3Com Switch 8800 Advanced Software V5 Configuration Guide

140 CHAPTER 12: GVRP CONFIGURATION
■ Leave to deregister some attribute 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 the LeaveAll timer, which starts upon the startup of a GARP application
entity.
Through message exchange, all attribute information to be registered propagates
to all GARP participants throughout the LAN.
2 GARP timers
There are four GARP timers:
■ Hold timer - When a GARP application entity receives the first registration
request, it starts the Hold timer and collects succeeding requests. When the
timer expires, the entity sends all these requests in one Join message, thus
saving bandwidth.
■ Join timer -- A GARP application entity sends each Join message twice for
reliability sake and uses the Join timer to set the interval between the two
sending operations.
■ Leave timer -- Starts upon receipt of a Leave message from another GARP
application entity 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 all its attribute information, and, at the same time, it restarts the
LeaveAll timer.
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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 on all ports.
■ Different devices on a network may have different LeaveAll timer values. Each
time a device on the network receives a LeaveAll message, it resets its LeaveAll
timer. Therefore, each GARP application entity will send LeaveAll messages
based on the shortest LeaveAll timer in the network. As a result, only the
shortest LeaveAll timer in the network will take effect.
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.