The summary command configures IS-IS to generate summarized routes.
The undo summary command disables IS-IS from generating summarized routes.
By default, IS-IS does not generate summarized routes.
summary ip-address mask [ avoid-feedback | generate_null0_route | tag tag | [ level-1 | level-1-2 | level-2 ] ] *
undo summary ip-address mask [ level-1 | level-1-2 | level-2 ]
| Parameter | Description | Value |
|---|---|---|
| ip-address | Specifies the IPv4 address of a summarized route. | The value is in dotted decimal notation. |
| mask | Specifies the mask of the IP address of a summarized route. | The value is in dotted decimal notation. |
| avoid-feedback | Prevents summarized routes from being learned through SPF calculation. | - |
| generate_null0_route | Generates null0 routes to prevent routing loops. | - |
| tag tag | Assigns administrative tags to advertised routes. | The value is an integer that ranges from 1 to 4294967295. |
| level-1 | Summarizes only the routes imported into Level-1 areas. If no level is specified, Level-2 is used by default. | - |
| level-1-2 | Summarizes the routes imported into Level-1 areas and the backbone network. If no level is specified, Level-2 is used by default. | - |
| level-2 | Summarizes only the routes imported into the backbone network. If no level is specified, Level-2 is used by default. | - |
Usage Scenario
Route summarization on a large-scale IS-IS network efficiently reduces routing entries. This minimizes system resource consumption and maintains system performance.
If a link frequently alternates between Up and Down, the links not involved in the route summarization will not be affected. Therefore, route summarization prevents route flapping on the network and improves network stability.
Precautions
Configuring route summarization does not affect the routing table of the local device because each specific route is still displayed in the routing table. Route summarization reduces the flooding of LSPs. Routing tables of other devices that receive the LSP from the local device contain only one summarized routes but not specific routes. Specific routes are still displayed in the routing table of the device directly connected to the summarized network segment.
Both IS-IS routes and routes imported from other protocols can be summarized. The lowest cost among that of the routes that are summarized is used as the cost of the summarized route.