Unusual Microsoft VPN results at one site

I'm hoping that someone may have some clues about a MS VPN problem I'm having at one site, but not at others.

I am using a couple of laptops at the offending site, each of which has a Microsoft VPN directed to the same target IP address (in fact a remote router with a fixed IP address).

Having established an ordinary internet connection on the laptop, the VPN on one laptop is started up, and it connects successfully. The same is done on the second laptop, but the VPN connection hangs for a minute or two and then fails with error 789 (if I remember correctly).

If I redefine the VPN settings on the second laptop to point to a different target router IP address, it will connect immediately.

It may or may not be relevant that the source router at this site is a BT Business Hub 5 - I don't know the source routers at other sites, but they are probably not BT ones.

At all other sites there is no problem, and two or even three VPNs can be established simultaneously from two or three laptops, each pointing to the same target IP address.

About all I can think of is that the BT Business Hub 5 has some form of limitation with regard to outgoing VPNs, but this may be a complete red herring.

Please could anyone suggest a solution, or what to do next to investigate the matter? Thanks!

Am I right in thinking that it does not matter which laptop established the first VPN connection to this particular server, it is always the 2nd laptop that has a problem?

Have you turned off port clamping on the home hub?

Also UPNP extended security can cause some issues.

Yes, it is only the second attempted start of the VPN which fails.

And we have no administrative access to any local router - they are a 'given', unfortunately, and we simply make use of the internet connection service...

In this instance, I would suspect that the BT Business Hub 5 has been installed 'as is' without anything much in the way of options setting.

Edited by John_Gray (Fri 12-May-17 18:08:14)