H3C Technologies H3C S3100 Series Switches - Manual (Page 133)

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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.
z 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.
z 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.
z 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.
z 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.
z The settings of GARP timers apply to all GARP applications, such as GVRP, on a LAN.
z Unlike other three timers, which are set on a port basis, the LeaveAll timer is set in system view and
takes effect globally.
z 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: