864 BigIron RX Series Configuration Guide53-1001986-01Globally configuring IS-IS on a device28• Change the default metric.• Add, change, or negate route redistribution parameters.Some IS-IS parameter changes take effect immediately while others do not take full effect until youdisable, then re-enable route redistribution.Globally configuring IS-IS on a deviceThis section describes how to change the global IS-IS parameters. These parameter settings applyto both IS-IS IPv4 and IS-IS IPv6, although IPv6 is currently not supported.Setting the overload bitIf an IS’s resources are overloaded and are preventing the IS from properly performing IS-IS routing,the IS can inform other ISs of this condition by setting the overload bit in LSPDUs sent to other ISsfrom 0 (off) to 1 (on).When an IS is overloaded, other ISs will not use the overloaded IS to forward traffic. An IS can be inthe overload state for Level-1, Level-2, or both.• If an IS is in the overload state for Level-1, other Level-1 ISs stop using the overloaded IS toforward Level-1 traffic. However, the IS can still forward Level-2 traffic, if applicable.• If an IS is in the overload state for Level-2, other Level-2 ISs stop using the overloaded IS toforward Level-2 traffic. However, the IS can still forward Level-1 traffic, if applicable.• If an IS is in the overload state for both levels, the IS cannot forward traffic at either level.By default, the device automatically sets the overload bit to 1 (on) in its LSPDUs to other ISs if anoverload condition occurs.You can set the overload bit on to administratively shut down IS-IS without disabling the protocol.Setting the overload bit on is useful when you want to make configuration changes withoutremoving the device from the network.In addition, you can configure the device to set the overload bit on for a specific number of secondsduring startup, to allow IS-IS to become fully active before the device begins IS-IS routing. Bydefault, there is no delay (0 seconds).To immediately set the overload bit on, enter the following command.BigIron RX(config-isis-router)# set-overload-bitThis command administratively shuts down IS-IS by configuring the device to immediately set theoverload bit to 1 (on) in all LSPs sent to other ISs.To configure the device to temporarily set the overload bit on after a software reload, enter acommand such as the following.BigIron RX(config-isis-router)# set-overload-bit on-startup 5This command configures the device to set the overload bit on in all its IS-IS LSPs sent to other ISsduring the first five seconds following a successful software reload. After the five seconds expire,the device resets the overload bit to off in all its IS-IS LSPs.Syntax: [no] set-overload-bit [on-startup ]
