I think that you can configure your firewall to limit the number of connections from the same IP address but I don't know how to do it in practice with iptables.
Anyway versus what service you have noticed the attack?
I think the following links will help you:
http://en.linuxreviews.org/Iptables_tips_and_tricks
http://icecast.imux.net/viewtopic.php?t=2512