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I've setup the ufw firewall for my Ubuntu server on linode as follows:

Lish terminal info

Note that this is in the Lish terminal, unfortunately as soon as I turn on the ufw, I cannot:

  • view my test website via port 80 from browser, or even curl -I to get its response headers;

  • I cannot ssh to the server, even port 22 is "allowing access";

The default action for ufw is denying, which I believe is good practice for a "defensive" firewall. I am new to system admin stuff so I am not very sure which part I've done wrong...

Any thoughts?

UPDATED as suggested: Here are the print outs from iptables-save:

# Generated by iptables-save v1.4.4 on Tue Dec 14 09:55:24 2010
:INPUT ACCEPT [80376:49275670]
:OUTPUT ACCEPT [39230:5028423]
# Completed on Tue Dec 14 09:55:24 2010
# Generated by iptables-save v1.4.4 on Tue Dec 14 09:55:24 2010
:PREROUTING ACCEPT [81286:49365430]
:OUTPUT ACCEPT [39230:5028423]
# Completed on Tue Dec 14 09:55:24 2010
# Generated by iptables-save v1.4.4 on Tue Dec 14 09:55:24 2010
:OUTPUT ACCEPT [2334:168647]
# Completed on Tue Dec 14 09:55:24 2010
# Generated by iptables-save v1.4.4 on Tue Dec 14 09:55:24 2010
:PREROUTING ACCEPT [81286:49365430]
:INPUT ACCEPT [81274:49361314]
:OUTPUT ACCEPT [39230:5028423]
:POSTROUTING ACCEPT [39230:5028423]
# Completed on Tue Dec 14 09:55:24 2010
# Generated by iptables-save v1.4.4 on Tue Dec 14 09:55:24 2010
:INPUT ACCEPT [713:54735]
:OUTPUT ACCEPT [666:62866]
:ufw-after-forward - [0:0]
:ufw-after-input - [0:0]
:ufw-after-logging-forward - [0:0]
:ufw-after-logging-input - [0:0]
:ufw-after-logging-output - [0:0]
:ufw-after-output - [0:0]
:ufw-before-forward - [0:0]
:ufw-before-input - [0:0]
:ufw-before-logging-forward - [0:0]
:ufw-before-logging-input - [0:0]
:ufw-before-logging-output - [0:0]
:ufw-before-output - [0:0]
:ufw-logging-allow - [0:0]
:ufw-logging-deny - [0:0]
:ufw-not-local - [0:0]
:ufw-reject-forward - [0:0]
:ufw-reject-input - [0:0]
:ufw-reject-output - [0:0]
:ufw-skip-to-policy-forward - [0:0]
:ufw-skip-to-policy-input - [0:0]
:ufw-skip-to-policy-output - [0:0]
:ufw-track-input - [0:0]
:ufw-track-output - [0:0]
:ufw-user-forward - [0:0]
:ufw-user-input - [0:0]
:ufw-user-limit - [0:0]
:ufw-user-limit-accept - [0:0]
:ufw-user-logging-forward - [0:0]
:ufw-user-logging-input - [0:0]
:ufw-user-logging-output - [0:0]
:ufw-user-output - [0:0]
-A ufw-after-input -p udp -m udp --dport 137 -j ufw-skip-to-policy-input 
-A ufw-after-input -p udp -m udp --dport 138 -j ufw-skip-to-policy-input 
-A ufw-after-input -p tcp -m tcp --dport 139 -j ufw-skip-to-policy-input 
-A ufw-after-input -p tcp -m tcp --dport 445 -j ufw-skip-to-policy-input 
-A ufw-after-input -p udp -m udp --dport 67 -j ufw-skip-to-policy-input 
-A ufw-after-input -p udp -m udp --dport 68 -j ufw-skip-to-policy-input 
-A ufw-after-input -m addrtype --dst-type BROADCAST -j ufw-skip-to-policy-input 
-A ufw-after-logging-forward -m limit --limit 3/min --limit-burst 10 -j LOG --log-prefix "[UFW BLOCK] " 
-A ufw-before-forward -j ufw-user-forward 
-A ufw-before-input -i lo -j ACCEPT 
-A ufw-before-input -m state --state RELATED,ESTABLISHED -j ACCEPT 
-A ufw-before-input -m state --state INVALID -j ufw-logging-deny 
-A ufw-before-input -m state --state INVALID -j DROP 
-A ufw-before-input -p icmp -m icmp --icmp-type 3 -j ACCEPT 
-A ufw-before-input -p icmp -m icmp --icmp-type 4 -j ACCEPT 
-A ufw-before-input -p icmp -m icmp --icmp-type 11 -j ACCEPT 
-A ufw-before-input -p icmp -m icmp --icmp-type 12 -j ACCEPT 
-A ufw-before-input -p icmp -m icmp --icmp-type 8 -j ACCEPT 
-A ufw-before-input -p udp -m udp --sport 67 --dport 68 -j ACCEPT 
-A ufw-before-input -j ufw-not-local 
-A ufw-before-input -s -j ACCEPT 
-A ufw-before-input -d -j ACCEPT 
-A ufw-before-input -j ufw-user-input 
-A ufw-before-output -o lo -j ACCEPT 
-A ufw-before-output -m state --state RELATED,ESTABLISHED -j ACCEPT 
-A ufw-before-output -j ufw-user-output 
-A ufw-logging-allow -m limit --limit 3/min --limit-burst 10 -j LOG --log-prefix "[UFW ALLOW] " 
