PPTPD Slow Performance

[jafar]

Hi guys
Just want to get some suggestions here.
For my lab, I am planning to setup a VM to be used as PPTP server (poptop daemon) on CentOS 5.
The VM and the PPTP server is up and running, but I am having a performance issue.

The PPTP server network card is setup in bridged mode using the para-virtio interface.
File transfer from and to the VM via its bridged IP address works fine. I am getting pretty close to wire speed (50MBps, I am not complaining). A 100MB file transfer takes about 2 seconds.

When I start up the VPN connection and try file transfer via the VPN interface (that is, if I do a file transfer via its VPN IP address), I am getting 1/5th of the performance. The same file will transfer in 10 seconds. Now, I am aware that VPN connection will suffer some sort of performance degradation, but I was not expecting to be that much. Can I get a suggestion here, as to what to tweak?

[Martin]

Have a look at the MTU sizes, sometimes with a VPN connection it isn't automatically detected and you need to lower the MTU size a bit so that the packages still fit in the frame.

[noteirak]

Try with the Intel 1000 MT Desktop, I encountered some issues with VPN & VirtIO adapters at times. This might help solve some issues.

[jafar]

Thanks, guys.
I was getting packet fragmentation, and lowering the MTU seems to help but not much.
The Intel card actually performs slower I find.
Anyways, I can replicate this on a physical machine (laptop) on roughly the same OS setup (CentOS), so I'll chalk it up to the package not working well and I need to troubleshoot for something else.