Internetworking with TCP/IP- P36: TCP/IP has accommodated change well. The basic technology has survived nearly two decades of exponential growth and the associated increases in traffic. The protocols have worked over new high-speed network technologies, and the design has handled applications that could not be imagined in the original design. Of course, the entire protocol suite has not remained static. New protocols have been deployed, and new techniques have been developed to adapt existing protocols to new network technologies | Sec. The Open SPF Protocol OSPF 309 OSPF includes type of service routing. Managers can install multiple routes to a given destination one for each priority or type of service. When routing a datagram a router running OSPF uses both the destination address and type of service field in an IP header to choose a route. OSPF is among the first TCP IP protocols to offer type of service routing. OSPF provides load balancing. If a manager specifies multiple routes to a given destination at the same cost OSPF distributes traffic over all routes equally. Again OSPF is among the first open IGPs to offer load balancing protocols like RIP compute a single route to each destination. To permit growth and make the networks at a site easier to manage OSPF allows a site to partition its networks and routers into subsets called areas. Each area is selfcontained knowledge of an area s topology remains hidden from other areas. Thus multiple groups within a given site can cooperate in the use of OSPF for routing even though each group retains the ability to change its internal network topology independently. The OSPF protocol specifies that all exchanges between routers can be authenticated. OSPF allows a variety of authentication schemes and even allows one area to choose a different scheme than another area. The idea behind authentication is to guarantee that only trusted routers propagate routing information. To understand why this could be a problem consider what can happen when using RIP1 which has no authentication. If a malicious person uses a personal computer to propagate RIP messages advertising low-cost routes other routers and hosts running RIP will change their routes and start sending datagrams to the personal computer. OSPF includes support for host-specific subnet-specific and classless routes as well as classful network-specific routes. All types may be needed in a large internet. To accommodate multi-access networks like Ethernet OSPF extends the SPF algorithm .
