Ultravnc over vpn issue

[Nirodh]

Good day all

I am new to this forum. I am also new to networking. I am employed at a Packaging Manufacturing Company in South Africa. The owners have purchased a new machine which is managed through a PC running Windows XP. The manufacturers of the machine (from Taiwan) need to be able to connect to the machine in order to configure and troubleshoot problems. They have insisted on using UltraVNC-100-RC18. I have setup a VPN through which they connect and do whatever needs to be done to sort out problems with the machine settings. The VPN works fine. I had initially set it up in December but for some reason they are unable to connect to the Ultra VNC server. Then weirdly enough in January they were able to connect without me changing any settings. But this week they are unable to connect again. From within the network I am able to connect to the VNC server instantly. I tried myself to dial in through a separate VPN and connect to the Ultra VNC server but am not able to. All settings on the VNC software is default( port 5900,etc). I am able to ping the machine through the VPN as well as 2 PLC's within the machine with no problems. I can connect through the VPN with Remote desktop as well but just cannot connect to the Ultravnc Server on the Xp machine. I have also tried disabling antivirus/firewall on the VPN Server just incase and even uninstalling but that did not work either.

Any help will be greatly appreciated. I am still newbie to networking. What could the problem be?

Thanking you in Advance

Nirodh

[Nirodh]

Good day all

Just an update to my issue with Ultravnc over VPN. This morning I had a problem with our internet connection so I had to reset the modem (Netgear N300 wireless - DGN2200Mv2). Upon doing so the internet connection came back online and I tried to connect with Ultravnc viewer to the XP machine through the VPN, and to my surprise it connected! This is very strange yet also annoying. The main reason being that i had reset the modem at least 4 times yesterday thinking it had something to do with the modem. The MTU size on the modem is set to 1492. I have read on a few posts online that the more devices a data packet is routed through, then the data packet size is changed because of the routing info that gets added on to it. Do not know if this had something to do with my problem. I assume that each time I reset the modem the actual route that the data packets take to reach my network changes until it reaches the least number of devices so that very little routing info gets added on hence not changing the actual info required for the VNC server to negotiate a connection. Do not know if that makes sense to anybody out there. Do not know if this is correct. Hopefully this connection is maintained everytime I need to connect.