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How to configure the GARP timer on Catalyst switches running CatOS

Core issue

The purpose of the Generic Attribute Registration Protocol (GARP) is to provide generic framework where devices in a bridged LAN (end stations and switches) can register and de-register attribute values, such as VLAN Identifiers, with each other. 

GARP is not directly used by devices in a bridged LAN. The applications of GARP specify what the attribute represent and perform the meaningful actions. The GARP VLAN Registration Protocol (GVRP) application distributes dynamic filter entries for VLAN membership among the forwarding databases of VLAN-aware switches.

To use GARP, a GARP application has to be created. The Layer 3 (L3) switch has one GARP application: the GVRP. The purpose of GVRP is to propagate VLAN information between VLAN-aware    switches. GVRP creates dynamic VLANs when GARP is enabled on the switch. Timers    are used in the state machines to generate events and control state transitions.

Resolution

You can modify the default GARP timer values on the switch.

To set the GARP timer values, issue the set garp timer {join | leave | leaveall} timer_value command in privileged mode.

When setting the timer values, the value for leave must be greater than three times the join value (leave >= join * 3). The value for leaveall must be greater than the value for leave (leaveall > leave). If you attempt to set a timer value that does not adhere to these rules, an error is returned.

For example, if you set the leave timer to 600 ms, and you attempt to configure the join timer to 350 ms, an error is returned. Set the leave timer to at least 1050 ms, and set the join timer to 350 ms.

Note: Modifying the GARP timer values affects the behavior of all GARP applications running on the switch, not just GVRP. Set the same GARP timer values on all Layer 2 (L2)-connected devices. If the GARP timers are set differently on L2-connected devices, GARP applications (for example, GMRP and GVRP) do not operate successfully.

To verify the configuration, issue the show garp timer command.


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‎06-18-2009 04:03 PM
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