The import-route isis level-2 into level-1 command controls route leaking from Level-2 areas to Level-1 areas. The command is configured on Level-1-2 routers connected to external areas.
The undo import-route isis level-2 into level-1 command disables the route leaking from Level-2 areas to Level-1 areas.
By default, Level-2 routing information is not leaked to a Level-1 area.
import-route isis level-2 into level-1 [ filter-policy { acl-number | ip-prefix ip-prefix-name | route-policy route-policy-name } | tag tag | direct { allow-filter-policy | allow-up-down-bit } ] *
undo import-route isis level-2 into level-1
undo import-route isis level-2 into level-1 [ filter-policy { acl-number | ip-prefix ip-prefix-name | route-policy route-policy-name } | tag tag | direct { allow-filter-policy | allow-up-down-bit } ] *
| Parameter | Description | Value |
|---|---|---|
| filter-policy | Filters the imported routes. | - |
| acl-number | Specifies the number of the basic ACL. | The value is an integer ranging from 2000 to 2999. |
| ip-prefix ip-prefix-name | Specifies the name of the IP address prefix. Only the routes that match the specified IP prefix are imported. | The name is a string of 1 to 169 case-sensitive characters, with spaces not supported. When double quotation marks are used around the string, spaces are allowed in the string. |
| route-policy route-policy-name | Specifies the name of the routing policy. | The name is a string of 1 to 40 case-sensitive characters, with spaces not supported. When double quotation marks are used around the string, spaces are allowed in the string. |
| tag tag | Specifies the administrative tag value assigned to the imported routes. | The value is an integer ranging from 1 to 4294967295. |
| direct allow-filter-policy | Indicates a filtering policy to filter the direct routes. If the parameter is configured, only the IS-IS Level-2 area direct routes that matches the filtering policy can leak to a Level-1 area. If the parameter is not configured, all Level-2 area direct routes will leak to a Level-1 area. |
- |
| direct allow-up-down-bit | Indicates that the Up or Down bit is used during direct route leaking. If direct allow-up-down-bit is specified, the direct routes that have already leaked to a Level-1 area cannot leak back. |
- |
Usage Scenario
IS-IS is designed for a hierarchical network. This means that routes of Level-1 areas are leaked to Level-2 areas, whereas routes of Level-2 areas are not leaked to Level-1 areas.
When multiple Level-1-2 routers in a Level-1 area are connected to a Level-2 area, Level-1 routers are unable to know the network topology of the Level-2 area, but forward traffic to the nearest Level-1-2 router (based on the route with the smallest cost). For Level-2 routers, however, this route may not be the optimal one. Therefore, you need to allow some Level-2 routes to be leaked to the Level-1 area to help Level-1 routers select the optimal route for forwarding traffic to the Level 2 area.
The import-route isis level-2 into level-1 command can be run only on Level-1-2 routers to allow all or some Level-2 routes to be leaked to the Level-1 area.
Prerequisites
IS-IS processes have been enabled.
Precautions
Creating an ACL before it is referenced is recommended. If a nonexistent ACL is referenced using the command, all routes in the Level-2 area leak to the Level-1 area.
Creating an IP prefix list or route-policy before it is referenced is recommended. By default, nonexistent IP prefix lists or route-policies cannot be referenced using the command. If the route-policy nonexistent-config-check disable command is run in the system view and a nonexistent IP prefix list or route-policy is referenced using the current command, all routes in the Level-1 area leak to the Level-2 area.