Allied Telesis AT-S62 - Manual (Page 582)

Chapter 25: GARP VLAN Registration Protocol
582 Section V: VLANs
Basic Overview of GARP VLAN Registration Protocol (GVRP)
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 have to be manually configured in each switch.
This can be 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, an application of the Generic Attribute Registration
Protocol (GARP), can perform this for you automatically.
The AT-S62 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 to 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:
ˆ If a 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.
ˆ If the VLAN already exists on the switch but the port that received the
PDU is not a member, the switch adds the port as a tagged member of
the VLAN. 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. Once 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 shutdown 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 (i.e., user created).