How to configure an interface without any IP? How to remove IP address from an interface?
Well there may be many ways but I'll tell you only two of them, one that I used to follow and the other I am currently following.
Remember I'm talking about freebsd.
One way is to edit /etc/rc.conf file and remove the line
Then either run /etc/netstart or reboot the machine.
The other simple way is ifconfig your_interface_name -alias
Make sure that your interface is up. Just verify from ifconfig or run ifconfig your_interface_name up