VPN and Remote Desktop Issue

Hi All,
1st post and already off topic!  Well, I am sure you all agree, the life of the PBX Engineer rapidly became the life of network and server engineer some years ago.
As a business we all work from home or work while on the road and can be called on at any time to make a connection onto someone's phone system and make changes.  Of course a dial up connection using a modem onto an older system when you are in a car park on the motorway is not possible, so we came up with a solution.
Each principle engineer has a Virtual XP machine hosted on a VMWare server in our office, and we all have a Hamachi software VPN into the office. So long as we can get onto the internet we can remote desktop to the XP machine and do all we need to do.
However I have found the Hamachi VPN to be painfully slow at times, especially if you want to transfer files from home to the office. - My solution?  Since I had just fitted a VPN router at home, I decided to put in a tunnel between home and the office. this should at least speed things up when I am at home.

So that's what I did. Found some instructions and created a tunnel. I could ping fine, I could open files on the server and browse to the internal database.  What I couldn't do was remote desktop to my hosted machine!

I searched the internet and checked if others had the same problem, and after an hour came up with nothing. If I disabled the tunnel and enabled Hamachi, remote desktop worked. If I went back to the tunnel, no remote desktop.  The mad thing was that the XP machine could control my windows 7 laptop at my house, so it was only in 1 direction that RDP didn't work.

I finally checked to see if the XP machines firewall was on. It was and could not be turned off due to group policy. I checked if I could remote desktop from another machine in the office to the XP machine and I could.  Then I had the lightbulb moment.

Hamachi uses the DHCP server on your network to give your machine a LAN IP address. however the tunnel I had setup was LAN to LAN so my machine at home was on a different network to the XP machine. The firewall policy allowed connections from the local LAN but not from a foreign LAN.

Having figured this out, and not having seen the solution online, I thought I would post it to assist others who may come across the same.

John Rogers
Telecom Care Ltd