problem seeing NDS tree through PPTP tunnel

Archived from groups: comp.dcom.vpn (More info?)

I am able to establish a PPTP tunnel, can ping Netware Servers (Ver. 5.1
w/SP7e) and Windows workstations inside the firewall, and can open the
management portal through a browser to the Netware servers, but I cannot see
the NDS tree or login using the Netware Client (I've tried clients for XP
Pro 4.83 SP2 and 4.9 SP1).

One interesting thing is that at school I first logged into the network
(from inside the firewall), then disconnected the ethernet cable and plugged
it into the WAN side of the firewall after changing to an available public
IP address on the workstation. I then used the PPTP connection to tunnel
through the firewall and could see mapped drives and manipulate files on the
Netware Servers from outside the firewall using Windows Explorer. However
as soon as I logged out, re-established the tunnel and tried to log back
into the Netware servers using the Novell Client (4.9SP1), no NDS Tree and
inability to log in.

I have tried the tunnel using both the same subnet as the internal network
(10.x) and a different one (192.x) with the same result.

My laptop is running XP Pro tunneling (PPTP) through a Fortigate-200 at the
school. I can VNC to Windows hosts as well.

Anyone have any suggestions?