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haimat
Apprentice
Joined: 05 Sep 2002
Posts: 239
Location: Vienna / Austria
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 Posted: Tue Apr 27, 2004 10:53 pm Post subject: Problem with iptables and port-forwarding (DNAT) |
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Hi all,
I have a strange problem with my netfiler setup. First to my infrastructure: I have a firewall/gateway in front of a private network, there is a mail server. The firewall is connected to the internet via a ppp line.
Now I want to forward all incoming traffic on port 25 (SMTP) to my intern mail server. So I added the following command to my firewall script:
| Code: | | $IPTABLES -t nat -A PREROUTING -i $E_NIC -p tcp --dport 25 -j DNAT --to-destination 192.168.120.10:25 |
(I know this should work, because I have exactly the same line on other setups.)
But when I now want to test this, I get the following:
| Code: | [ 00:30 haim@itchy ~ ] telnet <pub.IP> 25
Trying <pub.IP>...
Connected to <pub.IP>.
Escape character is '^]'.
Connection closed by foreign host. |
As you all can see, my connection gets dropped as soon as it was established. When I disable the above iptables line, I get the following response from telnet:
| Code: | [ 00:19 haim@itchy ~ ] telnet <pub.IP> 25
Trying <pub.IP>...
telnet: Unable to connect to remote host: Connection refused |
(which is ok of course.)
Strange thing here is: When I do this port forwarding with the rinetd daemon, I get no errors and can connect to my mailserver fine.
So I think it's an iptables issue. Could this be because of the ppp line? Or what else is the problem here?
Greetings and TIA, Matthias |
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haimat
Apprentice
Joined: 05 Sep 2002
Posts: 239
Location: Vienna / Austria
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| Posted: Tue Apr 27, 2004 11:01 pm Post subject: |
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UPDATE: I forgot to tell you, that the mail server is an MS Exchange server. It seems it is dropping my telnet connection.
When I try to forward port 80 (HTTP) to an intern IIS server, then I get no errors and can do a "GET" request.
Hmm... damn Microsoft 
Anyway, some ideas?
Greetings, Matthias |
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