Abnormal lag=Not being portforwarded or having an antivirus/firewall which blocks your Kai. I highly doubt you're concerned by the latter since you're on Linux. You aren't just portforwarded properly.
First, set a static Ip to your Internet's device: http://corz.org/comms/hardware/route...ip.address.php . See the Linux's part of this guide. If you're stuck at this part, I can't help you more since I don't know a shit about Linux OS. You'll have to find an alternative way to set your static IP then.
Secondly, open the UDP 30000 port to this static Ip by applying the appropriate guide according to your router: http://portforward.com/english/appli...k_Kaiindex.htm
And set 30000 port as the Kai's port in the Kai's configuration for the final touch.
If you still lag out then it's on your opponent's side and he'll have to portforward too.