Look for iptables -t mangle -A PREROUING chain
What i tried to do was a Prerouting
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 5050 -j REDIRECT --to-port 3128
and in my squid conf
acl chat_ports port 5050 http_access deny CONNECT !chat_ports
but i am still able to log in to the chat client
which port can i block for yahoo chat ??