
Configuring Dial Services
4-6 114062 Rev. A
Exceptions for Sending Routing Updates
Routing updates are sent independent of data in the following two cases:
• An IP or IPX interface becomes active for the first time.
When an IP or IPX interface first initializes, the protocol sends routing
updates to every node in the network. If there is no data, the connection
expires in the user-configured Minimum Duration Time.
• The RIP Broadcast Timer (IP) or RIP/SAP Update Interval (IPX) expires.
Each time the Broadcast Timer or Update Interval expires, the protocol can
request to send updates over an active connection. If you enable dial
optimized routing, the value of the timer defaults to a large value so
connections are infrequent. Setting the value of the Broadcast Timer or
Update Interval to a small value would defeat the purpose of dial optimized
routing.
If a connection is made because there is data to send, the router uses this
opportunity to send routing updates. Consequently, these timers reset instead
of expiring. This further reduces the frequency of connections made due to a
request by the protocol.
Maintaining the Routing Table
Although dial optimized routing limits the amount of routing information across
the network, you can maintain the accuracy of the routing tables using the
following methods.
• Set the Hold Down Timer to a higher value than the Broadcast Timer or
Update Interval.
The Holddown Timer specifies how long unusable routes are advertised after
the route is invalid. This ensures that unreachable routes are kept in the
routing table long enough to be broadcast over an active connection.
• Synchronize protocol requests for a connection.
When a connection is active, the router software sends status messages to IP
or IPX, alerting the protocol that it may send routing updates. If the protocol
does not receive this connection message, it will make a separate request for a
connection. This request causes the Minimum Duration Time to reset and the
connection then remains active for the specified minimum time.
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