libpcap on vserver

Hello,

I would like to use knockd on my ubuntu edgy vserver. Ifconfig shows 3 devices:
lo, venet0 and venet0:0. On the venet0:0 alias I can see my external IP
adress, lo and venet0 have both 127.0.0.1/32. If I run knockd I get
this message: Starting Port-knock daemon: could not open venet0:0 /
venet0: arptype 65535 not supported by libpcap - falling back to cooked
socket

I don't know how to use knockd on my server. Can anyone help me please?

Thanks