Enterasys Networks 2200 - Manual (Page 315)

GARP Switch Operation
Generic Attribute Registration Protocol (GARP) A-3
A.1.2 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 wish to 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
Chapter 12 .
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.