Often we have to troubleshoot routing and firewall rules as seen from a client on a internal client subnets. I use PSEXEC and PORTQRY from Microsoft. This will work if it is a Windows pc and I have permissions to connect to it. Run these commands from a server in the server lan
I try to check if the port is open from the client to server (10.10.10.100) :
Are you looking for a replacement for TMG now that its end is nearing. You could buy a thirdparty reverseproxy from Sophos og some appliance. The simplest solution is probably to install a Windows server 2012(R2) and add ARR module to IIS.