We have a Zywall USG 300 security device (firewall) at work. I have just finished configuring for it a VPN tunnel using Greenbow IPSec software.
The problem is that it only works when I turn off the Firewall functionality of the USG 300. This indicates that the IKE and IPSec configurations are working correctly, and points to a port problem. I wouldn't have thought a firewall rule was needed, but it seems that it is. I've tried opening ports 500, 50 and 51 but to no avail.
Anyone got any ideas?