I have a Windows 2003 SBS with ISA 2000 set up as a VPN Server. I have a Windows XP Pro client that is connecting through to it. It seems that after only a few minutes, the VPN connection is ended without any error messages. I am using PPTP and certificates for authentication.
I have checked Remote Access Policy settings regarding limits/idle times etc. and they all seem ok. I have tried connecting the vpn and then running a constant ping to the VPN server, but it still disconnects. I have tried two different client pc's, both running Windows XP Pro. The Windows 2003 server sits behind a Netgear DG834 DSL Modem/Firewall that has the latest firmware. It is passing all traffic for PPTP onto the external IP of my SBS. I found a solution on this site that suggested reducing the MTU in the DG834 from 1500 to 1460. I also tried doing this on my XP computer with the help of TCPOptimiser. None of what I have done above has made any difference whatsoever.
I have spent quite a few hours researching this problem but have been unable to fix it so far. I would appretiate any help that can be offered.