Enterasys Networks X-PeditionTM manual How Triggered-on-Demand RIP Works

IP Routing Protocols

•Offset metric parameters - route metrics via RIP. Adding an offset to an interface might force a route through that interface to become a backup route

•Route filtering, in association with access lists, is enabled by the distribute-listcommand

•RIP timers can be set for update, invalid and flush intervals with the timers basic command

•Statistical display commands revealing RIP counters including show ip traffic, show ip route, show ip protocols

Triggered-on-Demand RIP

Triggered-on-demand RIP (defined in RFC-2091) is available for sending routing updates on a

PPPserial (WAN) port only. This feature updates the XSR’s RIP routing table only when the topology changes or when a next hop’s reachability is detected on the WAN side of the link.

This functionality reduces the on-demand WAN circuit’s routing traffic letting the link be brought down when application traffic ceases. Regular RIP updates would prevent the connection from being torn down when application use ends. The following conditions govern the feature’s use:

•RIP must be enabled

•IP split horizon must be enabled (default). Whether poison is enabled or not, triggered on demand will still send its updates with poison

Triggered-on-demand RIP on the XSR is implemented by this command:

•ip rip triggered-on-demandenables the functionality on a per interface basis. Be aware that this command runs on point-to-point Serial interfaces only.

Note: The ip rip disable-triggered-updatescommand, with the default enforced (triggered updates enabled), invokes triggered updates in a timely fashion.

Related commands include:

•ip rip max-retransmissionssets the number of retransmissions to be sent.

•ip rip polling-intervalsets the polling period for triggered RIP requests. Refer to the XSR CLI Reference Guide for more information on commands.

How Triggered-on-Demand RIP Works

To better understand when to configure triggered-on-demand RIP, consider how it works. Routing updates are sent on the WAN in the following manner:

•The full content of the routing database is sent when:

–An update request is received. An update is sent only to the neighbor requesting it.

–The XSR is first powered up. An update is sent through all interfaces running triggered- on-demand RIP.

–An interface is brought up. An update is sent only out the interface which was brought up.

•A partial update of the database is sent when:

–An interface is brought up. The new local route is advertised to all other interfaces running triggered-on-demand RIP.

–An interface is brought down. All routes reachable through the interface that went down are advertised as unreachable to the other interfaces running triggered-on-demand RIP.

5-12 Configuring IP