5.2 Configuring OSPF Operation Across Multiple Areas
5.2.3 Updating the routing table

After all routers receive the routing updates, they add them to their link-state databases and recalculate their routing tables. The order in which paths are calculated is as follows:

  1. All routers first calculate the paths to destinations within their area and add these entries into the routing table. These are the Type-1 and Type-2 LSAs.
  2. All routers then calculate the paths to the other areas within the internetwork. These paths are the inter-area route entries, or Type-3 and Type-4 LSAs. If a router has an inter-area route to a destination and an intra-area route to the same destination, the intra-area route is kept.
  3. All routers, except those that are in a form of stub area, then calculate the paths to the AS external (Type-5) destinations.

At this point, a router can reach any network within or outside the OSPF autonomous system.