-A ufw-logging-deny -m state --state INVALID -m limit --limit 3/min --limit-burst 10 -j RETURN 
-A ufw-logging-deny -m limit --limit 3/min --limit-burst 10 -j LOG --log-prefix "[UFW BLOCK] " 
-A ufw-not-local -m addrtype --dst-type LOCAL -j RETURN 
-A ufw-not-local -m addrtype --dst-type MULTICAST -j RETURN 
-A ufw-not-local -m addrtype --dst-type BROADCAST -j RETURN 
-A ufw-not-local -m limit --limit 3/min --limit-burst 10 -j ufw-logging-deny 
-A ufw-not-local -j DROP 
-A ufw-skip-to-policy-forward -j DROP 
-A ufw-skip-to-policy-input -j ACCEPT 
-A ufw-skip-to-policy-output -j ACCEPT 
-A ufw-track-input -p tcp -m state --state NEW -j ACCEPT 
-A ufw-track-input -p udp -m state --state NEW -j ACCEPT 
-A ufw-track-output -p tcp -m state --state NEW -j ACCEPT 
-A ufw-track-output -p udp -m state --state NEW -j ACCEPT 
-A ufw-user-input -p tcp -m tcp --dport 23 -j DROP 
-A ufw-user-limit -m limit --limit 3/min -j LOG --log-prefix "[UFW LIMIT BLOCK] " 
-A ufw-user-limit -j REJECT --reject-with icmp-port-unreachable 
-A ufw-user-limit-accept -j ACCEPT 
# Completed on Tue Dec 14 09:55:24 2010
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Could you run sudo iptables-save in Lish, and then update your question with its output? –  Steven Monday Dec 13 '10 at 16:21
@Steven Monai: updated the output. To be frank I am not very fond of the "not-so-human-readable" iptables so I chose ufw in the hope that it would help me setup firewall... but it seems not configured right at the moment. –  Michael Mao Dec 13 '10 at 23:08
Looking at your iptables-save, it does not seem like any traffic would be blocked by that configuration: All built-in chain policies are to ACCEPT (except FORWARD chain on filter table, but that's irrelevant on a box that's not a router), none of the user-defined chains are referenced anywhere, and there are no DROP or REJECT targets anywhere. Sorry, I am at a loss to explain why your web and ssh requests would be blocked by this. –  Steven Monday Dec 14 '10 at 2:46
@Steven Monai: you should have made your comment as an answer so I can get you the tick :) –  Michael Mao Dec 14 '10 at 3:40
Taking a closer look at your iptables-save, it seems I spoke a little hastily. There are a few DROP targets in there. However, there is no way that any of them would be reached, as they are all in user-defined chains that are not referenced. And, please, I implore you: don't assign a tick to an "answer" that doesn't solve your question! Someone out there might have the true solution, and you don't want to discourage them from posting it. –  Steven Monday Dec 14 '10 at 4:02
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3 Answers

up vote 1 down vote accepted

If I were you I would seriously consider using something like the the iptables firewall generator to make your rules, I spend two days trying to use iptables as a router and after using this site i got it working in 5 mins.

Heres the link: http://easyfwgen.morizot.net/gen/

Hope that helps, RayQuang

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I dump ufw and use Shorewall instead. It is installable as a package. The /usr/share/doc/shorewall/examples directory has good starting configurations. It is will documented both on the Shoreline Firewall site and in the shorewall-doc packagage.

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May be your iptables-save is incomplete here?

If you run iptables-save - it dumps current rules. To make actual ufw rules current - you should run after configuring ufw:

# ufw enable
# /lib/ufw/ufw-init restart

Mine rules indeed contained a chain, that preventd all input traffic to pass:

-A INPUT -j ufw-before-input
-A ufw-before-input -j ufw-not-local
-A ufw-not-local -j DROP

which dropped all input traffic: input => ufw-before-input => ufw-not-local => DROP

i managed to fix that by modifying /etc/ufw/before.rules: comennt out this line

 -A ufw-before-input -j ufw-not-local
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