Hello! Yes, it works. I had accidentally disabled ESP and AH protocols in /etc/sysctl.conf (thinking I had *enabled* them by un-remarking them, instead).
NEVER configure a machine when it's too late at night. Should have known better. BTW, Hans-Joerg, the 3.8 machine is tunneling OK with the 3.6 machine, even without the -T option (looks weird, but I'm pinging...). Are you still interested in the debug output? In case, drop me a private message. Again, thanks a million. And sorry for the noise. --Rob