AD server does not respond to LDAP bind requests even though everything is configured fine?
Check if server has installed security update
KB3161949
This basically sets server not to respond NBSTAT to external network.
You can change the behavior using this little change using CMD
reg add "HKLM\System\CurrentControlSet\Services\NetBT\Parameters" /v "AllowNBToInternet" /t REG_DWORD /d 1 /for using PowerShell
Set-ItemProperty -Path HKLM:\SYSTEM\CurrentControlSet\Services\NetBT\Parameters -Name AllowNBToInternet -Type DWord -Value 1
After change is applied, you have to reload the server.
Little more background
here
Regards,
Ondrej