The asbr-summary command configures an AS Boundary Router (ASBR) to summarize the routes imported by OSPF.
The undo asbr-summary command disables an ASBR from summarizing the routes imported by OSPF.
By default, ASBRs do not summarize the routes imported by OSPF.
asbr-summary ip-address mask [ [ not-advertise | generate-null0-route ] | tag tag | cost cost | distribute-delay interval ] *
asbr-summary type nssa-trans-type-reference [ cost nssa-trans-cost-reference ]
undo asbr-summary type
undo asbr-summary ip-address mask
| Parameter | Description | Value |
|---|---|---|
ip-address |
Specifies the IP address of a summarized route. |
The value is in dotted decimal notation. |
mask |
Specifies the mask of the IP address of the summarized route. |
The value is in dotted decimal notation. |
not-advertise |
Indicates that the summarized route is not advertised. If this parameter is not specified, the summarized route is advertised. |
- |
generate-null0-route |
Generates a blackhole route to prevent routing loops. |
- |
tag tag |
Specifies the tag of the summarized route. |
The value is an integer that ranges from 0 to 4294967295. The default value is 1. |
cost cost |
Specifies the cost of the summarized route. By default, for Type 1 external routes, the cost of the summarized route is the highest cost of specific routes; for Type 2 external routes, the cost of the summarized route equals the highest cost of specific routes plus 1. |
The value is an integer that ranges from 0 to 16777214. |
distribute-delay interval |
Specifies the delay in advertising the summarized route. |
The value is an integer that ranges from 1 to 65535, in seconds. |
type nssa-trans-type-reference |
Enables OSPF to consider Type 5 LSAs that have been translated from Type 7 LSAs when it sets types for summary routes on ASBRs. By default, when OSPF sets types for summary routes on ASBRs, OSPF does not consider Type 5 LSAs that have been translated from Type 7 LSAs. |
- |
cost nssa-trans-cost-reference |
Enables OSPF to consider Type 5 LSAs that have been translated from Type 7 LSAs when it sets costs for summary routes on ASBRs. If the asbr-summary type nssa-trans-type-reference cost nssa-trans-cost-reference command is not run, OSPF does not consider Type 5 LSAs that have been translated from Type 7 LSAs when setting types and costs for summary routes on ASBRs. |
- |
Usage Scenario
On a large-scale OSPF network, route search speed may decrease due to a large routing table size. Configure route summarization to reduce the routing table size and simplify management.
Route summarization aggregates multiple routes with the same IP prefix into one. If a link connected to a device within a summarized IP address range alternates between Up and Down states, the link status change is not advertised to the devices outside the IP address range. This prevents route flapping and improves network stability.
Imported routes with the same prefix can be summarized into one and advertised as one route using the asbr-summary command. Route summarization reduces routing information and routing table size, improving device performance.
After route summarization is implemented, if the local device:
Precautions
When a large number of routes are summarized, specify the distribute-delay parameter to set a delay in advertising the summarized routes. This ensures that the advertised summarized routes contain more valid routes and avoids network flapping and incorrect routing information.