IP forwarding algorithm

The IP Forwarding Algorithm is related to the topic of routing and gives a more directed approach in forwarding datagrams over a network. In order to achieve a successful transfer of data the algorithm uses a routing table to select a next-hop router as the next destination for a datagram given that a direct connection has not been advertised. The IP address that is selected as is known as the next-hop address.

The IP Forwarding Algorithm states:

Given a destination IP address, D, and network prefix, N:

if (N matches a directly connected network address)

 Deliver datagram to D over that network;

else if (N does not match a network address and routing table contains route for N)

 Send datagram to next-hop address listed in the routing table;

else if (N does not match a network and routing table does not contain route for N and there exists a default route)

 Send datagram to default route;

else

 Send forwarding error message;