Most of the time, our VPN (L2TP over IPSec, SoftEther) works great. All the users (3 or less concurrent) can connect without problems.
Lately, we have been noticing that we sometimes can't access servers behind the VPN.
The connection to the VPN (OSX client) is established successfully, no problem. Then, randomly, trying to SSH to a server just fails (connection refused). After a few seconds (less than 20), we are able to SSH in successfully. SSH is just an example, this happens for all the services behind the VPN. The VPN connection UI indicator did not show any issues or disconnects.
This issue happens on different networks, so in theory, it's not happening because the client has internet connectivity problems.
Do you guys know what could be the cause of the issue?
Best Answer
Turns out, I had a local bridge installed and the virtual NAT enabled. For reasons that are beyond my knowledge, these two features don't play well together. I disabled my local bridge and now things are running great again.
When opened up the NAT table, I saw that it was abnormally huge. I googled this and discovered a post on the SoftEther forum about this, and someone said it was due to local bridge and virtual NAT. So I disabled the local bridge, the NAT table shrunk, and the problems were gone.