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Firewall address shows instead of mail server address when NAT'ing?

I sure hope someone can help with this. The problem is that some mail servers see my firewall's IP address as the address of the incoming SMTP connection when my mail server tries to send mail to them.

My mail server is behind my firewall with an internal IP. The firewall (a Cisco 1841) is performing static NAT for the internal IP to a valid public IP.

Under what circustances would the destination of my connection see my mail server's IP as the firewall's IP?


Re: Firewall address shows instead of mail server address when N

If you only have a single public ip then it is working as designed.

If you have multiple ips and your firewall is one and your mail server is another then you either have a bug or a issue with your nat configuration.

If you have a simple static one to one nat with no port numbers it should work. If you have used port numbers in your static nat verify that the outgoing session from the server is actually using those port numbers as its source. I assume you are natting other types of traffic to the firewalls public ip. The router may be letting this traffic go to this default pool becauase it cannot match it to the more specific one.

You best bet is to turn on NAT debugging. Even without the debug you should see entries in the NAT table (SHOW IP NAT TRANSLATION) that show the invalid nat entry.

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