ASGAUR

If the alias is on the same subnet as an address already configured on the interface, then add netmask 0xffffffff to your ifconfig(8) command-line, as in the following:

    # ifconfig ed0 alias 192.0.2.2 netmask 0xffffffff

Otherwise, just specify the network address and netmask as usual:

    # ifconfig ed0 alias 172.16.141.5 netmask 0xffffff00