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I want to set up a simple unencrypted tunnel between a linux-server (running SLES9) and a client (running XP SP3). The reason for this is that there are many network devices in between and the client does build up many many IP connections. I want to test, if the process of building up these connections is the core of massive latency problems with this application. (There is a WAN between server and client).

Now the question: There are a lot of howtos on how to set up GRE tunnels (which seems appropriate here) on linux and cisco.

But how do I set up a GRE-tunnel on the XP-client?

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up vote 1 down vote accepted

The Windows GRE tunneling functionality is all wrapped up in the PPTP VPN client. There isn't a way to create a simple GRE tunnel interface like you can in other operating systems. You'll need a PPTP server on the Linux side to terminate the PPTP/GRE tunnel from the Windows XP machine.

I'm not sure I understand why you want a tunnel between the client and the server or how it's going to help you. You should be able to diagnose latency problems, at least in part, by capturing the traffic on the Linux end with something like tcpdump or on the Windows end with something like Wireshark and looking at the round-trip times on the TCP handshakes.

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I know that the RTT is already bad. My suspicion it that this is due to all the devices that have to build up the ip connection. Within a tunnel these devices would just "see" an established connection - they do not have to establish a new one - that should be happening inside the tunnel - i.e only on the "ends" of the connection. – Nils Nov 24 '11 at 21:25

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