Cisco Systems 78-11741-02 Changing the Routing Level for an Area, Sets the overload bit, IPC-286

Configuring Integrated IS-IS

Miscellaneous IS-IS Parameters Configuration Task List

Unless you specify the on-startupkeyword, this command sets the overload bit immediately and it remains set until the no set-overload-bitcommand is specified. If you specify the on-startupkeyword, you must indicate whether it is set for a specified number of seconds or until BGP has converged. If BGP does not signal IS-IS that it has converged, IS-IS will turn off the overload bit after 10 minutes.

In addition to setting the overload bit, you might also want to suppress certain types of IP prefix advertisements from LSPs. For example, allowing IP prefix propagation between Level1 and Level 2 effectively makes a node a transit node for IP traffic, which may be undesirable. The suppress keyword used with the interlevel or external keyword (or both) accomplishes that suppression while the overload bit is set.

To set the overload bit, use the following command in router configuration mode:

Command	Purpose
Router(config-router)# set-overload-bit	Sets the overload bit.
[on-startup {seconds wait-for-bgp}]
[suppress {[interlevel] [external]}]

Changing the Routing Level for an Area

You can change the routing level configured for an area using the is-typerouter configuration command. If the router instance has been configured for a Level 1-2 area (the default for the first instance of the IS-IS routing process in a Cisco router), you can remove Level 2 (interarea) routing for the area using the is-typecommand and change the routing level to Level 1 (intra-area). You can also configure Level 2 routing for an area using the is-typecommand, but the instance of the IS-IS router configured for Level 2 on the Cisco router must be the only instance configured for Level 2.

To change the routing level for an IS-IS routing process in a given area, use the following command in router configuration mode:

Command	Purpose
Router (config)# is-type {level-1 level-1-2	Configures the routing level for an instance of the IS-IS routing
level-2-only}	process.

Tuning LSP Interval and Lifetime

By default, the router sends a periodic LSP refresh every 15 minutes. LSPs remain in a database for

20 minutes by default. If they are not refreshed by that time, they are deleted. You can change the LSP refresh interval or the LSP lifetime. The LSP interval should be less than the LSP lifetime or else LSPs will time out before they are refreshed. The software will adjust the LSP refresh interval if necessary to prevent the LSPs from timing out.

Cisco IOS IP Configuration Guide

IPC-286