Interfaces to point-to-point networks need not be assigned IP address. When interface addresses are assigned, they are modeled as sub links, with each router advertising a stub connection to the other router’s interface address.
LSA: Link-State Advertisement(链路状态通告)
SPF： short path first
The topology of an area is invisible from the outside of the area. Conversely, routers internal to a given area know nothing of the detailed topology external to the area. This isolation of knowledge enables the protocol to effect a marked reduction in routing traffic as compared to treating the entire Autonomous System as a single link-state domain.
Each area border router in an area summarizes for the area its cost to all networks external to the area. After the SPF tree is calculated for the area, routes to all inter-area destinations are calculated by examining the summaries of the are border routers.
IP TOS field set to 0.
The IP multicast datagrams used by OSPF never travel more than on hop.
Supernetting has been proposed as one way to improve the scaling of IP routing in the worldwide Internet.
OSPF simplifies this by requiring only adjacent routers to remain synchronized.
The Designated Router is elected by the Hello Protocol.