GVRP

What is GVRP ?

GVRP, short for GARP VLAN Registration Protocol or Generic VLAN Registration Protocol, is a protocol designed to manage virtual local area networks (VLANs) within a larger network infrastructure. It adheres to the IEEE 802.1Q standard, which specifies a method for tagging frames with VLAN data over trunk links. This functionality allows network devices to share VLAN configuration details dynamically.

Based on the Generic Attribute Registration Protocol (GARP) and IEEE 802.1r, GVRP enables end devices and switches within a VLAN to register and deregister attributes like identifiers and addresses. This ensures that each switch and end device maintains an up-to-date record of all reachable devices on the network. Similar to GARP, GVRP minimizes unnecessary traffic by avoiding information transmission to unregistered devices, requiring only one switch to be manually configured while the others update automatically.

In 2007, GVRP was superseded by the Multiple VLAN Registration Protocol, which became part of the IEEE 802.1ak amendment due to GVRP's performance issues, notably prolonged convergence times that could degrade bandwidth. While GVRP remains within the IEEE standard, its future removal is anticipated.

Benefits of Using GVRP

For large networks with many VLAN segments, GVRP helps maintain a clean VLAN configuration on trunk interfaces. Administrators who implement GVRP can realize three key benefits:

• Auto-cleanup: The switch automatically removes unused VLANs, ensuring that only active VLANs are transmitted over 802.1Q trunk links.

• Efficient Configuration: Administrators simply configure a new VLAN on one switch and the system automatically propagates the configuration to all GVRP-participating switches.

• Reduced Broadcast Traffic: GVRP helps reduce bandwidth consumption for network management tasks by minimizing unnecessary broadcast messages.

How GVRP Functions

When multiple switches are interconnected through GVRP-enabled 802.1Q trunk ports, they will begin to exchange VLAN information both statically and dynamically. Switches with pre-configured VLANs will broadcast these configurations to connected switches using GVRP data units, which are specialized management packets used to distribute VLAN information. When a switch learns of a new VLAN, it adds that VLAN to the list of VLAN tags that it can transmit, following the loop avoidance principle and avoiding routing back learned VLAN information through the receiving interface.

Dynamically acquired VLAN information is stored in the switch's memory, which means that a power failure or reboot will result in the loss of this data. However, once communication is restored, the switch will relearn the shared VLAN data, restoring the network to a fully informed state.

Enabling GVRP

The steps and commands to enable GVRP vary by vendor and switch model, but some general similarities exist:

GVRP can be enabled or disabled globally on the switch.

If enabled, each port set to 802.1Q trunk can be configured in one of the following three modes:

• GVRP Enable: Activates GVRP on trunk interfaces to pass static and dynamic VLAN information.

• GVRP Disable: Disables GVRP on the port and ignores any GVRP communication.

• Block GVRP Registration: Drops all dynamically learned VLANs and prevents new VLANs from registering on the trunk port.

Typical application of GVRP

Distributed switch A is connected to access switches B and C over the 802.1Q trunk and has GVRP enabled globally. the administrator configures VLANs 101 and 201 on switch A. Once these VLANs are configured, the GVRP data unit sends the information containing the new VLANs to switches B and C, which then update their VLAN tables to include 101 and 201 as dynamically learned entries. The two access switches then update their VLAN tables to include 101 and 201 as dynamically learned entries.