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Old 07-16-2009, 03:48 AM   #1
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JAMES or DNAT problem?

Hey everyone,

need experts' help!

I've got:
  • server1 - server box somewhere on the Internet
  • server2 - server with Apache James behind the Ubuntu NAT box
Here's Ubuntu's netfilter ruleset representing DNAT:
iptables -A FORWARD -d $INT_IP -i $WAN_IF -o $INT_IF -j ACCEPT
iptables -t nat -A PREROUTING -d $EXT_IP -i $WAN_IF -j DNAT --to-destination $INT_IP
I'm sure that NAT/DNAT works fine because I can access the Internet from server2 and I also can connect to James SMTP module on server2 (`telnet server2 25` is ok), but `telnet server2 110` gives a "Connection refused" error just after short delay. Why I am thinking it's an DNAT problem? I've started `nc -l 2424` on server2 and successfully telneted from server1 on port 2424, but if listening by netcat port is privieleged (i.e. `nc -l 24`) then `telnet server2 24` from server1 gives same "Connection refused" error. But still... Why 25, 80 and 443 ports are DNATed successfully?! I'm stuck.

Here's extract from James' config.xml:
   <pop3server enabled="true">
         <helloName autodetect="false">XXX.YYY</helloName>
Old 07-16-2009, 04:27 AM   #2
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Can you verify whether you can connect from behind the firewall? In otherwords, verify that the service is working.

Second. Do you know whether your ISP is blocking port 110? Perhaps change the port used temporarily for testing purposes.
Old 07-16-2009, 04:32 AM   #3
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Thanks for the tip! Looks like the problem is in server1's firewall! I'll check this and write back...
Old 07-16-2009, 07:26 AM   #4
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Yes it was server1's firewall. Sorry.



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