Internetworking is the practice of connecting a computer network with other networks through the use of gateways that provide a common method of routing information packets between the networks. The resulting system of interconnected networks are called an internetwork, or simply an internet. Internetworking is a combination of the words inter ("between") and networking; not internet-working or international-network.In real world scenario, networks under same administration are generally scattered geographically. There may exist requirement of connecting two different networks of same kind as well as of different kinds. Routing between two networks is called internetworking.
Today the interconnecting gateways are called routers.
Internetworking is implemented in the Network Layer (Layer 3) of the model.
Networks can be considered different based on various parameters such as, Protocol, topology, Layer-2 network and addressing scheme.
In internetworking, routers have knowledge of each other’s address and addresses beyond them. They can be statically configured go on different network or they can learn by using internetworking routing protocol.
Internetwork address : The combination of the network address and the host address; it uniquely identifies a host on an internetwork. An IP address that contains a network ID and a host ID is an internetwork address.
For more info visit here:http://www.doc.ic.ac.uk/~pjm/nac/lecture_routing.pdf
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