RFC 2641 (rfc2641) - Page 2 of 17

Cabletron's VlanHello Protocol Specification Version 4

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 [RFC 1700], 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