VPN practical tips
This Howto gives practical examples regarding using VPN and making connections to remote servers and workstations.
Please refer to seperate Howtos for configuration of the VPN client on Windows 2000, XP and other workstations
For basic troubleshooting refer to entries made in the log file /var/log/messages at the time the VPN connection was being established
For advanced troubleshooting techniques see http://pptpclient.sourceforge.net/howto-diagnosis.phtml
VPN uses TCP port 1723 and protocol 47 (GRE).
In server & gateway mode your modem should be configured in bridged mode and automatically forwards all traffic to the server.
In server only mode, your router must be configured to forward TCP port 1723 to your server and must provide full support for protocol 47. Note that protocol 47 (GRE) is not a port and therefore you cannot forward it. Not all routers support this protocol so VPN is not always possible in this network arrangement. In order to make pptp type VPN connections in this network arrangement, the router specification must clearly say that it can handle passthrough pptp VPN connections. Note that the routers at both the remote and local ends of the VPN pptp connection must be able to handle pptp VPN passthrough for this scenario to work correctly. Check your router specifications carefully. Errors in your log files may indicate that one of your routers may have a problem forwarding GRE packets. If you see LCP timeout errors in your log files, there are many possible reasons. The most likely one is that a firewall somewhere between the two ends is blocking/dropping GRE packets. Some routers/gateways automatically forward GRE when required, by watching the negotiation on TCP port 1723.
In any point to point VPN connection, there will be numerous pieces of equipment that the signal passes through eg corporate firewalls, additional routers/firewalls, software firewalls/filters etc. All these steps in the chain must support protocol 47, if any piece of equipment in the chain does not support that protocol then the VPN connection will be unsuccessful. Sometimes these matters are out of the end users control, especially in corporate situations, or home user situations where low end broadband connections are used and ISP's limit functionality.
If you have a modem and a router between your SME server and the Internet, keep in mind that you need to open TCP port 1723 on both devices, and they must both support the protocol 47 (GRE).
You cannot establish a VPN passthrough connection through an SME server to a local machine due to problems with the sme server supporting the passthrough of protocol 47 (GRE).
VPN connections to workstations will run very slowly. It is not advisable to run programs across VPN connections, even with fast broadband Internet speeds. This applies to scenarios where a VPN connection is established to a sme server, and then a connection is made to a workstation on the remote network.
Check that the VPN user(s) in server-manager User panel are allowed VPN access
Check that the "Number of pptp clients" in the "Remote access" panel in server manager, is set to more than zero
Check that the connection is set to "Negotiate multi-link connections" in the Windows VPN client setup
Check that the VPN connection/service is allowed access through a personal firewall on Windows workstations
Please read the sections of the SME server manual that relate to VPN
For further information please also search the forums and bugzilla for numerous reports of localised and other issues using VPN
Workaround for Appletalk issue
Try this workaround to resolve issues with Kernel Panic errors, Appletalk and VPN disconnection problems
config setprop atalk status disabled signal-event reboot
Refer to these bugs
Mapping Ip addresses
to map a user to a fixed ip address do
db accounts setprop username PPTPIP xxx.xxx.xxx.xxx signal-event remoteaccess-update
where xxx.xxx.xxx.xxx is a local ip
Establishing connections & drive mapping
After establishing a VPN connection with the sme server, users then need to connect to shares
to map a ibay do
net use N: \\serverIP\ibayname
net use N: \\servername\ibayname
to see all server shares do
to connect to a workstation C: or D: drive (that has been shared in Windows) do
net use W: \\workstationIP\c
IPSec network to network VPN
For establishing a permanent VPN connection between networks see http://wiki.contribs.org/Ipsec
OpenVPN is an alternative way to provide remote access to users from home or on the road, and completely replaces the PPTP VPN which is a part of the standard SME distribution. This method may suit users who experience connection reliability issues using the standard PPTP VPN.
Also see: http://www.openvpn.net
Remote Desktop Protocol (RDP)
A good alternative to access workstations behind a SME server on a remote network, is Remote Desktop Protocol (RDP). It uses encrypted connections, is fast and flexible.
In use, forward a chosen port (say 2345), either in the port forwarding server manager panel (sme in server gateway mode) or in your router (sme in server only mode), to port 3389 on a workstation, which will allow direct RDP access to that workstation using a URL like http://yourdomain:2345
This generic technical troubleshooting diagnostic guide, http://pptpclient.sourceforge.net/howto-diagnosis.phtml while not sme specific, will assist to diagnose connection problems related to VPN pptp with SME server.