How is IP routing implemented?
Assuming that using various routing algorithms the best routing policy are obtained which gives the shortest distance between source and destination, the next question will be how to implement the actual routing. In IP, routing is done by routing table lookups. The key element in IP routing is the routing table maintained by the operating system. When a IP datagram is to be delivered by the IP layer, the routing decision along the path to the destination is made on a hop-by-hop bases. In other words, the IP layer does not know the complete route to any destination, unless it’s in the same subnet as the source. The following summerizes what the IP layer does for the routing: • Searching for a matching host address in the routing table. If a complete match is found, it sends the datagram to the destination. If the destination is really where the datagram is suppose to go, that’s the end of the story. But if the destination is actually a router, which means that the datagram is not direct
