110Field Description ValueMessageOne or multiple messages, eachcontaining an attribute type and anattribute listN/AEnd mark Indicates the end of a GARP PDU 0x00Attribute type Defined by the GARP application 0x01 for GVRP, indicating theVLAN ID attributeAttribute list Contains one or multiple attributes N/AAttributeConsists of an Attribute Length, anAttribute Event, and an AttributeValueN/AAttribute length Length of an attribute, inclusive of theattribute length field 2 to 255 (in bytes)Attribute event Event described by the attribute• 0x00—LeaveAll event• 0x01—JoinEmpty event• 0x02—JoinIn event• 0x03—LeaveEmpty event• 0x04—LeaveIn event• 0x05—Empty eventAttribute value Attribute valueVLAN ID for GVRPIf the value of the Attribute eventfield is 0x00 (LeaveAll event), theAttribute value field is invalid.The destination MAC addresses of GARP messages are multicast MAC addresses, and vary with GARPapplications. For example, the destination MAC address of GVRP is 01-80-C2-00-00-21. A networkdevice distributes GARP messages to different GARP applications according to the destination MACaddresses carried in GARP messages.GVRPGVRP overviewAs a GARP application, GVRP enables a network device to propagate local VLAN registrationinformation to other participant devices, and to dynamically update the VLAN registration informationfrom other devices to its local database, including active VLAN members and through which port theycan be reached. This makes sure that all GVRP participants on a bridged LAN maintain the same VLANregistration information. The VLAN registration information propagated by GVRP includes both manuallyconfigured local static entries and dynamic entries from other devices.GVRP registration modesVLANs manually created are called static VLANs, and VLANs created by GVRP are called dynamicVLANs. GVRP provides three registration modes on a port, including Normal, Fixed, and Forbidden. Indifferent registration modes, a port handles static and dynamic VLANs differently:• Normal—Allows dynamic creation, registration, and deregistration of VLANs on the trunk port.• Fixed—Allows manual creation and registration of VLANs, prevents VLAN deregistration, andregisters all known VLANs on other ports on the trunk port.
