A null route is a route that goes to nowhere.
The reason for creating a null route is to prevent your system from sending any data to a remote system.
Creating a null route
Null routes are usually created using the `route` command. This works under both Windows and Unix, although the syntax differs.
The example shows the creation of a null route for an entire Class C network:
# route add 188.8.131.52 0.0.0.0
add net 184.108.40.206: gateway 0.0.0.0
We can see the route which this command created using the `netstat -nr` command:
# netstat -nr
Destination Gateway Flags Refs Use Netif Expire
193.252.19 0.0.0.0 UGS 0 0 fxp0
The result of this command is that no matter what packets we receive from this network, we will never send any packets to this network in reply.
Null routes are useful against spammers and other nasty folks on the Internet.