Packet filter on a proxy for the game, how to do it?

Question

proxy

Game server (old game Tales of pirates 2008) on OVX hosting - Windows system
Proxied through a proxy on OVX - Linux system
The essence of the problem:
Competitors attack our server applications with packages with a valid header, stuff a large number of random characters into this package, the package is perceived as valid.
It turns out that when such a packet arrives at our application, it gets out of sync or crashes

. What and how to make a filter on a proxy server, some kind of program that can check the contents of packets, compare bytes within packets, create several stages of packet filtering? Help with advice

Answer 1

Can be done through iptables: an article with examples .
Detailed iptables dock in Russian: here .