OSPF Area Design Advantages

erickafabiana

In the Cisco Press book 200-105 Wendell Odom speaks of advantages of OSPF Area Designs. In one of the bulletins he says

- Changes in the network (for example, links failing and recovering) require SPF calculations only on routers connected to the area where the link changed state, reducing the number of routers that must rerun SPF.

Im assuming that statement ^ refers to a redundant path within that Specific Area ^ still being able to reach a specific network because of convergence so the routers in that area are able recalculate SPF ?


Also the routers in different areas do not need to recalculate but still get notified that the link went down ?
They get notified via an LSA ?


I am new to the ICND2 and was debating going into a LAB to test this

ccie14023

Inter-area routing in OSPF is distance vector, so while routers external to the area do learn about the route being down, they do not need to run SPF. It is not necessary for a redundant link to be available. Say network X on router 1 goes down, and router 1 is the only link to network X for the area. We still need to run SPF to see if any paths exist to that link. If we have a redundant path then we will use it, but it's not needed.