Open Shortest Path First(OSPF)

OSPF (Open Shortest Path First) protocol is the Internet Network Engineering (IETF) developed an internal gateway protocol (IGP), the gateway and router are within an autonomous system. OSPF is a link state protocol, or shortest path first (SPF) protocol. Although the protocol relies on IP environment than some of the technology, but the agreement specific to IP, but also the function of subnet addressing. The agreement in accordance with the purpose of IP datagram for routing IP address, once you've decided how to choose the path of a IP datagram, the datagram will be sent to the chosen path, no additional header, that is, there is no additional package. This method is different with many networks because they use some type of internal network of the UDP encapsulation header to control the subnet routing protocol. In addition OSPF in a very short period of time to make routing table convergence. OSPF also be able to prevent loops, this ability for the mesh network or use multiple bridges connecting the different LANs is very important. Each running OSPF router maintains an autonomous system topology described in a unified database that each router by the local state information (the router interface information available, neighbor information), the router connected to the network status information ( The network is connected to the router), the external state information (outside the autonomous system routing information) and so on. Each router within the autonomous system in the spread of the corresponding status information.
All routers run the same algorithm in parallel, according to the router's topology database constructed for the root node in its own shortest path tree, the shortest path tree is a leaf node to other routers within the autonomous system. When you get there the same purpose routers cost more than the same route, OSPF can be achieved in the distribution of traffic on multiple paths.
RFC2178 OSPF's TOS deleted features, but in order to ensure compatibility with previous versions, in all the link state declaration also retained the TOS project.