3Com WX3000 operation manual Operating mechanism of Garp, Garp message format

Leave messages, LeaveAll messages, together with Join messages ensure attribute information can be deregistered and re-registered.

Through message exchange, all the attribute information to be registered can be propagated to all the GARP-enabled switches in the same LAN.

2)GARP timers

Timers determine the intervals of sending different types of GARP messages. GARP defines four timers to control the period of sending GARP messages.

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Hold: When a GARP entity receives a piece of registration information, it does not send out a Join message immediately. Instead, to save the bandwidth resources, it starts the Hold timer and puts all received registration information before the timer times out into one Join message and sends out the message after the timer times out.

Join: To make sure the devices can receive Join messages, each Join message is sent twice. If the first Join message sent is not responded for a specific period, a second one is sent. The period is determined by this timer.

Leave: When a GARP entity expects to deregister a piece of attribute information, it sends out a Leave message. Any GARP entity receiving this message starts its Leave timer, and deregisters the attribute information if it does not receives a Join message again before the timer times out.

LeaveAll: Once a GARP entity starts up, it starts the LeaveAll timer, and sends out a LeaveALL message after the timer times out, so that other GARP entities can re-register all the attribute information on this entity. After that, the entity restarts the LeaveAll timer to begin a new cycle.

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The settings of GARP timers apply to all GARP applications, such as GVRP, on a LAN.

Unlike other three timers, which are set on a port basis, the LeaveAll timer is set in system view and takes effect globally.

A GARP application entity may send LeaveAll messages at the interval set by its LeaveAll timer or the LeaveAll timer on another device on the network, whichever is smaller. This is because each time a device on the network receives a LeaveAll message it resets its LeaveAll timer.

Operating mechanism of GARP

Through the mechanism of GARP, the configuration information on a GARP member will be propagated within the whole LAN. A GARP member can be a terminal workstation or a bridge; it instructs other GARP members to register/deregister its attribute information by declaration/recant, and register/deregister other GARP member's attribute information according to other member's declaration/recant. When a port receives an attribute declaration, the port will register this attribute. When a port receives an attribute recant, the port will deregister this attribute.

The protocol packets of GARP entities use specific multicast MAC addresses as their destination MAC addresses. When receiving these packets, the switch distinguishes them by their destination MAC addresses and delivers them to different GARP application (for example, GVRP) for further processing.

GARP message format

The GARP packets are in the following format:

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