Multiarea OSPF Overview
Multiarea OSPF is used in large or enterprise networks where there are so many routers that having every router communicating every link in their link state database with every other router in the network, even when it is a small change becomes taxing on the network. In this type of situation you don’t need every router, lets say there are 30 or more routers, running the shortest path first algorithm if an interface is momentarily shut down.
The solution is to use multi-area OSPF instead of single area OSPF where every network is in Area 0. In multiarea OSPF you still have to have a backbone area named Area 0 but you can add additional networks in other areas. The result is that routers will only share their entire link state databases with routers in there own area and other areas will be configured to receive only summary information from the area. This way, when there is a change in the network the SPF algorithm will only need to run on routers in the effected area.
I created a packet tracer lab activity that goes with a video tutorial series. Watch all of the videos in-order below, while you follow along with the downloadable packet activity here: multi-area-ospf-begin
Multiarea OSPF Video Tutorial