Using the Null Interface

You can use access control lists to filter undesired traffic. Another way to handle undesired traffic is to send it to the null interface. The null interface is automatically created by the router, is always up, cannot be deleted, and acts as a data sink. In other words, the null interface cannot forward or receive traffic. However, the CLI does allow you to access the null interface.

The E-series router creates the null interface by default; you do not have to create it manually. You can direct traffic to the null interface by specifying the null 0 keywords instead of a next-hop or destination address when configuring routes.

interface null

• Use to access the null interface.
• The null interface is a data sink; it does not accept or forward traffic.
• Though you can access the null interface, you cannot configure any values for it or delete it.
• Example

host1(config)#interface null 0

host1(config-if)# 

• There is no no version.

ip route

• Use to configure a static route and redirect traffic from it to the null interface.
• Example

host1(config-if)#ip route 10.10.20.5 null 0

• Use the no version to remove the static route.