Configuring IS-IS to Import External Routes
Context
After IS-IS is configured to advertise a default route on a border device in an IS-IS routing domain, all the traffic destined outside the IS-IS routing domain is forwarded through the border device. This burdens the border device because other devices in the IS-IS routing domain do not have the routes destined outside the domain. If multiple border devices are deployed in the IS-IS routing domain, optimal routes to other routing domains need to be selected.
To ensure optimal routes are selected, all the other devices in the IS-IS routing domain must learn all or some external routes.
Procedure
- Run system-view
The system view is displayed.
- Run isis [ process-id ]
The IS-IS view is displayed.
- Configure IS-IS to import external routes.
- When you need to set the cost of imported routes, run the import-route { { rip | isis | ospf } [ process-id ] | static | direct | unr | bgp [ permit-ibgp ] } [ cost-type { external | internal } | cost cost | tag tag | route-policy route-policy-name | [ level-1 | level-2 | level-1-2 ] ] * command to configure IS-IS to import external routes.
- When you need to retain the original cost of imported routes, run the import-route { { rip | isis | ospf } [ process-id ] | direct | unr | bgp } inherit-cost [ tag tag | route-policy route-policy-name | [ level-1 | level-2 | level-1-2 ] ] * command to configure IS-IS to import external routes. In this case, the source routing protocol of imported routes cannot be static.
IS-IS will advertise all imported external routes to the IS-IS routing domain by default.