Good to hear that Kerio 2.1.5 doesn’t expire. The engine in that version of Kerio, which came originally from Tiny Personal Firewall, is very stable and thoroughly debugged. It should not be necessary to update it until at least the next version of Windows. For now, although not easy to get to from the Kerio web page, Kerio still has the version available at:

http://www.kerio.com/dwn/kpf/kerio-pf-2.1.5-en-win.exe

and I assume that others will make this freeware version available if Kerio pulls the link. It is an outstanding firewall and works great with Avast