Configuring IS-IS to Advertise a Default Route

Context

If IS-IS is configured to advertise a default route on a border device that has external routes, the device advertises a default route 0.0.0.0/0 in the IS-IS routing domain. All traffic destined for other routing domains is first forwarded to the border device.

Configuring a static default route can also allow all the traffic to be first forwarded to a border device, which then forwards the traffic outside an IS-IS routing domain. However, this method leads to heavy workload in configuration and management when a large number of devices are deployed on the network.

In addition, advertising default routes using IS-IS is flexible. If multiple border devices are deployed, a routing policy can be configured to allow only the border device that meets the specified conditions to advertise a default route, preventing routing blackholes.

Procedure

Run system-view
The system view is displayed.
Run isis [ process-id ]
The IS-IS view is displayed.
Run default-route-advertise [ always | match default | route-policy route-policy-name ] [ cost cost | tag tag | [ level-1 | level-1-2 | level-2 ] ] ^* [ avoid-learning ]
IS-IS is configured to advertise a default route.

By default, IS-IS does not advertise a default route.