I have Ubuntu 12.04 x64 installed in my laptop. I'm quite new to linux, and I wanted to specify certain rules for the iptables firewall. This is the saved config of my iptables: *mangle :PREROUTING ACCEPT [0:0] :INPUT ACCEPT [0:0] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [0:0] :POSTROUTING ACCEPT [0:0] COMMIT *nat :PREROUTING ACCEPT [0:0] :INPUT ACCEPT [0:0] :OUTPUT ACCEPT [0:0] :POSTROUTING ACCEPT [0:0] -A PREROUTING -p tcp -m tcp --dport 3306 -j DNAT --to-destination 192.168.1.100:3306 -A PREROUTING -p tcp -m tcp --dport 11002 -j DNAT --to-destination 192.168.1.100:11002 -A PREROUTING -p tcp -m tcp --dport 13000 -j DNAT --to-destination 192.168.1.100:13000 -A PREROUTING -p tcp -m tcp --dport 13001 -j DNAT --to-destination 192.168.1.100:13001 -A PREROUTING -p tcp -m tcp --dport 13002 -j DNAT --to-destination 192.168.1.100:13002 -A PREROUTING -p tcp -m tcp --dport 13003 -j DNAT --to-destination 192.168.1.100:13003 -A PREROUTING -p tcp -m tcp --dport 13004 -j DNAT --to-destination 192.168.1.100:13004 -A PREROUTING -p tcp -m tcp --dport 13061 -j DNAT --to-destination 192.168.1.100:13061 -A PREROUTING -p tcp -m tcp --dport 13099 -j DNAT --to-destination 192.168.1.100:13099 -A POSTROUTING -j MASQUERADE COMMIT *filter :INPUT DROP [0:0] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [0:0] -A INPUT -i eth0 -p tcp -m tcp --dport 3306 -j ACCEPT -A INPUT -i eth0 -p tcp -m tcp --dport 80 -j ACCEPT COMMIT In theory, what it does is to drop all connections in all ports except for http, mysql and few other ports. Moreover, it redirects all mysql and 13000-13004..etc port connections to a specific local ip in the same port, which is 192.168.1.100. But what I find strange is that when my firewall is active, it blocks absolutely all the input connections, even those which must not block (http, mysql). In fact, I'm literally blocked and I can't establish any external connection. What am I doing wrong? PS: I tested the firewall without those redirections, and it still block all inputs, so I suppose it's not the problem.