AT-S63 Management Software Features Guide
Section VI: Virtual LANs 291
Generic Attribute Registration Protocol (GARP) Overview
The following is a technical overview of GARP. An understanding of GARP
may prove helpful when you use GVRP.
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 deregister 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 Layer 2 switch
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 deregistration 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 GARP Information
Propagation (GIP) component propagates information between GARP
participants for the same application in a switch. 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.
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