OSPF areas

[carl_townshend]

Can anyone tell me why we have areas in ospf, and what routes do ABR,s exchange, its it about all routes in that area ?

[bhedlund]

Dividing a large OSPF network into areas helps reduce the flooding of Type 1 LSA's throughout the network everytime the state of an interface changes. This helps the network scale and grow while maintaing routing protocol stability.

ABR's exchange Type 3/4 summary LSA's between areas, providing a barrier for the chatty Type 1 LSAs.

Please rate all helpful posts.

Regards,

Brad

[kthned]

Hi carl_townshend

Actually we use OSPF in a very large network (many routers) . OSPF is just used to divide the whole network to number of areas (we configure some routers in one area and some on different and so on). So if their is some network failure, the whole topology does not change but only the area in which that network fails suffer.

The Area Hierarchy is as follows for your info. there is one backbone (i.e. Area 0) and all the rest areas are connected to the backbone area.

The Router that connect the backbone and other area is ABR. and ABR exchange network of one area to another, but if you can configure to route summarized network (Interarea summarization) on ABR. to reduce routing table size.