Enterasys Networks Security Router X-PeditionTM - Manual (Page 114)

IP Routing Protocols
5-12 Configuring IP
• 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-list command
• 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
PPP serial (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-demand enables the functionality on a per interface basis. Be aware
that this command runs on point-to-point Serial interfaces only.
Related commands include:
• ip rip max-retransmissions sets the number of retransmissions to be sent.
• ip rip polling-interval sets 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.
Note: The ip rip disable-triggered-updates command, with the default enforced (triggered updates
enabled), invokes triggered updates in a timely fashion.