IP routing and default gateway

IP routing and default gateway

Any NiagaraAX host on a network can communicate with another host on the same network. However, if a host wants to communicate outside its network, the administrator sets a default gateway on the host which is the IP address of a router used for communication with other networks.

The router examines an IP packet from the host and compares the destination address with a table of addresses it holds in memory. If it finds a match, it forwards the packet to the address associated with the table entry. This address could be on another network attached directly to the router, or the router may forward it to another router that knows about the network of the destination address.

Routers build these tables of destinations in a number of different ways. For simple networks, the router may load a table during start-up that was manually created by the administrator. However, more typically, routers use a broadcasting protocol to advertise the networks that they know about. Routers use other protocols to discover the shortest path between networks (the least number of hops from router to router). Routes are updated periodically to reflect changes in the availability of a route.