hi in our company we have at list 20 computer connect to the internet,at first our access run smooth and fast enought to surf the web but suddenly it become so slow i discover that some of my user are using imesh and yahoo messenger and even getright to download mp3 and mpeg movie... the question is how do i block does program??? pls help me my boss is getting angry of slow connections thks in advance

downloading is probably the main culprit

you can block any undesired web traffic you want with a proxy server.

I used dansguardian a long time ago. There's also squidguard and many others.

What you want to do is setup the iptables rules to redirect all web traffic through the proxy server

# Transparent proxy
$IPTABLES -A PREROUTING -t nat -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 3128
$IPTABLES -A PREROUTING -t nat -i eth2 -p tcp --dport 80 -j REDIRECT --to-port 3128
$IPTABLES -A PREROUTING -t nat -i ppp0 -p tcp --dport 80 -j REDIRECT --to-port 3128

monitor traffic with iptraf you can see what other ports are getting a lot of traffic, you can shut them down with iptables rules


$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 32768 -j DROP

what is --dport 32768??? is this the port that imesh or yahoo messenger are using??? an followup iam just using 2 lan card in my gateway server eth0 for my public 203.23.x.x and eth1 for my internal network private 192.168.0.1 iam connected via wireless internet.... which will i use the 1st ,2nd or both??

that port is just an example

just open the port you want them to use like port 80 and close all others

create new tables..
$IPTABLES -N udp_in
$IPTABLES -N tcp_in

redirect the tcp and udp traffic on the interface to the new tables..
$IPTABLES -A INPUT -p TCP -i eth1 -j tcp_in
$IPTABLES -A INPUT -p UDP -i eth1 -j udp_in

example open tcp ports..
$IPTABLES -A tcp_in -p TCP -s 0/0 --dport 25 -j ACCEPT
$IPTABLES -A tcp_in -p TCP -s 0/0 --dport 80 -j ACCEPT

close all others..
$IPTABLES -A tcp_in -p TCP -j DROP

example open udp port..
$IPTABLES -A udp_in -p UDP -s 0/0 --source-port 53 -j ACCEPT

close all others..
$IPTABLES -A udp_in -p UDP -j DROP


then get ready for some angry people

it's probably better to leave it open then close offending ports as needed like I have shown above

Try this

iptables -A FORWARD --p TCP --dport 5000:5100 -j REJECT
iptables -A FORWARD -d cs.yahoo.com -j REJECT
iptables -A FORWARD -d scsa.yahoo.com -j REJECT
iptables -A FORWARD -d scsa.msg.yahoo.com -j REJECT

OR/ AND if still not blocked

FW_MASQ_NETS="192.168.1.0/24,0/0,TCP,5000:5100"