To enable communication in internetworking, every individual network node is designed with TCP or IP . internetworking is when a network communicates with other network having constant communication procedures. There are mainly three units of interworking : extranet, intranet and internet. Intranets and extranets might or might not have connections with the net. Routing is a process which is mainly performed in layer 3 of the OSI model. Layer 3 is network layer. Routing is also categorized as static routing, dynamic routing and default routing.