Configuring IPv4 IS-IS to Import External Routes
If devices in an IS-IS routing domain need to learn external routes, configure IS-IS on a Level-1-2 device of this routing domain to import external routes.
Context
If IS-IS is configured on a Level-1-2 device to advertise a default route, all traffic in IS-IS routing domains will be forwarded by this Level-1-2 device. This will burden this Level-1-2 device because no external route can be learned on the devices in the IS-IS routing domains.
If multiple Level-1-2 devices are deployed, 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 domains must learn all or some external routes.
Routing policies can be configured to import or advertise external routes that meet specified conditions to the IS-IS routing domains.
Procedure
- Access the system view.
- Access the IS-IS process view.
isis [ process-id ]
- Configuring IS-IS to import external routes.
- If you want to set the cost for the imported route, run the import-route { direct | static | unr | { ospf | rip | isis } [ process-id ] | 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 import the external routes.
- If you want to keep the original cost for the imported route, run the import-route { { rip | isis | ospf } [ process-id ] | bgp [ permit-ibgp ] | direct } inherit-cost [ tag tag | route-policy route-policy-name | [ level-1 | level-2 | level-1-2 ] ] * command to import the external routes.
IS-IS will advertise all imported external routes to an IS-IS routing domain by default.
If only some imported external routes need to be advertised, run the filter-policy export command to set a filtering policy.
If an IS-IS device has a small routing table capacity, run the import-route limit limit-number [ threshold-alarm upper-limit upper-limit-value lower-limit lower-limit-value ] { level-1 | level-2 | level-1-2 } command to set the maximum number of external routes that can be imported into an IS-IS routing domain.
- Filter imported routes during the advertising to others.
filter-policy { acl-number | ip-prefix ip-prefix -name | route-policy route-policy-name } export [ protocol [ process-id ] ]
If the importing level is not specified in the import-route command, routes are imported into the Level-2 routing table by default.
To import direct routes and other routing policies on the same level at the same time, you should comply with the principle that the preference of the direct route is the highest.