Enable VPN debug on macOS Sierra? I'm trying to debug a Cisco IPSec VPN issue (using native OSX VPN, not a separate client) but I can't find any options to turn on debugging.  Looking around the net it seems there was options in the Advanced tab at one point but I don't see them in Sierra.
Logging is enabled by default. The logs can be inspected using the Console app open /Applications/Utilities/Console.app. Select "Errors and Faults" and look for "neagent" lines.