including the secondary port of the master node.

   EAPS uses both a polling mechanism and an alert mechanism, described
   below, to verify the connectivity of the ring and quickly detect any
   faults.

2.1.  Link Down Alert

   When a transit node detects a link-down on any of its ports in the
   EAPS Domain, that transit node immediately sends a "link down"
   control frame on the Control VLAN to the master node.

   When the master node receives this "link down" control frame, the
   master node moves from the "normal" state to the ring-fault state and
   unblocks its secondary port.  The master node also flushes its
   bridging table, and the master node also sends a control frame to all
   other ring nodes, instructing them to flush their bridging tables as
   well.  Immediately after flushing its bridging table, each node
   begins learning the new topology.









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2.2.  Ring Polling

   The master node sends a health-check frame on the Control VLAN at a
   user-configurable interval.  If the ring is complete, the health-
   check frame will be received on its secondary port, where the master
   node will reset its fail-period timer and continue normal operation.

   If the master node does not receive the health-check frame before the
   fail-period timer expires, the master node moves from the normal
   state to the "ring-fault" state and unblocks its secondary port.  The
   master node also flushes its bridging table and sends a control frame
   to all other nodes, instructing them to also flush their bridging
   tables.  Immediately after flushing its bridge table, each node
   starts learning the new topology.  This ring polling mechanism
   provides a backup in the event that the Link Down Alert frame should
   get lost for some unforeseen reason.

2.3.  Ring Restoration

   The master node continues sending periodic health-check frames out
   its primary port even when operating in the ring-fault state.  Once
   the ring is restored, the next health-check frame will be received on
   the master node's secondary port.  This will cause the master node to
   transition back to the normal state, logically block non-control
   frames on the secondary port, flush its own bridge table, and send a
   control frame to the transit nodes, instructing them to flush their
   bridging tables and re-learn the topology.

   During the time between the transit node detecting that its link is
   restored and the master node detecting that the ring is restored, the
   secondary port of the master node is still open -- creating the
   possibility of a temporary loop in the topology.  To prevent this,
   the transit node will place all the protected VLANs transiting the
   newly restored port into a temporary blocked state, remember which
   port has been temporarily blocked, and transition into the "pre-
   forwarding" state.  When the transit node in the "pre-forwarding"
   state receives a control frame instructing it to flush its bridging
   table, it will flush the bridging table, unblock the previously
   blocked protected VLANs on the newly restored port, and transition to
   the "normal" state.











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3.  Multiple EAPS Domains

   An EAPS-enabled switch can be part of more than one ring.  Hence, an
   EAPS-enabled switch can belong to more than one EAPS Domain at the
   same time.  Each EAPS Domain on a switch requires a separate instance
   of the EAPS protocol on that same switch, one instance per EAPS-
   protected ring.

   One can also have more than one EAPS domain running on the same ring
   at the same time.  Each EAPS Domain has its own unique master node
   and its own set of protected VLANs.  This facilitates spatial reuse
   of the ring's bandwidth.

   EAPS Frame Format

         0         1          2          3          4        4
         12345678 90123456 78901234 56789012 34567890 12345678
        +--------+--------+--------+--------+--------+--------+
        |         Destination MAC Address (6 bytes)           |
        +--------+--------+--------+--------+--------+--------+
        |         Source MAC Address (6 bytes)                |
        +--------+--------+--------+--------+--------+--------+
        |    EtherType    |PRI | VLAN ID    |  Frame Length   |
        +--------+--------+--------+--------+--------+--------+
        |    DSAP/SSAP    | CONTROL|     OUI = 0x00E02B       |
        +--------+--------+--------+--------+--------+--------+
        |     0x00bb      |  0x99  |  0x0b  |  EAPS_LENGTH    |
        +--------+--------+--------+--------+--------+--------+
        |EAPS_VER|EAPSTYPE|  CTRL_VLAN_ID   |    0x0000       |
        +--------+--------+--------+--------+--------+--------+
        |  0x0000         |    SYSTEM_MAC_ADDR (6 bytes)      |
        +--------+--------+--------+--------+--------+--------+
        |                 |   HELLO_TIMER   |    FAIL_TIMER   |
        +--------+--------+--------+--------+--------+--------+
        | STATE  | 0x00   |   HELLO_SEQ     |     0x0000      |
        +--------+--------+--------+--------+--------+--------+
        |                 RESERVED (0x000000000000)           |
        +--------+--------+--------+--------+--------+--------+
        |                 RESERVED (0x000000000000)           |
        +--------+--------+--------+--------+--------+--------+
        |                 RESERVED (0x000000000000)           |
        +--------+--------+--------+--------+--------+--------+
        |                 RESERVED (0x000000000000)           |
        +--------+--------+--------+--------+--------+--------+
        |                 RESERVED (0x000000000000)           |
        +--------+--------+--------+--------+--------+--------+
        |                 RESERVED (0x000000000000)           |
        +--------+--------+--------+--------+--------+--------+



