Routing and Protocols

Routing in Internet is carried out at the IP level and concentrates on determining
where IP datagrams are transmitted through the different physical
networks making up the Internet before arriving at their destination. To
study routing in the Internet, it is important to bear in mind that the architecture
is made up of heterogeneous physical networks interconnected by
gateways. A gateway is therefore a machine connected to more than one
physical network and with routing capability (i.e., able to pass IP datagrams
among the different networks to which it is connected).
Routing in the Internet is especially complex, due to the distinct characteristics
of the component networks. Ideally, the routing must take into
account aspects such as datagram length, network traffic, and the required
type of service; however, normally it is based on a fixed table containing the
shortest path to reach a specific destination.
Routing in the Internet is of two types: direct, where the datagram must
be sent to a machine in the same physical network, and indirect, where it is
necessary to access another physical network via a gateway.