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I am trying to open up ports in CentOS's firewall and am having a terrible go at it. I have followed the "HowTo" here: http://wiki.centos.org/HowTos/Network/IPTables as well as a few other places on the Net but I still can't get the bloody thing to work.

Basically I wanted to get two things working: VNC and Apache over the internal network. The problem is that the firewall is blocking all attempts to connect to these services. Now if I issue

 service iptables stop

and then try to access the server via VNC or hit the webserver everything works as expected. However the moment I turn iptables back on all of my access is blocked. Below is a truncated version of my iptables file as it appears in vi

 -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 5801 -j ACCEPT
 -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 5901 -j ACCEPT
 -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 6001 -j ACCEPT
 -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 5900 -j ACCEPT
 -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT

Really I would just be happy if I could get port 80 opened up for Apache since I can do most stuff via putty but if I could figure out VNC as well that would be cool. As far as VNC goes there is just a single/user desktop that I am trying to connect to via: [ipaddress]:1

Any help would be greatly appreciated!

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migrated from stackoverflow.com May 18 '10 at 20:09

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3 Answers 3

up vote 2 down vote accepted

Assuming that you don't have any REJECT/DROP statements above, all you need to do for an internal network (let's say that you're on 10.1.1.x and want all hosts in that range) is a statement such as:

-A RH-Firewall-1-INPUT -s 10.1.1.0/24 -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT

and follow this for each additional port. Check the top of the file and make sure that :RH-Firewall-1-INPUT - [0:0] is present or use the standard -A INPUT instead.

! Keep in mind that iptables is processed top to bottom. !

If this doesn't work, post your whole conf or move your DROP or REJECT line to the end of the file (but above COMMIT).

Make sure to do a /sbin/service iptables reload after.

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cHao was on the right track with asking for more of the iptables. In my ignorance I was not aware that the position of an entry in the iptables mattered (although since they are chains I should of picked up on that.) Anyway the issue was that all of my lines were falling after this line:

 -A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited

Once I moved them before the above line everything worked fine.

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It looks like the rules would allow new incoming connection requests, but not data from existing connections. If you get rid of the -m state --state NEW for port 80 (the last line you listed), or add a rule for ESTABLISHED and RELATED connections to all ports, it should make port 80 available.

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Hi cHao, thanks for the quick response but that does not alter the behavior of the Cent box =\ –  abszero May 18 '10 at 20:05
    
I'm going by the info i have. If you could pastebin the whole iptables setup and post a link, or add it to your post if it's not too big, i could maybe help more. –  cHao May 18 '10 at 20:09

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