asbr-summary

Function

The asbr-summary command configures an AS boundary router (ASBR) 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-value | cost cost-value | distribute-delay interval ] ^*

undo asbr-summary ip-address mask

Parameters

Parameter	Description	Value
ip-address	Specifies the IP address of a summary route.	The value is in dotted decimal notation.
mask	Specifies the mask of the IP address of the summary route.	The value is in dotted decimal notation.
not-advertise	Prevents the summary route from being advertised. If this parameter is not specified, the summary route is advertised.	-
generate-null0-route	Generates a black-hole route in the RM module to prevent routing loops.	-
tag tag-value	Specifies the tag of the summary route.	The value is an integer ranging from 0 to 4294967295.
cost cost-value	Specifies the cost of the summary route.	The value is an integer ranging from 0 to 16777214. By default: For Type 1 external routes, the largest cost of the routes for summarization is used as the cost of the summary route. For Type 2 external routes, the largest cost of the routes for summarization plus 1 is used as the cost of the summary route.
distribute-delay interval	Specifies the delay for advertising the summary route.	The value is an integer ranging from 1 to 65535, in seconds.

Views

OSPF view

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
ospf	write

Usage Guidelines

Usage Scenario

On a large-scale OSPF network, route lookup may slow down because of the large size of the routing table. To reduce the size of the routing table and simplify management, configure route summarization.

Routes with the same IP prefix can be 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 beyond 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 advertised as one route using the asbr-summary command. Route summarization reduces the routing table size and improves device performance.

After route summarization:

If the local device is an ASBR in a common area, the local device summarizes all imported Type 5 LSAs within the summarized address range.
If the local device is an ASBR in an NSSA, the local device summarizes all imported Type 7 LSAs within the summarized address range.
If the local device functions as both an ASBR and 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 translated from Type 7 LSAs.

Precautions

In case of a large number of summary routes, you can set a delay in advertising them. This ensures that the summary routes advertised each time contain more valid routes and prevents incorrect routing information in case of network flapping.

Example

# Configure route summarization for imported routes.

<HUAWEI> system-view
[~HUAWEI] ospf 100
[*HUAWEI-ospf-100] asbr-summary 10.2.0.0 255.255.0.0 not-advertise tag 2 cost 100