Qtech QSW-2900-24T4-AC [77/209] 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

4-75

GARP itself does not exist on a device as an entity. GARP-compliant application entities are called GARP

applications. One example is GVRP. When a GARP application entity is present on a port on your device, this port is

regarded a GARP application entity.

a) GARP messages and timers

1) GARP messages

GARP participants exchange attributes primarily by sending the following three types of messages:

· Join to announce the willingness to register some attribute with other participants.

· Leave to announce the willingness to deregister with other participants. Together with Join

messages, Leave messages help GARP participants complete attribute reregistration and

deregistration.

· LeaveAll to deregister all attributes. A LeaveAll message is sent upon expiration of a LeaveAll

timer, which starts upon the startup of a GARP application entity.

· Through message exchange, all attribute information that needs registration propagates to all

GARP participants throughout a bridged LAN.

2) GARP timers

GARP sets interval for sending GARP messages by using these four timers:

· Hold timer –– When a GARP application entity receives the first registration request, it starts a

hold timer and collects succeeding requests. When the timer expires, the entity sends all these requests in

one Join message. This can thus help you save bandwidth.

· Join timer –– Each GARP application entity sends a Join message twice for reliability sake and

uses a join timer to set the sending interval.

· Leave timer –– Starts upon receipt of a Leave message sent for deregistering some attribute

information. If no Join message is received before this timer expires, the GARP application entity removes

the attribute information as requested.

· LeaveAll timer –– Starts when a GARP application entity starts. When this timer expires, the

entity sends a LeaveAll message so that other entities can re-register its attribute information. Then, a

LeaveAll timer starts again.

& Note:

· 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.

b) Operating mechanism of GARP

The GARP mechanism allows the configuration of a GARP participant to propagate throughout a LAN

quickly. In GARP, a GARP participant registers or deregisters its attributes with other participants by making or

withdrawing declarations of attributes and at the same time, based on received declarations or withdrawals handles

attributes of other participants.

GARP application entities send protocol data units (PDU) with a particular multicast MAC address as

destination. Based on this address, a device can identify to which GVRP application, GVRP for example, should a

GARP PDU be delivered.