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GVRP: GARP VLAN Registration Protocol

March 23rd, 2010

TheĀ  GARP (Generic Attribute Registration Protocol) VLAN Registration Protocol (GVRP) defines a GARP application that provides the 802.1Q-compliantVLAN pruning and dynamic VLAN creation on 802.1Q trunk ports. GVRP is an application defined in the IEEE 802.1P standard that allows for the control of 802.1Q VLANs.

With GVRP, the switch can exchange VLAN configuration information with other GVRP switches, prune unnecessary broadcast and unknown unicast traffic, and dynamically create and manage VLANs on switches connected through 802.1Q trunk ports.

GVRP makes use of GID and GIP, which provide the common state machine descriptions and the common information propagation mechanisms defined for use in GARP-based applications. GVRP runs only on 802.1Q trunk links. GVRP prunes trunk links so that only active VLANs will be sent across trunk connections. GVRP expects to hear join messages from the switches before it will add a VLAN to the trunk. GVRP updates and hold timers can be altered. GVRP ports run in various modes to control how they will prune VLANs. GVRP can be configured to dynamically add and manage VLANS to the VLAN database for trunking purposes.

In other words, GVRP allows the propagation of VLAN information from device to device. With GVRP, a single switch is manually configured with all the desired VLANs for the network, and all other switches on the network learn those VLANs dynamically. An endnode can be plugged into any switch and be connected to that endnode’s desired VLAN. For endnodes to make use of GVRP, they need GVRP-aware Network Interface Cards (NICs). The GVRP-aware NIC is configured with the desired VLAN or VLANs, then connected to a GVRP-enabled switch. The NIC communicates with the switch, and VLAN connectivity is established between the NIC and switch.

Protocol Structure – GVRP: GARP VLAN Registration Protocol

GVRP messages have the same structure as GARP where the attribute type is specific to GVRP: 1 VID Group Attribute Type.

GARP PDU structure

GVRP Frame Format

* Protocol ID – Identifies the GARP protocol.
* Identifier – Decimal value which aids in matching requests and 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 can be:
o 0 – Leave_all
o 1 – Join_Empty operator
o 2 – Join_In operator
o 3 – Leave_Empty operator
o 4 – Leave_In operator
o 5 – Empty operator
* Attribute value – This is encoded in accordance with the specification for the Attribute Type. In case of GVRP, it has two bytes with the VLAN ID value.
* End mark – Coded as 0.

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