Ospf features
# can simplify physical topology to less complex logical topology (adjacency reduction)
# can divide the whole network into several smaller network (the AREA concept)
# support different type of service (TOS)
- a link has multiple link cost
* link cost for TOS #1
* link cost for TOS #2
- this feature help supporting quality of service, but usually not used through
# unlike RIP/BGP, it does not use TCP/UDP
- OSPF sends its messages directly over IP