[SOLVED] VPN connectioin error: short read (-1): Message too long

If you encounter the following error during VPN connection:

pptp[12549]: nm-pptp-service-12543 warn[decaps_gre:pptp_gre.c:331]: short read (-1): Message too long

there's an easy fix. You have to lower your MTU (automatically obtained value was invalid).

First, you have to locate your VPN gateway address in syslog:

NetworkManager[11926]: <info> VPN Gateway: X.X.X.X

Then, you have to check minimum MTU toward this address:

$ traceroute --mtu X.X.X.X
traceroute to X.X.X.X (X.X.X.X), 30 hops max, 65000 byte packets
1  192.168.43.1 (192.168.43.1)  4.309 ms F=1380  4.042 ms  2.535 ms
2  * *^C

Then you have to change MTU it in your primary connection settings (network manager on Ubuntu below):



That's all!. No more spurious disconnects!