Configuring OSPF route summarization
Configure route summarization on an ABR or ASBR to summarize contiguous networks into a single network and distribute it 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 more specific LSAs so that 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 ] | By default, no route summarization is configured. The command takes effect only on an ABR. |
Configuring route summarization when redistributing routes into OSPF on an ASBR
Without route summarization, an ASBR advertises each redistributed route in a separate ASE LSA. After you configure a summary route, the ASBR advertises only the summary route in an ASE LSA instead of more specific routes, reducing the number of LSAs in the LSDB.
The ASBR summarizes redistributed Type-5 LSAs within the specified address range. If the ASBR is in an NSSA area, it also summarizes Type-7 LSAs within the specified address range. If the ASBR is also the ABR, it summarizes Type-5 LSAs translated from Type-7 LSAs.
To configure route summarization when redistributing routes into OSPF 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 | not-advertise | nssa-only | tag tag ] * | By default, no ASBR route summarization is configured. The command takes effect only on an ASBR. |