The information exchange between GARP entities is completed by messages. GARP defines
the messages into three types: Join, Leave and LeaveAll.
•
Join Message:
When a GARP entity expects other switches to register certain attribute
information of its own, it sends out a Join message. And when receiving the Join message
from the other entity or configuring some attributes statically, the device also sends out a
Join message in order to be registered by the other GARP entities.
•
Leave Message:
When a GARP entity expects other switches to deregister certain attribute
information of its own, it sends out a Leave message. And when receiving the Leave
message from the other entity or deregistering some attributes statically, the device also
sends out a Leave message.
•
LeaveAll Message:
Once a GARP entity starts up, it starts the LeaveAll timer. After the timer
times out, the GARP entity sends out a LeaveAll message. LeaveAll message is to
deregister all the attribute information so as to enable the other GARP entities to re-register
attribute information of their own.
Through message exchange, all the attribute information to be registered can be propagated
to all the switches in the same switched network.
The interval of GARP messages is controlled by timers. GARP defines the following timers:
•
Hold Timer:
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, puts all registration information it receives before the timer times out into
one Join message and sends out the message after the timer times out.
•
Join Timer:
To transmit the Join messages reliably to other entities, a GARP entity sends
each Join message two times. The Join timer is used to define the interval between the two
sending operations of each Join message.
•
Leave Timer:
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 Timer:
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.
GVRP
GVRP, as an implementation of GARP, maintains dynamic VLAN registration information and
propagates the information to other switches by adopting the same mechanism of GARP.
After the GVRP feature is enabled on a switch, the switch receives the VLAN registration
information from other switches to dynamically update the local VLAN registration information,
including VLAN members, ports through which the VLAN members can be reached, and so on.
The switch also propagates the local VLAN registration information to other switches so that all
the switching devices in the same switched network can have the same VLAN information. The
VLAN registration information includes not only the static registration information configured
locally, but also the dynamic registration information, which is received from other switches.
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