janjust wroteI can't even ssh from c2 to itself via any of the IPs listed by ifconfig.
if this is true then it's not openvpn related at all; if a simple 'ssh 127.0.0.1' does not work then you need to fix this first.
Thanks for the reply.
I guess I will need to take the issue to a VirtualBox forum then, because 'ssh 127.0.0.1' in fact fails to work on the Linux that's running under VirtualBox.
(An addition to the original post: ping among _any_ pair selected from {c1,c2,server}, in any direction, does work.)