My organization has a ISA Server 2006 as a firewall, working with two interfaces, internal and external. We have internal computers establishing VPN connection with other external VPN servers, but when the other VPN end is a Zyxel router/firewall, the VPN can not be established, showing error 619 on the origin (the Windows XP computer trying to establish a PPTP VPN). If we stop the ISA Server and configure our router to work without the ISA Server, this VPN connection is established without problem. We allways use NAT.
Any idea about what's happening with ISA Server?
Thanks in advance.