Sources:
https://www.linksysinfo.org/index.php?threads/tomato-and-ipsec-why-not.38344
https://gist.github.com/dferg/50c378701a192bc8ce6a (Requires a Github account).
https://openlinksys.info/forum/viewthread.php?thread_id=20790 (In Polish. Google translator may help).