Putting this one here because it was driving me crazy a while back. VPNs on OS X have a tendency to disconnect when the machine goes to sleep, i.e. when you close the lid. They also tend not to notice they’ve disconnected. This is the fix (it’s for PIA, but the principle should be similar for any client).
The only reason I realised this was happening on my laptop was that I just-so-happened to be at a hacking 101 course, and so had Wireshark open all the time. I could see all the VPN connections just fine in the morning, and was wondering why they seemed to fail at around break time. I imagine there are a tonne of people out there who are also afflicted by this, but don’t happen to have Wireshark, so don’t notice, and thus blithely continue to use the ‘net, under the assumption they’re protected by their VPN, when in reality all their traffic is being transmitted in the clear and they’re leaving their local IP all over the internet.
This is the problem with security tools, though; they’re only as good as their configuration. Broken security is worse than no security at all, and all that.