The principle criterion of successful routing is of course correctness but it not only criterion. You might prefer to take the most direct route ( the one that the least time and uses the least fuel) the most reliable route (the one is not likely to be closed by a heavy snowfall) the most scenic route ( the one that flows pleasant country roads rather than busy highways) the least expensive route ( the one that follow freeways rather than toll roads0 or the safest route ( the one that avoids the army missile testing range) in its most general form optimal routing involves forwarding a packet from source to destination using the best path.
Routing is the methods of delivering a message from source to target ( which are not directly connected )suing multiple other hosts in the middle to forward the message.
Routers perform two things to deliver the packets to its destination.
a.First is learning the logical of the network to store the path inside the routing table to where the traffic should flow which called routing.
b.Second is forwarding those packets learned from an inbound interface to the out bound interface with in the ourter which is called switching.
The observation suggest that an open systems routing architecture should.
a.Scale well .
b.Support many different sub network types and multiple qualities of service.
c.Adapt to topology changes quickly and efficiently ( i ,e with minimum overhead and complexity).
d.Provide controls that facilitate the safe connection of multiple organizations.
It is not likely that the manual administration of static routing tables will satisfy these objectives for a network connecting more than a few hundred systems. A routing scheme for a large scale open systems network must biodynamic adaptive and decentralized, be capable of supporting multiple paths offering different types of service and provide the means to establish trust firewalls and security across multiple administrations.