GARP Multicast Registration Protocol (GMRP)Local Management Supplement4-3Configuring 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 themember list if the end station A is removed. This ensures that if switchesare disconnected, or if end stations are removed, the registeredinformation remains accurate.The end result is that the Port VLAN List of a port is updated withinformation about VLANs that reside off that port, even if the actualstation on the VLAN is several hops away.4.2 GARP MULTICAST REGISTRATION PROTOCOL(GMRP)GMRP functions in a similar fashion as GVRP, except that GMRPregisters multicast addresses on ports. The GMRP uses the multicastaddress (01-80-C2-00-00-20) for controlling the flooding of multicastframes. End stations register with the port that they are connected to andtell the port which multicast frames they will receive. This isaccomplished under control of GMRP, which is propagated in VLANcontext.More Detail on Received GMRP FramesThe device is capable of supporting multiple filter databases and eachVLAN is assigned to a database. When GMRP frames are received, theymay contain a tag or be untagged.If the GMRP frame is untagged, the multicast addresses listed in theGMRP frame are added to the Port VLAN List of the receiving port. (Formore information about the Port VLAN List, refer to the CabletronSystems 802.1Q VLAN Users Guide.)If the GMRP frame is tagged, then the VLAN ID in the tag is used to findthe filter database to which the multicast address is registered, and thenthe frame is transmitted out the appropriate ports accordingly.
