Nullroute
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In computer networking, a nullroute is a network route that goes nowhere.
When a network packet is received by the operating system, it needs to route that packet somewhere. It uses the routing table to decide where to send the packet. To "kill" the packet, in essence dropping the packet and forbidding the packet from travelling further, a nullroute (or null route) could be put in place.
With a route that goes nowhere, the system then will not be able to forward the packet, and the transmission dies at this host.
Nullroute can also refer to a DNS entry pointing nowhere.
[edit] Technical details
Nullrouting can be performed by adding a route to an invalid or nonexisting host, or to the loopback address.
A similar (and much cleaner) effect can be done by dropping all packets at the firewall.
[edit] Specific examples
Nullrouting with 'route' on Linux:
$ route add -host 192.168.32.128 reject
Nullrouting with 'iproute' on Linux:
$ ip route add blackhole 192.168.32.128/32
