Long time ago I wrote some code to support SET/ACK IKE Mode Config for isakmpd when acting as responder, i.e. VPN-gateway et.al., which has not been completly functional, because of some strange side-effect in isakmpd. Today due to "inspiration" by Clemens Draschl and Ralf Hornik I've tested the code with a recent CVS version of isakmpd and it worked! Get the patch!