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I'm starting a VPN connection using Network Manager. Once the connection is established I have to change MTU in order it to work properly. For example:

sudo ifconfig ppp0 mtu 777

It is very annoying to execute this command every time I open a VPN connection. Is there any idea to create a script that would execute this command automatically once the connection is established (ppp0 interface is up)?

Peter Mortensen
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Andreas
  • 113

2 Answers2

16

Create a script in /etc/network/if-up.d, containing 

#!/bin/sh

if [ "$IFACE" = "ppp0" ]; then
    ifconfig ppp0 mtu 777
fi

and make it executable.

Community
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enzotib
  • 93,831
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    Two points: 1) the device name is probably "vpn0" these days, and 2) make sure that the filename of the script does not have a "." in it (https://bugs.launchpad.net/ubuntu/+source/debianutils/+bug/38022) – lord_nimon Jul 10 '20 at 00:33
  • This does not seem to work for ubuntu 20.04 – CutePoison Nov 09 '20 at 20:02
  • Worked for me in Ubuntu 20.04; I had to do this because openconnect --mtu 1200 nor --base-mtu 1200 had any effect with a Pulse Secure VPN. – Ingo Karkat Jan 21 '21 at 10:39
3

Here's a modernized (using ip instead of ifconfig) and generic (openconnect on the command-line uses tun0, Network Manager uses vpn0 through the network applet; the numbers may vary if another network is already active) variant of @enzotib's excellent answer, tested on Ubuntu 20.04:

#!/bin/bash

if [[ "$IFACE" =~ ^(tun|vpn)[0-9] ]]; then
    ip link set "$IFACE" mtu 777
fi
Ingo Karkat
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