Cisco Systems 78-11741-02 manual Disabling Holddown, Enforcing a Maximum Network Diameter, IPC-218

Configuring IGRP

IGRP Configuration Task List

To adjust the timers, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# timers basic update invalid	Adjusts routing protocol timers.
holddown flush [sleeptime]

Disabling Holddown

When the Cisco IOS software learns that a network is at a greater distance than was previously known, or it learns the network is down, the route to that network is placed in holddown. During the holddown period, the route is advertised, but incoming advertisements about that network from any router other than the one that originally advertised the new metric of the network will be ignored. This mechanism is often used to help avoid routing loops in the network, but has the effect of increasing the topology convergence time.

To disable holddowns with IGRP, use the following command in router configuration mode. All devices in an IGRP autonomous system must be consistent in their use of holddowns.

Command	Purpose
Router(config-router)# no metric holddown	Disables the IGRP holddown period.

Enforcing a Maximum Network Diameter

The Cisco IOS software enforces a maximum diameter to the IGRP network. Routes whose hop counts exceed this diameter are not advertised. The default maximum diameter is 100 hops. The maximum diameter is 255 hops.

To configure the maximum diameter, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# metric maximum-hopshops	Configures the maximum network diameter.

Validating Source IP Addresses

By default, the system validates the source IP addresses of incoming IGRP routing updates. To disable this function, use the following command in router configuration mode:

Command	Purpose
Router(config-router)#no validate-update-source	Disables the checking and validation of the source
	IP address of incoming routing updates.

Cisco IOS IP Configuration Guide

IPC-218