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228 CHAPTER 16: IP ROUTING PROTOCOL OPERATION
By default, the values of the period update and timeout timers are 30 seconds and
180 seconds respectively. The value of the garbage-collection timer is four times of
that of Period Update timer: 120 seconds.
In fact, you may find that the timeout time of the garbage-collection timer is not
fixed. If the period update timer is set to 30 seconds, the garbage-collection timer
might range from 90 to 120 seconds.
Before RIP completely deletes an unreachable route from the routing table, it
advertises the route by sending four update packets with a route metric of 16, to let
all the neighbors know that the route is unreachable. Routes do not always become
unreachable when a new period starts so the actual value of the garbage-collection
timer is 3 to 4 times of that of the period update timer.
You must consider network performance when adjusting RIP timers, and configure all
the routes that are running RIP, so as to avoid unnecessary traffic or network
oscillation.
Configuring RIP-1 Zero Field Check of the Interface Packet
According to the RFC1058, some fields in the RIP-1 packet must be 0. When an
interface version is set to RIP-1, the zero field check must be performed on the
packet. If the value in the zero field is not zero, processing is refused. There are no
zero fields in RIP-2 packets so configuring a zero field check is invalid for RIP-2.
Perform the following configurations in RIP View.
Specifying the Operating State of the Interface
In the Interface View, you can specify whether RIP update packets are sent and
received on the interface. In addition, you can specify whether an interface sends or
receives RIP update packets.
Perform the following configuration in Interface View:
The
undo rip work command and the undo network command have similar but not
the same functions. The
undo rip work command allows other interfaces to forward
the route of the interface applying this command. The
undo network command
prevents other interfaces from forwarding the route of the interface applying this
command, and it appears that this interface has been removed.
Table 207 Configuring Zero Field Check of the Interface Packets
Operation Command
Configure zero field check on the RIP-1 packet checkzero
Disable zero field check on the RIP-1 packet undo checkzero
Table 208 Specifying the Operating State of the Interface
Operation Command
Enable the interface to run RIP rip work
Disable the interface from running RIP undo rip work
Enable the interface to receive RIP update packets rip input
Disable the interface from receiving RIP update packets undo rip input
Enable the interface to send RIP update packets rip output
Disable the interface from sending RIP update packets undo rip output