Configuring OSPF to Make Routing Devices Appear Overloaded

If the time elapsed after the OSPF instance is enabled is less than the specified timeout, overload mode is set.

You can configure the local routing device so that it appears to be overloaded. You might do this when you want the routing device to participate in OSPF routing, but do not want it to be used for transit traffic. (Traffic to directly attached interfaces continues to transit the routing device.)

You configure or disable overload mode in OSPF with or without a timeout. Without a timeout, overload mode is set until it is explicitly deleted from the configuration. With a timeout, overload mode is set if the time elapsed since the OSPF instance started is less than the specified timeout.

A timer is started for the difference between the timeout and the time elapsed since the instance started. When the timer expires, overload mode is cleared. In overload mode, the router LSA is originated with all the transit router links (except stub) set to a metric of 0xFFFF. The stub router links are advertised with the actual cost of the interfaces corresponding to the stub. This causes the transit traffic to avoid the overloaded routing device and take paths around the routing device. However, the overloaded routing device’s own links are still accessible.

To mark the routing device as overloaded, include the overload statement:

To specify the number of seconds at which overload is reset, include the timeout option when specifying the overload statement:

The time can be a value from 60 through 1800 seconds.

For a list of hierarchy levels at which you can include these statements, see the statement summary sections for these statements.