Manual

Chapter 21: GARP VLAN Registration Protocol
Section V: Virtual LANs 426
Technical Overview of Generic Attribute Registration
Protocol (GARP)
The purpose of the Generic Attribute Registration Protocol (GARP) is to
provide a generic framework whereby devices in a bridged LAN, for
example, end stations and switches, can register and de-register
attribute values, such as VLAN Identifiers, with each other. In doing so,
the attributes are propagated to devices in the bridged LAN, and these
devices form a “reachability” tree that is a subset of an active topology.
For a bridged LAN, the active topology is normally that created and
maintained by the Spanning Tree Protocol (STP).
To use GARP, a GARP application must be defined. The AT-S62
management software has one GARP application presently
implemented, GVRP.
The GARP application specifies what the attribute represents.
GARP defines the architecture, rules of operation, state machines and
variables for the registration and de-registration of attribute values. By
itself, GARP is not directly used by devices in a bridged LAN. It is the
applications of GARP that perform meaningful actions. The use of GVRP
allows dynamic filter entries for VLAN membership to be distributed
among the forwarding databases of VLAN-active switches.
A GARP Participant in a switch or an end station consists of a GARP
Application component, and a GARP Information Declaration (GID)
component associated with each port of the switch. One such GARP
Participant exists per port, per GARP Application. The propagation of
information between GARP Participants for the same Application in a
switch is carried out by the GARP Information Propagation (GIP)
component. Protocol exchanges take place between GARP Participants
by means of LLC Type 1 services, using the group MAC address and PDU
format defined for the GARP Application concerned.
Every instance of a GARP application includes a database to store the
values of the attributes. Within GARP, attributes are mapped to GID
indexes.