A unique feature of OSPF is its ability to adapt to different data link layer technologies. OSPF behaves differently depending on the network type:
In a single-area OSPF design (Area 0), every router knows every LSA. If the network has 500 routers, each router runs SPF on a database of 500 routers. This is computationally insane. Tadimety argues that areas are not optional—they are mandatory for any network with >50 routers.
