Configuring IS-IS Advertising Default Routes

On edge devices with external routes, using the following commands configure to advertise a default route. This allows the device to advertise a default route (0.0.0.0/0) within the IS-IS routing domain.

set protocols isis area-tag <text> [vrf <vrf-name>] default-information originate <ipv4-routing | ipv6-routing> <level-1 | level-2> route-map <route-map>

set protocols isis area-tag <text> [vrf <vrf-name>] default-information originate <ipv4-routing | ipv6-routing> <level-1 | level-2> always

set protocols isis area-tag <text> [vrf <vrf-name>] default-information originate <ipv4-routing | ipv6-routing> <level-1 | level-2> metric <metric>

If there are multiple edge devices, you can configure a route policy with the parameter route-map <route-map> to specify the conditions under which a particular edge device should advertise the default route. This helps prevent routing black-holing. Additionally, you can use the parameter metric <metric> to set the cost value for the default route.

After applying this configuration, other devices within the IS-IS domain will forward traffic destined for external routing domains to this device first. Then, the traffic will be forwarded to the external routing domain through this device.