Server 2008 R2 Routing and Remote Access PPTP VPN issues

Hello,

Some of my users are having problems connecting via routing and remote access PPTP VPN, I myself never experience this issue however many users appear to be disconnecting and having to redial the VPN almost 10 times before it remains connected so they could carry on their work. Nothing obvious in event logs, any ideas what could be causing this?

Thanks,
Mark
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Nolan GustavoAsked:
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Nolan GustavoAuthor Commented:
Found warning in event log:
Failed to apply IP Security on port VPN2-113 because of error: A certificate could not be found.  Connections that use the L2TP protocol over IPSec require the installation of a machine certificate, also known as a computer certificate..  No calls will be accepted to this port.
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Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
Check if that happens more often while more than one connection is used. It sounds like an issue with GRE session IDs and NAT - in particular if there is a firewall/router in front of the server. It's always best to have the VPN device directly connected to the WAN/Internet.
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Nolan GustavoAuthor Commented:
Thanks I have enabled logging and now waiting for the connections to start dropping.
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Nolan GustavoAuthor Commented:
Qlemo, please can you clarify on the GRE session IDs and NAT comment? this doesnt seem to affect all users, I for example cannot replicate this fault however 2 users on site regulary appear to be affected by this.
I have reviewed the logs, I might be missing something but I cannot see anything obvious at this point.

Cheers
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Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
GRE is troublesome if NAT is in the way, because it is an own protocol without ports. NATting firewalls need special logic to be able to map GRE connections to multiple servers and/or clients. Usually there is no issue if only one client connects to exactly one internal server, but other than that - sporadic failures.
If it is that way, you can't do anything but to see if there is a new router/firewall firmware available. Or switch to a different VPN type.
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Nolan GustavoAuthor Commented:
Switched to different VPN type in the end (-:
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