It is possible to automatically bring up a network interface without any IP address configuration in Debian. This can be useful for e.g. traffic flow monitoring where the interface is subsequently placed in promiscuous mode by software such as tcpdump.

Like always, all network interface configuration is stored in the file /etc/network/interfaces. For the interface you want to bring up without an IP address, add these lines:

iface eth0 inet manualpre-up ifconfig $IFACE uppost-down ifconfig $IFACE down

If the interface is a VLAN interface, the up/down commands must be executed after/before the VLAN hooks, so it should then read:

iface eth0.2 inet manualpost-up ifconfig $IFACE uppre-down if  ...