Allow web and ssh connections SSH and web both require out going messages on established tcp connections.
iptables -A OUTPUT -o eth0 -m state –state ESTABLISHED,RELATED -j ACCEPT
Then you need to allow incomming connections on port 80 and 22 and possibly 443
iptables -A INPUT -p tcp -i eth0 –dport 22 –sport 1024:65535 -m state –state NEW -j ACCEPT
iptables -A INPUT -p tcp -i eth0 –dport 80 –sport 1024:65535 -m state –state NEW -j ACCEPT
iptables -A INPUT -p tcp -i eth0 –dport 443 –sport 1024:65535 -m state –state NEW -j ACCEPT
To allow a DNS server to operate use the following rules (assuming your blocking inbound and outbound in iptables)
DNS communicated in to destination port 53 but can come from any port in the upper range. So these rules require a large section of ports to allow access as long as they want to talk to 53.
iptables -A OUTPUT -p udp –dport 53 –sport 1024:65535 -j ACCEPT
iptables -A INPUT -p udp –dport 53 –sport 1024:65535 -j ACCEPT
