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UDP incorrect checksum

All,

I have a Cisco 1841 Router. I am attempting to take an internal DNS server and expose it to the Internet via port UDP 53. I have successfully wrote the NAT rules for connections inbound and have properly routed them to the internal DNS. Additionally, I have created rules in the firewall to allow the traffic both inbound and outbound.

DNS functions properly internally, but when someone attempts to access it externally, it does not work. I can see the packets coming in and all looks well. However, performing a packet capture on the machine thats external (user trying DNS), it says that "incorrect UDP checksum". To ensure it was not the DNS server, I set the server up with an external static address (directly on the Internet) and it worked fine. I am thinking it has something to do with the router and maybe specifically how the ISR is sending it back out. Any help would be greatly appreciated. I am completely stumped. Thanks in advance.

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Anonymous
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I have this issue too except

I have this issue too except it's on an ASR 1001hx on the latest version of code, this is the only article on the internet that I could find that relates to my issue .. Very weird issue 

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