asbr-summary

Function

The asbr-summary command configures an ASBR to summarize routes imported by OSPF.

The undo asbr-summary command disables an ASBR from summarizing routes imported by OSPF.

By default, an ASBR does 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 type

undo asbr-summary ip-address mask

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. The default value is 1.
cost cost	Indicates the cost of the summarized route.	The value is an integer ranging from 0 to 16777214. By default: For Type-1 external routes, the cost of the summarized route is the highest among the cost of the routes being summarized. For Type-2 external routes, the cost of the summarized route equals the highest among the cost of the routes being summarized plus 1.
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.	-

Views

OSPF view

Default Level

2: Configuration level

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 routers is improved.

After route summarization:

If a local router is an ASBR in an NSSA, the local router summarizes all imported Type-5 LSAs within the summary address range.
If the local router is an ASBR in an NSSA, the local router summarizes all imported Type-5 and Type-7 LSAs within the summary address range.
If the local router functions as both an ASBR and an ABR in an NSSA, the local router 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

When a large number of routes are summarized, 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.

Example

# Configure an ASBR to summarize all imported routes in the network segment 10.2.0.0, and set the tag of the summarized route to 2, and its cost to 100. Configure for the ASBR not to advertise the summarized route.

<sysname> system-view

[sysname] ospf 100

[sysname-ospf-100] asbr-summary 10.2.0.0 255.255.0.0 not-advertise tag 2 cost 100

# Enable OSPF to refer to Type-5 LSAs that are translated from Type-7 LSAs as well when it sets types and costs for summary routes on ASBRs.

<sysname> system-view

[sysname] ospf 100

[sysname-ospf-100] asbr-summary type nssa-trans-type-reference cost nssa-trans-cost-reference