Globally Configuring Is-Is On A Device; Setting The Overload Bit - Dell PowerConnect B-RX Configuration Manual

28

Globally configuring IS-IS on a device

•
•
Some IS-IS parameter changes take effect immediately while others do not take full effect until you
disable, then re-enable route redistribution.
Globally configuring IS-IS on a device
This section describes how to change the global IS-IS parameters. These parameter settings apply
to both IS-IS IPv4 and IS-IS IPv6, although IPv6 is currently not supported.

Setting the overload bit

If 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 ISs
from 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 in
the overload state for Level-1, Level-2, or both.
•
•
•
By default, the device automatically sets the overload bit to 1 (on) in its LSPDUs to other ISs if an
overload 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 without
removing the device from the network.
In addition, you can configure the device to set the overload bit on for a specific number of seconds
during startup, to allow IS-IS to become fully active before the device begins IS-IS routing. By
default, there is no delay (0 seconds).
To immediately set the overload bit on, enter the following command.
BigIron RX(config-isis-router)# set-overload-bit
This command administratively shuts down IS-IS by configuring the device to immediately set the
overload 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 a
command such as the following.
BigIron RX(config-isis-router)# set-overload-bit on-startup 5
This command configures the device to set the overload bit on in all its IS-IS LSPs sent to other ISs
during 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 <secs>]
874
Change the default metric.
Add, change, or negate route redistribution parameters.
If an IS is in the overload state for Level-1, other Level-1 ISs stop using the overloaded IS to
forward 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 to
forward 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.
BigIron RX Series Configuration Guide
53-1002253-01