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RFC 3619                 Extreme Networks' EAPS             October 2003


      Where:

          Destination MAC Address is always 0x00e02b000004.
          PRI contains 3 bits of priority, with 1 other bit reserved.
          EtherType is always 0x8100.
          DSAP/SSAP is always 0xAAAA.
          CONTROL is always 0x03.
          EAPS_LENGTH is 0x40.
          EAPS_VERS is 0x0001.
          CTRL_VLAN_ID is the VLAN ID for the Control VLAN in use.
          SYSTEM_MAC_ADDR is the System MAC Address of the sending node.
          HELLO_TIMER is the value set by the Master Node.
          FAIL_TIMER is the value set by the Master Node.
          HELLO_SEQ is the sequence number of the Hello Frame.

      EAPS Type (EAPSTYPE) values:
          HEALTH              = 5
          RING-UP-FLUSH-FDB   = 6
          RING-DOWN-FLUSH-FDB = 7
          LINK-DOWN           = 8
          All other values are reserved.

      STATE values:
          IDLE           = 0
          COMPLETE       = 1
          FAILED         = 2
          LINKS-UP       = 3
          LINK-DOWN      = 4
          PRE-FORWARDING = 5
          All other values are reserved.

4.  Security Considerations

   Anyone with physical access to the physical layer connections could
   forge any sort of Ethernet frame they wished, including but not
   limited to Bridge frames or EAPS frames.  Such forgeries could be
   used to disrupt an Ethernet network in various ways, including
   methods that are specific to EAPS or other unrelated methods, such as
   forged Ethernet bridge frames.

   As such, it is recommended that users not deploy Ethernet without
   some form of encryption in environments where such active attacks are
   considered a significant operational risk.  IEEE standards already
   exist for link-layer encryption.  Those IEEE standards could be used
   to protect an Ethernet's links.  Alternately, upper-layer security
   mechanisms could be used if it is more appropriate to the local
   threat model.




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RFC 3619                 Extreme Networks' EAPS             October 2003


5.  Intellectual Property Rights Notice

   The IETF has been notified of intellectual property rights claimed in
   regard to some or all of the specification contained in this
   document.  For more information, consult the online list of claimed
   rights.

6.  Acknowledgement

   This document was edited together and put into RFC format by R.J.
   Atkinson from internal documents created by the authors below.  The
   Editor is solely responsible for any errors made during redaction.

7.  Editor's Address

   R. Atkinson
   Extreme Networks
   3585 Monroe Street
   Santa Clara, CA, 95051 USA

   Phone: +1 (408)579-2800
   EMail: rja@extremenetworks.com

8.  Authors' Addresses

   S. Shah
   Extreme Networks
   3585 Monroe Street
   Santa Clara, CA, 95051

   Phone: +1 (408)579-2800
   EMail: sshah@extremenetworks.com


   M. Yip
   Extreme Networks
   3585 Monroe Street
   Santa Clara, CA, 95051

   Phone: +1 (408)579-2800
   EMail: my@extremenetworks.com










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RFC 3619                 Extreme Networks' EAPS             October 2003


9.  Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assignees.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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