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Cisco IOS NAT U-Turn



The scenario -

Clients on the LAN use a public DNS server for their DNS; the local clients must resolve the local email servers IP address as the public IP address, which is performed through NAT. The clients can access email (OWA) when they browse the IP address, but this does not occur if they enter in the URL.

I believe the NAT is working fine, but the traffic is not getting back to the clients. I contacted Cisco and the engineer stated that the IP is being routed out the WAN interface and was the reason why clients were not able to load OWA.


Has anyone come across this scenario? Is there a way to get this to work?


Hi , Do DNS registration for

Hi ,

 Do DNS registration for NAT IP address . Thereafter client can resolve it with public IP address . 




Community Member

Could you explain a bit

Could you explain a bit further on how this would be carried out? Do you have any documentation you could point me to?

Hi Ashley, I have an idea but

Hi Ashley,


I have an idea but i am not sure if that helps.... Here you need a DNS doctoring on the IOS router to do with your requirement. But why can't you try like this...... add a hostfile entry for the specific OWA url mapped to the local LAN address..... I believe Host file entry takes the priority before it takes to the DNS for resolution. I will check on the DNS doctoring as well to do with your solution.




Community Member

Host file is an added

Host file is an added headache on the management of PCs.

Hi,Hope the below mentioned


Hope the below mentioned thread would clear your doubts. As per the thread DNS doctoring is not possible in IOS routers.... There are multiple work around suggested in this thread which might be helpful for you.




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