Cabletron's VlanHello Protocol Specification Version 4
RFC 2641

Document Type RFC - Informational (August 1999; No errata)
Last updated 2013-03-02
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Network Working Group                                           D. Hamilton
Request for Comments: 2641                                        D. Ruffen
Category: Informational                      Cabletron Systems Incorporated
                                                                August 1999

              Cabletron's VlanHello Protocol Specification
                               Version 4

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 (1999).  All Rights Reserved.

Abstract

   The VlanHello protocol is part of the InterSwitch Message Protocol
   (ISMP) which provides interswitch communication between switches
   running Cabletron's SecureFast VLAN (SFVLAN) product.  Switches use
   the VlanHello protocol to discover their neighboring switches and
   establish the topology of the switch fabric.

Table of Contents

   1. Introduction......................................  2
      1.1 Data Conventions..............................  2
   2. VlanHello Protocol Operational Overview...........  2
      2.1 Neighbor Discovery............................  2
      2.2 Port States...................................  3
      2.3 Topology Events...............................  5
      2.4 Timers........................................  9
   3. InterSwitch Message Protocol......................  9
      3.1 Frame Header.................................. 10
      3.2 ISMP Packet Header............................ 11
      3.3 ISMP Message Body............................. 12
   4. Interswitch Keepalive Message..................... 13
   5. Security Considerations........................... 16
   6. References........................................ 16
   7. Authors' Addresses................................ 16
   8. Full Copyright Statement.......................... 17

Hamilton & Ruffen            Informational                      [Page 1]
RFC 2641       Cabletron's VlanHello Protocol Version 4      August 1999

1. Introduction

   This memo is being distributed to members of the Internet community
   in order to solicit reactions to the proposals contained herein.
   While the specification discussed here may not be directly relevant
   to the research problems of the Internet, it may be of interest to
   researchers and implementers.

1.1 Data Conventions

   The methods used in this memo to describe and picture data adhere to
   the standards of Internet Protocol documentation [RFC1700], in
   particular:

      The convention in the documentation of Internet Protocols is to
      express numbers in decimal and to picture data in "big-endian"
      order.  That is, fields are described left to right, with the most
      significant octet on the left and the least significant octet on
      the right.

      The order of transmission of the header and data described in this
      document is resolved to the octet level.  Whenever a diagram shows
      a group of octets, the order of transmission of those octets is
      the normal order in which they are read in English.

      Whenever an octet represents a numeric quantity the left most bit
      in the diagram is the high order or most significant bit.  That
      is, the bit labeled 0 is the most significant bit.

      Similarly, whenever a multi-octet field represents a numeric
      quantity the left most bit of the whole field is the most
      significant bit.  When a multi-octet quantity is transmitted the
      most significant octet is transmitted first.

2. VlanHello Protocol Operational Overview

   Switches use the VlanHello protocol to detect their neighboring
   switches and establish the topology of the switch fabric.

2.1 Neighbor Discovery

   At initialization, each switch sends an Interswitch Keepalive message
   out all local ports except those which have been preconfigured such
   that they cannot be Network ports (see Section 2.2).  Then, as each
   switch discovers its neighboring switches via incoming Interswitch
   Keepalive messages, it notifies its local topology services (see
   Section 2.3), which then build the topology tables for the switching
   fabric.

Hamilton & Ruffen            Informational                      [Page 2]
RFC 2641       Cabletron's VlanHello Protocol Version 4      August 1999

   Each switch continues to send Interswitch Keepalive messages at
   regular intervals (currently 5 seconds).  If a switch has not heard
   from one of its neighbors for some predetermined interval (see
   Section 2.4), notification is sent to all interested services and the
   neighboring switch is removed from the topology table.

   Interswitch Keepalive messages are described in Section 4.

2.2 Port States

   Each port on a switch can be in one of several different states.
   These states are listed below.  Figure 1 shows how the port state
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