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could you tell me how to find out all the firewalls that are installed on my system Ubuntu 10.04 and on external hardware and which of them is blocking port 80?

thank you

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closed as off topic by RobM, MDMarra, joeqwerty, squillman, Sam Mar 28 '11 at 10:11

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To view the firewall configuration on your localhost, run 'sudo iptables -L'. If you have no control over your upstream firewalls, you will have limited ability to probe or change them. You should talk to your system/network administrator or ISP.

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Does the command 'sudo iptables -L' cover all of the firewalls that may be installed on the system? – xralf Mar 26 '11 at 19:33
"If you have no control over your upstream firewalls, you will have limited ability to probe or change them." Can I use something like ping or traceroute and see the node in the network where packets were blocked? – xralf Mar 26 '11 at 19:35
"iptables -L" shows all iptables rules active on the server. While there are many GUI and command line applications that manage firewall configurations, iptables (netfilter) is pretty much the only firewall engine on Linux that they all configure. So if you see some rules in the output of "iptables -L", then that is what you have on the server. – vadimk Mar 26 '11 at 22:07
to find if some dedicated firewall (or even router access list) blocks connects to the server you need to be able to probe it from outside. Regular ping and traceroute can't tell if tcp port 80 is blocked. Assuming your local iptables configuration does not block incoming connections, you could run tcpdump on the server to listen to such packets while you try to connect to your server. If you see no incoming packets in tcpdump output, they got blocked somewhere along the way. The command would look like "tcpdump -n tcp port 80". You still need to talk to the admin to get them remove the block. – vadimk Mar 26 '11 at 22:12

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