3Com Switch 4500 26-Port Configuration Manual page 116

114 C 6: IP R
HAPTER OUTING
P O
ROTOCOL PERATION
By default, the interface receives and sends the RIP-1 packets. It transmits packets
in multicast mode when the interface RIP version is set to RIP-2.
Configuring RIP Timers
As stipulated in RFC1058, RIP is controlled by three timers: period update,
timeout, and garbage-collection:
Period update is triggered periodically to send all RIP routes to all neighbors.
■
If an RIP route has not been updated when the timeout timer expires, the route
■
is considered unreachable.
If the garbage-collection timer expires before the unreachable route is updated
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by the update packets from the neighbors, the route will be deleted completely
from the routing table.
Modification of these timers can affect the convergence speed of RIP.
Perform the following configuration in RIP View.
Table 108 Configuring RIP timers
Operation
Configure RIP timers
Restore the default settings of RIP
The modification of RIP timers is validated immediately.
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.
Command
timers { update update_timer_length |
timeout timeout_timer_length } *
undo timers { update | timeout } *