I ran into a problem today where a Server 2008 R2 FTP Server was working fine internally, but when you tried to access it from the internet it would not work. I checked the firewall rules, in this case a Sonicwall NSA, and the NAT and firewall rules were created properly, and they were passing traffic, but the connection was still failing.
The problem appears to be on the windows firewall, for some reasons the traffic is not making it through the windows firewall. Here is how we resolved the problem:
- Create a new Firewall in the Windows Firewall
- Allow a Program through the firewall, c:\windows\system32\svchost.exe
- Allow this rule for all traffic types, Public, Domain, Private
- Give the rule a name and click Finish.
- Now test again externally and you should be able to access the FTP site.