I need to configure my machine as to allow HTTP traffic to/from serverfault.com only. All other websites, services ports are not accessible. I came up with these iptables rules: #drop everything iptables -P INPUT DROP iptables -P OUTPUT DROP #Now, allow connection to website serverfault.com on port 80 iptables -A OUTPUT -p tcp -d serverfault.com --dport 80 -j ACCEPT iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT #allow loopback iptables -I INPUT 1 -i lo -j ACCEPT It doesn't work quite well: After I drop everything, and move on to rule 3: iptables -A OUTPUT -p tcp -d serverfault.com --dport 80 -j ACCEPT I get this error: iptables v1.4.4: host/network `serverfault.com' not found Try `iptables -h' or 'iptables --help' for more information. Do you think it is related to DNS? Should I allow it as well? Or should I just put IP addresses in the rules? Do you think what I'm trying to do could be achieved with simpler rules? How? I would appreciate any help or hints on this. Thanks a lot!