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I've got a TMG 2010 Standard server. Using the Web Proxy works brilliantly, however the server just does not seem to NAT any requests.

The clients all have the TMG box set as their default gateway ( and the network rules are almost straight out of the box, so I can't see any reason why NAT wouldn't work:

TMG 2010 will not NAT

Any suggestions on how I can get NAT working via TMG?

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Never used TMG, but do you have a packet filter rule to go along with your NAT setup? What's the value of "Default IP Address"? You could try plugging a hub and a laptop into the outside interface of TMG and run wireshark to see if anything's getting out (and possibly NATing as the wrong IP). – gravyface Aug 18 '10 at 3:40
@Gravyface, at the exact time you were posting that message, I discovered you were 100% correct - there was a packet filter rule that was screwing it all up. – Mark Henderson Aug 18 '10 at 3:43
up vote 0 down vote accepted

So, it turns out there was a "Fat Finger" rule that had accidentally denied HTTP, HTTPS and DNS access from a certain subnet. I found it after just plodding around investigating every single setting (it only took 3 hours).

So, lesson learned: If TMG will not NAT, it's probably a firewall rule that's blocking access from your subnet.

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