CCNP Routing and Switching ROUTE 300-101 Official Cert Guide

Flooding Throughout the Area

So far in this section, the database exchange process has focused on exchanging the database between neighbors. However, LSAs need to be flooded throughout an area. To do so, when a router learns new LSAs from one neighbor, that router then knows that its other neighbors in that same area might not know of that LSA. Similarly, when an LSA changes—for example, when an interface changes state—a router might learn the same old LSA but with a new sequence number, and again need to flood the changed LSA to other neighbors in that area.

Figure 8-10 shows a basic example of the process. In this case, R2, R3, and R4 have established neighbor relationships, with four LSAs in their LSDB in this area. R1 is again the new router ...