OSPF Terminology
OSPF Areas: is similar to EIGRP (Enhanced Interior Gateway Routing Protocol) AS’s (Autonomous Systems). Areas are used to establish a heirarchical network. OSPF uses 4 types of areas.
Internal router: a router with all its interfaces participating in one area.
ABR (Area Border Router): a router with multiple area assignments, where it has several interfaces and if any of those interfaces belong to different areas.