110 CHAPTER 11: GVRP CONFIGURATION
GARP participant sends LeaveAll messages upon the expiration of the LeaveAll
timer, which is triggered when the GARP participant is created.
Join messages, Leave messages, and LeaveAll message make sure the
reregistration and deregistration of GARP attributes are performed in an orderly
way.
Through message exchange, all attribute information that needs registration
propagates to all GARP participants throughout a LAN.
2 GARP timers
The interval of sending of GARP messages is controlled by the following four
timers:
■ Hold timer -- A GARP participant usually does not forwards a received
registration request immediately after it receives a registration request, instead,
it waits for the expiration of the hold timer. That is, a GARP participant sends
Join messages when the hold timer expires. The Join message contains all the
registration information received during the latest Hold timer cycle. Such a
mechanism saves the bandwidth.
■ Join timer -- Each GARP participant sends a Join message twice for reliability
sake and uses a join timer to set the sending interval. If the first Join message is
not acknowledged after the interval defined by the Join timer, the GARP
participant sends the second Join message.
■ 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 participant removes the attribute information as requested.
■ LeaveAll timer -- Starts when a GARP participant starts. When this timer
expires, the entity sends a LeaveAll message so that other participants can
re-register its attribute information. Then, a LeaveAll timer starts again.
n
■ 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 participant 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
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. When a port receives an
attribute declaration, it registers the attribute; when a port receives an attribute
withdrawal, it deregisters the attribute.
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