3Com corebuilder 3500 Implementation Manual page 183

GVRP enables your system to advertise its manually configured IEEE
802.1Q VLANs to other devices supporting GVRP. Because the VLANs are
advertised, GVRP-aware devices in the core of the network need no
manual configuration to pass IEEE 802.1Q frames to the proper
destination. The method of VLAN advertisement used by all
GVRP-capable switches involves protocol data units (PDUs), similar to the
method used by STP. GVRP-capable devices send their updates to a
well-known multicast address to which all GVRP-capable devices listen for
information changes.
Enabling GVRP lets the system dynamically adjust active network
topologies in response to configuration changes in one or more VLANs.
GVRP then advertises VLAN changes on each bridge to all other GVRP
bridges in the network.
Important Considerations
To use GVRP, consider the following:
To take advantage of dynamic IEEE 802.1Q VLAN configuration,
enable GVRP as an entire bridge state and then as an individual bridge
port state for the appropriate ports. See Chapter 7. By default, GVRP
is disabled as both a bridge state and a bridge port state. If GVRP is
enabled, the VLAN origin for a port-based VLAN is dynamic (with
GVRP). When GVRP is disabled, the VLAN origin is either static
(traditional static VLAN without GVRP) or router (router port).
In a GVRP environment, devices must be GVRP-enabled (that is,
support GVRP). These devices may be end stations with 3Com's
DynamicAccess ® software or other switches that explicitly
enable GVRP.
VLANs created dynamically with GVRP exist only as long as a
GVRP-enabled device is sending updates. If the devices no longer send
updates, or GVRP is disabled, or the system is rebooted, all dynamic
VLANs are removed.
GVRP updates are not sent out on any blocked STP ports. GVRP
operates only on ports that are in the STP forwarding state. If GVRP is
enabled, a port that changes to the STP forwarding state begins to
participate in GVRP. A port that changes to an STP state other than
forwarding no longer participates in GVRP.
Port-based VLANs 183