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Exchange 2003/DC subnet change

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  • Exchange 2003/DC subnet change

    I don't even know where to start. I am very very new to all of this.

    We had a firewall crash (hardware failure) which is out of warrenty (by days), so to replace the exact device to reload the config backups is finacially out of the question at this time. So to temporarily make due I am trying to reroute everything through our netopia dsl router. Here is where my issues begin.

    The DC/Exchange server(Win2k3 Server R2 fully updated) is the dns/dhcp server on subnet. Our Public IP routes to the Netopia DSL Router( which then changes this ip to and this traffic goes to our firewall( which then changes the ip to the domain controller/exchange server.
    (maybe changes is the wrong word route may be better and i apologize for any misunderstandings)

    without the firewall there i attempted to change all the dns for the exchange server to send and receive mail based on the ip

    I set the netopia as the dns server on the DC, and assigned all pc's on this network to the same subnet, they are all now able to access the internet, authenticate to the network and send mail, although no mail will come into the server.

    i used this hxxp:// online port scanner to verify connectability to smtp 25. I am also able to connect via remote desktop to my dc/exchange server using the public IP. I have checked and changed everything google has told me to do for the past 4-5 hours. If there is any information i can provide that i neglected to include please ask as i would like to resolve this as soon as possible.

    It appears that although the port is open, once you try to connect via telnet i get the following:

    [email protected] ~ $ telnet 25
    Connected to
    Escape character is '^]'.
    Connection closed by foreign host.

    it allows connection then immediatly disconnects? since this discovery i have read many more things and have made a few changes. Setting the dns server for the dns/dc/exchange server to

    didn't seem to help nor harm anything..... at least i know what the issue is, now i just need to resolve it, any ideas?
    Last edited by skeptik; 4th February 2010, 04:32. Reason: further troubleshooting

  • #2
    Re: Exchange 2003/DC subnet change

    After reading more and more, i've installed wireshark and filtered "dst port 25" and then attempted to connect via telnet from a remote machine, it pushes out 6 packets, i have no idea how to read this, it may be helpful in resolving my issue.

    too large to paste, check attachments
    Attached Files


    • #3
      Re: Exchange 2003/DC subnet change

      Do you not have sales protection laws where you are? Here in the UK, the warranty on an item means nothing - if the device fails after 18 months I can demand the manufacturer repairs the item (usually replaces it) because in law there is a reasonable expectation of life. If the item was 10 years old then they could tell me to go away.


      Why are you double natting - that will always cause problems. If the router can do the port control then do it there, don't put something in front of it.
      Otherwise look to see if it will pass the external IP address straight to the device behind the router, so that you can lose the interim IP address NAT.

      Check both products for SMTP scanning functionality, IP address restrictions on the SMTP virtual server etc. Verify things work internally as well.

      The internal DNS on the server shouldn't be either, it should be the server's real internal IP address.

      Simon Butler
      Exchange MVP

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