Default route

A default route is the network route used by a Router when no other known route works for a given Internet Protocol packet s destination address. A router determines which route is valid to reach an IP address by finding the Longest prefix match . That is, the network with the longest subnet mask that matches the IP address, wins.

The default route in IPv4 (in Classless Inter-Domain Routing notation) is 0.0.0.0/0. Since the subnet mask given is /0, it effectively specifies no network, and is the shortest match possible. A route lookup that doesn t match anything, will naturally fall back onto this route.

Hosts and routers in an organization generally point the default route towards the router that has a connection to a network service provider. This way, packets destined towards the internet will be sent towards the router with the internet connection.