Because security/vpnc is a userland implementation of IPSec, you must disable either one or two sysctls, per the installation message:
Code:
In order for vpnc to actually get any received IPsec packet, you have
to disable ESP in your kernel like this:
sysctl net.inet.esp.enable=0
If you are behind a NAT gateway, you have to disable UDP encapsulation
as well:
sysctl net.inet.esp.udpencap=0
This port has been discussed on the ports@ mailing list several times over the last five years:
http://marc.info/?l=openbsd-ports&w=2&r=1&s=vpnc&q=b