Arch Linux

Shtsh

Member

From: Minsk

Registered: 2012-06-25

Posts: 5

[SOLVED] NetworkManager ignores MTU size when using PPTP

I'm using PPTP to connect to my working network.
I've configured connection to use with pon/poff and it works well, but I want to use NetworkManager to manage all connections.

I created VPN PPTP connection. But after successful authentification NM drops connection with next message:

pptp[18526]: nm-pptp-service-18522 warn[decaps_gre:pptp_gre.c:331]: short read (-1): Message too long

This message usually means that MTU in PPTP connection is too large.
I've changed next options in /etc/ppp/options

mtu 1000
mru 1000

like values in the working pptp connection when using pon/poff.

Then I run

watch ip link show

and I noticed that ppp0 was created with MTU=996 (it's great!) but then MTU size was changed to 1400 (bad) and connection dropped.

So I think it's NM's fault. Do you have any ideas how to resolve this issue?

Last edited by Shtsh (2012-06-27 11:50:17)

Shtsh

Member

From: Minsk

Registered: 2012-06-25

Posts: 5

Re: [SOLVED] NetworkManager ignores MTU size when using PPTP

Resolved using http://archlinux.org.ru/forum/viewtopic.php?f=16&t=8721

# cat /etc/NetworkManager/dispatcher.d/20-mtu_change 

#!/bin/bash

INTERFACE=$1
STATUS=$2
VPN_ID="5d4ee387-3171-4006-bda1-231b249690b9"

if [ "$STATUS" = "vpn-up" -a "$CONNECTION_UUID" = "$VPN_ID" ]; then
    ip link set "$INTERFACE" mtu 1000
fi

act28

Member

Registered: 2011-07-11

Posts: 10

Re: [SOLVED] NetworkManager ignores MTU size when using PPTP

In case this helps someone else save time....

To find the connection uuid:

$ nmcli c

E.g.

NAME                   UUID                                                                     TYPE                      DEVICE
AndroidAP            e17b50d1-cbc9-4a3b-897c-0d9ae3efc33c           802-11-wireless     --
Work-VPN        d278c1df-b6f7-4efb-9af6-f9a7ee2c68ce    vpn                  --
eno1                     b967d41e-4842-4468-aa93-aeaa637eef14          802-3-ethernet     eno1

WorMzy

Administrator

From: Scotland

Registered: 2010-06-16

Posts: 12,476

Website

Re: [SOLVED] NetworkManager ignores MTU size when using PPTP

And with that, I think we can close this thread.

https://wiki.archlinux.org/index.php/Fo … bumping.22

act28, if you think that information will be particularly helpful, you may want to see if you can include in on a relevant wiki page.

Closing.

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