Red Hat Bugzilla – Bug 1302654
NetworkManager PPTP connection terminates
Last modified: 2016-12-20 13:15:49 EST
NetworkManager-pptp-1.1.0-2.20150428git695d4f2 on Fedora 23. The problem has been seen on two different machines so far.
NetworkManager PPTP connections to a Microsoft VPN server (which works reliably with other clients) are suddenly terminated. Usually what triggers this is transferring large files using scp, but when the connection is made through a phone using it as a mobile hotspot it happens almost immediately when using the connection at all.
When the connection is terminated the log contains
Jan 28 11:14:06 localhost.localdomain pptp: nm-pptp-service-5233 warn[decaps_gre:pptp_gre.c:347]: short read (-1): Message too long
Jan 28 11:14:06 localhost.localdomain pptp: nm-pptp-service-5233 log[callmgr_main:pptp_callmgr.c:245]: Closing connection (unhandled)
Jan 28 11:14:06 localhost.localdomain pppd: Modem hangup
Judging from other bug reports this could have something to do with the MTU of the internet connection, which using the mobile is 1410. I have tried setting the MTU of ppp0 (when activated) to 1400, but that doesn't seem to make any difference; the connection still drops immediately.
This seems similar to another VPN issue logged: 1293074. Do you have the same issues if you run it with netfilter.nf_conntrack_helper?
sysctl -w net.netfilter.nf_conntrack_helper=1
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