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How do you determine where a port is being blocked?

Posted on 2011-03-17
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Last Modified: 2012-05-11
Due to last weeks earthquake in Japan our IPL's are down.  We are trying to establish alternate connections using P2P vpn tunnels through the internet.  We have the tunnel up and everything is working except email.  Both sites are part of the same AD.  The server on that side is now passing email to teh server on this side.  However our server can not connect to thier server.  We checked and Port 25 is being blocked some where in the Tunnel.  But we can not find it.  We have examined every device that we are aware of and can not find the port blocking.  

Is there a tool that we can use that would help us identify where the port is blocked?

Is there a way to make Exchange 2007 use another port for Server to Server Communication?
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Question by:abrannon
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by:shubhanshu_jaiswal
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just disable the esmtp inspection in the firewall...
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by:abrannon
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There are no Firewalls configured on this tunnel.
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by:Ernie Beek
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Ok, how is the VPN set up then?
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cavp76 earned 500 total points
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VPN traffic is encapsulated between two points, so there's no possible way to have a firewall "in the middle" of a VPN, only at each end... check that their server is not filtering connections from your server, or in any case add an entry in the IP allow list rule to allow SMTP traffic from your Exchange IP address:
To configure an IP Allow List using the Exchange Management Console, do the following:
1. Launch the Exchange Management Console.
2. Select Edge Transport in the console tree.
3. Double-click the IP Allow List item in the action pane.
4. In the IP Allow List Properties window, select the Allowed Addresses tab.
5. Click the Add button or the down arrow and choose the IP address option to add a IP address or range .
6. Click OK to add the IP address or address range.
7. The IP addresses or address ranges are shown in the IP Address(es) section of the Allowed Addresses tab in the IP Allow List Properties window.
8. Click Apply to save changes or click OK to save changes and close the window.

Hope this helps
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by:abrannon
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This solution was on the right track.  We engaged Microsoft who also went along this path, But we never resolved teh issue.  The IPL was repaired before we resolved the problem on the temp line.
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