network protocols handbook.pdf

209Protocols GuideLAN - Virtual LAN ProtocolsProtocol NameGVRP: GARP VLAN RegistrationProtocolProtocol DescriptionThe GARP (Generic Attribute Registration Protocol) VLANRegistration Protocol (GVRP) defines a GARP application thatprovides 802.1Q-compliant VLAN pruning and dynamic VLANcreation on 802.1Q trunk ports. GVRP is an application, definedin the IEEE 802.1P standard, which allows for the control of802.1Q VLANs.With GVRP, the switch can exchange VLAN configuration informationwith other GVRP switches, prune unnecessary broadcastand unknown unicast traffic, and dynamically create andmanage VLANs on switches connected through 802.1Q trunkports.GVRP makes use of GID and GIP, which provide the commonstate machine descriptions and the common information propagationmechanisms defined for use in GARP-based applications.GVRP runs only on 802.1Q trunk links. GVRP prunes trunk linksso that only active VLANs will be sent across trunk connections.GVRP expects to hear join messages from the switches beforeit will add a VLAN to the trunk. GVRP updates and hold timerscan be altered. GVRP ports run in various modes to control howthey will prune VLANs. GVRP can be configured to dynamicallyadd and manage VLANS to the VLAN database for trunking purposes.In other words, GVRP allows the propagation of VLAN informationfrom device to device. With GVRP, a single switch is manuallyconfigured with all the desired VLANs for the network, andall other switches on the network learn those VLANs dynamically.An endnode can be plugged into any switch and be connectedto that endnode’s desired VLAN. For endnodes to makeuse of GVRP, they need GVRP-aware Network Interface Cards(NICs). The GVRP-aware NIC is configured with the desiredVLAN or VLANs, then connected to a GVRP-enabled switch.The NIC communicates with the switch, and VLAN connectivityis established between the NIC and switch.Protocol StructureGVRP messages have the same structure as GARP with the attributetype pecific to GVRP: 1 VID Group Attribute Type.GARP message structure1 byteAttributeAttribute 1 ... Attribute n End marktypeGARP attribute structure1 byte 1 byte 1 byteAttribute length Attribute event Attribute value• Protocol ID - Identifies the GARP protocol.• Identifier - Decimal value which aids in matching requestsand replies.• Attribute type - Defines the attribute. Values may be:1 Group attribute; 2 Service Requirement attribute.• Attribute length - Length of the Attribute.• Attribute event - The values of the attribute event canbe:0 Leave_all1 Join_Empty operator2 Join_In operator3 Leave_Empty operator4 Leave_In operator5 Empty operator• Attribute value - This is encoded in accordance withthe specification for the Attribute Type.• End mark - Coded as 0.Related protocolsIEEE 802.1D, 802.1Q, 802.1P, GMRP, GARPSponsor SourceGVRP standard is defined by IEEE (http://www.ieee.org) 802.1Qand 802.1P.Referencehttp://standards.ieee.org/getieee802/download/802.1Q-1998.pdfIEEE 802.1Q Standardhttp://www.alliedtelesyn.co.nz/documentation/at8700/261/pdf/garp.pdfOverview of Generic Attribute Registration ProtocolGARP PDU Format:2 bytesProtocol IDMessage