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GARP Multicast Registration Protocol (GMRP)
Local Management Supplement 4-3
Configuring a VLAN on an 802.1Q switch creates a static GVRP entry.
The entry will always remain registered and will not time out. However,
dynamic entries will time-out and their registrations are removed from the
member list if the end station A is removed. This ensures that if switches
are disconnected, or if end stations are removed, the registered
information remains accurate.
The end result is that the Port VLAN List of a port is updated with
information about VLANs that reside off that port, even if the actual
station on the VLAN is several hops away.
4.2 GARP MULTICAST REGISTRATION PROTOCOL
(GMRP)
GMRP functions in a similar fashion as GVRP, except that GMRP
registers multicast addresses on ports. The GMRP uses the multicast
address (01-80-C2-00-00-20) for controlling the flooding of multicast
frames. End stations register with the port that they are connected to and
tell the port which multicast frames they will receive. This is
accomplished under control of GMRP, which is propagated in VLAN
context.
More Detail on Received GMRP Frames
The device is capable of supporting multiple filter databases and each
VLAN is assigned to a database. When GMRP frames are received, they
may contain a tag or be untagged.
If the GMRP frame is untagged, the multicast addresses listed in the
GMRP frame are added to the Port VLAN List of the receiving port. (For
more information about the Port VLAN List, refer to the Cabletron
Systems 802.1Q VLAN Users Guide.)
If the GMRP frame is tagged, then the VLAN ID in the tag is used to find
the filter database to which the multicast address is registered, and then
the frame is transmitted out the appropriate ports accordingly.