Mail smtp using PAT instead of static NAT assigned

Answered Question
Mar 10th, 2008
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All, I am seeing some odd things in relation to how our smtp gateway is sending information out across the Internet. When I do a show xlate it shows that it is using the global PAT of our primary ISP. However, I have a static NAT assigned to it over our second ISP. When emails are sent to external email systems from us, it is showing it coming from our smtp gateway as the global PAT assigned on my primary ISP. Is there any specific way I can watch what's going on when the firewall does a NAT with a specific command on the ASA?

Correct Answer by brettmilborrow about 9 years 3 months ago

Hi,


I think you may find that routing is what is causing what you are explaining. i.e The destination of the connection you are describing means that the traffic exits via the primary ISP link which (for your mail server) only has a PAT to the firewall interface address.


In order to verify this, you can check the routes manually using the 'sh route' command, or you can trace the path a packet would take through the firewall device using the 'packet-tracer' command, paying specific attention to the last section.

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Correct Answer
brettmilborrow Mon, 03/10/2008 - 16:36
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Hi,


I think you may find that routing is what is causing what you are explaining. i.e The destination of the connection you are describing means that the traffic exits via the primary ISP link which (for your mail server) only has a PAT to the firewall interface address.


In order to verify this, you can check the routes manually using the 'sh route' command, or you can trace the path a packet would take through the firewall device using the 'packet-tracer' command, paying specific attention to the last section.

Steve Graham Tue, 03/11/2008 - 13:17
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That was exactly what I needed, the packet-tracer command got me what I needed to resolve my issue.


Thanks for the post.

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