asbr-summary
Function
The asbr-summary command configures AS Boundary Routers (ASBRs) to summarize routes imported by OSPF.
The undo asbr-summary command disables ASBRs from summarizing routes imported by OSPF.
By default, ASBRs do not summarize routes imported by OSPF.
Format
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 ip-address mask
undo asbr-summary type
Parameters
| Parameter | Description | Value |
|---|---|---|
| ip-address | Specifies the IP address of a summarized route. | This value is in dotted decimal notation. |
| mask | Specifies the mask of the IP address of the summarized route. | This 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 | Specifies to generate a black-hole route in the RM module, which is used to prevent routing loops. |
- |
| tag tag | Specifies the tag of the summarized route. | The value is an integer ranging from 0 to 4294967295. By default, it 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 the routes being summarized; for Type 2 external routes, the cost of the summarized route equals the highest cost of the routes being summarized plus 1. | The value is an integer ranging from 0 to 16777214. |
| distribute-delay interval | Specifies the delay for advertising the summarized route. | The value is an integer ranging from 1 to 65535, in seconds. |
| type nssa-trans-type-reference | Enable OSPF to refer to Type 5 LSAs that are translated from Type 7 LSAs when it sets types for summary routes on ASBRs. If the asbr-summary type nssa-trans-type-reference command is not run, when OSPF set types for summary routes on ASBRs, OSPF does not refer to Type 5 LSAs that are translated from Type 7 LSAs. |
- |
| cost nssa-trans-cost-reference | Enable OSPF to refer to Type 5 LSAs that are 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 is not run, when OSPF set types and costs for summary routes on ASBRs, OSPF does not refer to Type 5 LSAs that are translated from Type 7 LSAs. |
- |
Usage Guidelines
Usage Scenario
On a large-scale OSPF network, route searching speed may decrease because of the large size of the routing table. You can configure route summarization to reduce the size of the routing table and simplify management.
Route summarization occurs when routes with the same IP prefix are summarized into one route. If a link connected to a device within an IP address range that has been summarized alternates between Up and Down, the link status change is not advertised to the devices not within the IP address range. This prevents route flapping and improves network stability.
Imported routes with the same prefix can be summarized into one route and be advertised as one route using the asbr-summary command. Route summarization reduces routing information and the size of routing tables. Therefore, the performance of devices is improved.
After route summarization:
- If a local device is an ASBR in an NSSA, the local device summarizes all imported Type 5 LSAs within the summary address range.
- If the local device is an ASBR in an NSSA, the local device summarizes all imported Type 5 and Type 7 LSAs within the summary address range.
- If the local device functions as both an ASBR and an ABR in an NSSA, the local device summarizes all imported Type 5 and Type 7 LSAs within the address range. It also summarizes the Type 5 LSAs that are transformed from Type 7 LSAs.
Precautions
When a large number of routes are summarized, you can configure the distribute-delay parameter to set the delay for advertising the summarized routes. This ensures that the summarized routes advertised each time contain more valid routes and avoids network flapping and incorrect routing information.
