PPTP from Windows XP/Vista to Linux fails
mppe_decompress[1]: osize too small! (have: 1400 need: 1401)
This message from dmesg familiar? The PPTP connection works fine using ping, until you try to send or receive a packet near the MTU?
It’s a bug in older versions of the linux kernel’s PPTP support. You can update your kernel to the latest version, and this problem will go away, or as a temporary solution, you can manually specify a lower MTU in windows. Note that using pppd’s options to achieve this won’t work.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters\Protocols\0]
"ProtocolType"=dword:00000800
"PPPProtocolType"=dword:00000021
"TunnelMTU"=dword:00000514
With this simple .reg file, you can lower the windows MTU, and get successful connections. This is especially useful if you can’t upgrade the kernel for one reason or another.
Sybren:
Do you know in which Linux kernel version this is fixed?
20. March, 2007, 19:13Lukas Beeler:
Not exactly, no.
20. March, 2007, 20:05Shane:
I’m having this same “osize too small” problem too on 2.6.20.
11. April, 2007, 21:54Sybren:
Hmmm… seems like it isn’t fixed in the Linux kernel after all. Shame, since I’d like to be able to connect to my office VPN :(
12. April, 2007, 08:29gev:
Thanks for article, it solves my problem
8. June, 2009, 17:34