The abr-summary command configures route summarization on an area border router (ABR).
The undo abr-summary command disables route summarization on an ABR.
By default, route summarization is not configured on ABRs.
abr-summary ip-address mask [ cost { cost | inherit-minimum } | [ advertise [ generate-null0-route ] | not-advertise | generate-null0-route [ advertise ] ] ] *
undo abr-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. |
| advertise | not-advertise | Indicates whether to advertise the summarized route. By default, the summarized route is advertised. | - |
| cost cost | Specifies the cost of the summarized route. By default, the highest cost of specific routes is used as the cost of the summarized route. | The value is an integer that ranges from 0 to 16777214. |
| inherit-minimum | Indicates that the smallest cost of specific routes is used as the cost of the summarized route. | - |
| generate-null0-route | Generates a blackhole route to prevent routing loops. | - |
Usage Scenario
On a large-scale OSPF network, route search speed may decrease due to a large routing table size. Route summarization can be configured to reduce the size of the routing table 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 that IP address range. This prevents route flapping and improves network stability.
When the ABR sends routing information to other areas, it originates Type 3 LSAs for each network segment. If any contiguous segments exist in this area, run the abr-summary command to summarize these segments into one. The ABR then sends just one summarized LSA, and no LSAs that belong to the summarized network segment specified by the command. Therefore, the routing table size is reduced, and switch performance is improved.
Prerequisites
The network command has been run to specify the segments that need to be summarized before configuring route summarization.
Precautions
This command applies only to ABRs for intra-area route summarization. The asbr-summary command configures AS Boundary Routers (ASBRs) to summarize the routes imported by OSPF.
Route summarization cannot be configured on ABRs in different areas of the same process.
# In OSPF 100 area 1, summarize routes in two network segments, 10.42.10.0 and 10.42.110.0, into one route 10.42.0.0, and advertise the summarized route to other areas.
<HUAWEI> system-view [HUAWEI] ospf 100 [HUAWEI-ospf-100] area 1 [HUAWEI-ospf-100-area-0.0.0.1] network 10.42.10.0 0.0.0.255 [HUAWEI-ospf-100-area-0.0.0.1] network 10.42.110.0 0.0.0.255 [HUAWEI-ospf-100-area-0.0.0.1] abr-summary 10.42.0.0 255.255.0.0