“Consider a scenario where a TMG administrator has configured their TMG Server 2010 installed on a Windows Server 2008 R2 for inbound VPN connections. External VPN users (two or more users) are behind a NAT device, which NATs all outbound L2TP VPN traffic. When users try to connect using L2TP VPN connections, only one user from this network can connect at a time. Every connection attempt from another user fails with the following error:
Error message: error 809
The network connection between your computer and the VPN server could not be established because the remote server is not responding. This could be because one of the network devices (e.g., firewalls, NAT, Router etc.) between your computer and the remote server is not configured to allow VPN connections. Please contact your Administrator or your service provider to determine which device may be causing the problem.”
Pretty interesting problem and one that definitely cries for a solution!
To find the answer, check out the TMG firewall Team Blog over at:
DEBRA LITTLEJOHN SHINDER
MVP (Enterprise Security)