I have a home VPN set up (OS X's native L2TP/IPsec on a 10.13 machine). I appreciate that the recommended way to start this would be via launchctl but, accepting that I invoked vpnd directly:
sudo /usr/sbin/vpnd -d -i com.apple.ppp.l2tp
What command would stop the server? The man page for vpnd does not provide information on how to halt the server.