Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) - Manual (Page 284)

256 Multi-Service IronWare Routing Configuration Guide
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Globally configuring IS-IS on a device
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 as described in the following section:
• 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.
By default, the Brocade 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 Brocade device from the network.
In addition, you can configure the Brocade 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.
Brocade(config-isis-router)# set-overload-bit
This command administratively shuts down IS-IS by configuring the Brocade device to immediately
set the overload bit to 1 (on) in all LSPs sent to other ISs.
To configure the Brocade device to temporarily set the overload bit on after a software reload, enter
a command such as the following.
Brocade(config-isis-router)# set-overload-bit on-startup 5
This command configures the Brocade 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 Brocade device resets the overload bit to off in all its IS-IS LSPs.
Syntax: [no] set-overload-bit [on-startup secs]
The on-startup secs parameter specifies the number of seconds following a reload to set the
overload bit on. You can specify a number from 5 – 86400 (24 hours).
A new option has been added to the set-overload-bit command to prevent route black holing in
support of RFC 3277. With this option set, the behavior of IS-IS will be changed during a device
reboot. During a device reboot, IS-IS sets the overload bit in its LSPDUs until BGP has converged.
This feature is configured using the set-overload-bit command as shown in the following.
Brocade(config-isis-router)# set-overload-bit on-startup wait-for-bgp 1000
Syntax: [no] set-overload-bit on-startup wait-for-bgp max-bgp-wait-time
The max-bgp-wait-time variable is the maximum time IS-IS will wait for BGP convergence to
complete. Once this time has been exceeded without BGP converging, IS-IS will exit the overload
state. The default value is 600 seconds (10 minutes), possible values range: 5 to 86400 seconds.