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Triggered Extensions to RIP

Feature Summary

Platforms

Prerequisites

Supported RFCs

Triggered Extensions to RIP

Feature Summary

Triggered extensions to IP RIP increase efficiency of RIP on point-to-point, serial interfaces.

Routers are used on connection-oriented networks to allow potential connectivity to many remote destinations. Circuits on the WAN are established on demand and are relinquished when the traffic subsides. Depending on the application, the connection between any two sites for user data could be short and relatively infrequent.

There were two problems using RIP to connect to a WAN:

To overcome these limitations, triggered extensions to RIP cause RIP to send information on the WAN only when there has been an update to the routing database. Periodic update packets are suppressed over the interface on which this feature is enabled.

Benefit

RIP routing traffic is reduced on point-to-point, serial interfaces. Therefore, you can save money on an on-demand circuit for which you are charged for usage.

Platforms

This feature is supported on all platforms running Cisco IOS Release 12.0(1)T that include RIP.

Prerequisites

RIP must be enabled for this feature to function. This feature runs on a point-to-point, serial interface only.

Supported RFCs

This feature partially supports RFC 2091, Triggered Extensions to RIP to Support Demand Circuits.

Configuration Tasks

To enable triggered extensions to RIP, use the following commands beginning in global configuration mode:
Command Purpose

interface serial number

Configure a serial interface.

ip rip triggered

Enable triggered extensions to RIP.

To display the contents of the RIP private database, use the following command in EXEC mode:
Command Purpose

show ip rip database [prefix mask]

Display the contents of the RIP private database.

Command Reference

This section documents the following new commands. All other commands used in this feature module can be found in the Cisco IOS 12.0 documentation set.

ip rip triggered

To enable triggered extensions of RIP, use the ip rip triggered interface configuration command. To disable triggered extensions to RIP, use the no form of this command.

ip rip triggered

Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 12.0(1)T.

When triggered extensions to RIP are enabled, routing updates are transmitted on the WAN only if one of the following occurs:

You might want to enable this feature if you are using an on-demand circuit and you are charged for usage time. Fewer routing updates will incur lower usage costs.

Entries in the routing database can be either temporary or semi-permanent. Entries learned from broadcasts on LANs are temporary; they will expire if not periodically refreshed by more broadcasts.

Entries learned from a triggered response on the WAN are semi-permanent; they do not time out like other entries. Certain events can cause these routes to time out, such as the interface going down, or if the outgoing interface is the same as the incoming interface. Neighbor updates of the routes with a metric of 16 (infinity) mean the route is unreachable, and those routes are eventually removed from the routing table.

Example

The following example enables triggered extensions to RIP:

interface serial 0
  ip rip triggered

Related Commands

show ip rip database

show ip rip database

To display the contents of the RIP private database when triggered extensions to RIP are enabled, use the show ip rip database EXEC command.

show ip rip database [prefix mask]

Syntax Description

prefix

(Optional) Display only the route that matches the specified prefix and mask. Otherwise, the entire database is displayed.

mask

(Optional) Display only the route that matches the specified prefix and mask. Otherwise, the entire database is displayed.

Command Mode

EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 12.0(1)T.

The RIP private database is populated only if triggered extensions to RIP are enabled with the ip rip triggered command.

Sample Displays

The following is sample output of the show ip rip database command:

Router# show ip rip database
172.19.0.0/16    auto-summary
172.19.64.0/24    directly connected, Ethernet0
172.19.65.0/24
    [1] via 172.19.70.36, 00:00:17, Serial1
    [2] via 172.19.67.38, 00:00:25, Serial0
172.19.67.0/24    directly connected, Serial0
172.19.67.38/32    directly connected, Serial0
172.19.70.0/24    directly connected, Serial1
172.19.86.0/24
    [1] via 172.19.67.38, 00:00:25, Serial0
    [1] via 172.19.70.36, 00:00:17, Serial1

The following is sample output of the show ip rip database command with a prefix and mask:

Router# show ip rip database 172.19.86.0 255.255.255.0
172.19.86.0/24
    [1] via 172.19.67.38, 00:00:25, Serial0
    [1] via 172.19.70.36, 00:00:14, Serial1

Related Commands

ip rip triggered


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