Configuring OSPF route summarization
Route summarization enables an ABR or ASBR to summarize contiguous networks into a single network and advertise the network to other areas.
Route summarization reduces the routing information exchanged between areas and the size of routing tables, and improves routing performance. For example, three internal networks 19.1.1.0/24, 19.1.2.0/24, and 19.1.3.0/24 are available within an area. You can summarize the three networks into network 19.1.0.0/16, and advertise the summary network to other areas.
Configuring route summarization on an ABR
After you configure a summary route on an ABR, the ABR generates a summary LSA instead of specific LSAs. The scale of LSDBs on routers in other areas and the influence of topology changes are reduced.
To configure route summarization on an ABR:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter OSPF view. | ospf [ process-id | router-id router-id | vpn-instance vpn-instance-name ] * | N/A |
3. Enter OSPF area view. | area area-id | N/A |
4. Configure ABR route summarization. | abr-summary ip-address { mask-length | mask } [ advertise | not-advertise ] [ cost cost-value ] | By default, route summarization is not configured on an ABR. |
Configuring route summarization on an ASBR
Perform this task to enable an ASBR to summarize external routes within the specified address range into a single route. The ASBR advertises only the summary route to reduce the number of LSAs in the LSDB.
An ASBR can summarize routes in the following LSAs:
Type-5 LSAs.
Type-7 LSAs in an NSSA area.
Type-5 LSAs translated by the ASBR (also an ABR) from Type-7 LSAs in an NSSA area.
If the ASBR (ABR) is not a translator, it cannot summarize routes in Type-5 LSAs translated from Type-7 LSAs.
To configure route summarization on an ASBR:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter OSPF view. | ospf [ process-id | router-id router-id | vpn-instance vpn-instance-name ] * | N/A |
3. Configure ASBR route summarization. | asbr-summary ip-address { mask-length | mask } [ cost cost-value | not-advertise | nssa-only | tag tag ] * | By default, route summarization is not configured on an ASBR. |