Allied Telesis AT-S63 - Manual (Page 472)

Chapter 21: GARP VLAN Registration Protocol
472 Section III: VLANs
GARP VLAN Registration Protocol (GVRP) Overview
The GARP VLAN Registration Protocol (GVRP) allows network devices to
share VLAN information. The main purpose of GVRP is to allow switches
to automatically discover some of the VLAN information that would
otherwise need to be manually configured in each switch. This is helpful
in networks where VLANs span more than one switch. Without GVRP,
you must manually configure your switches to ensure that the various
parts of a VLAN can communicate across the different switches. GVRP,
which is an application of the Generic Attribute Registration Protocol
(GARP), does this for you automatically.
The AT-S63 management software uses GVRP protocol data units (PDUs)
to share VLAN information among GVRP-active devices. The PDUs
contain the VID numbers of the VLANs on the switch. A PDU contains the
VIDs of all the VLANs on the switch, not just the VID of which the
transmitting port is a member.
When a switch receives a GVRP PDU on a port, it examines the PDU to
determine the VIDs of the VLANs on the device that sent it. It then does
the following:
❑ If the VLAN does not exist on the switch, it creates the VLAN and
adds the port as a tagged member to the VLAN. A VLAN created
by GVRP is called a dynamic GVRP VLAN.
❑ If the VLAN already exists on the switch but the port is not a
member of it, the switch adds the port as a tagged member. A
port that has been added by GVRP to a static VLAN (that is a user-
created VLAN) is called a dynamic GVRP port.
You cannot modify a dynamic GVRP VLAN. After it is created, only GVRP
can modify or delete it. A dynamic GVRP VLAN exists only so long as
there are active nodes in the network that belong to the VLAN. If all
nodes of a dynamic GVRP VLAN are shut down and there are no active
links, the VLAN is deleted from the switch.
A dynamic GVRP port in a static VLAN remains a member of the VLAN as
long as there are active VLAN members. If all members of the VLAN
become inactive or there are no active links, GVRP removes the dynamic
port from the VLAN, but does not delete the VLAN if the VLAN is a static
VLAN.