MTU keeps getting reset to 1500

Question

I'm running OpenSuse Tumbleweed with gnome 3.22.

---

I need to set my MTU to 1472. If I do so with with:

ip link set mtu 1472 dev ppp0

it works:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
   valid_lft forever preferred_lft forever
inet6 ::1/128 scope host 
   valid_lft forever preferred_lft forever
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 88:ae:1d:59:7c:1a brd ff:ff:ff:ff:ff:ff
inet6 fe80::2c7:1e3d:2a85:7a43/64 scope link 
   valid_lft forever preferred_lft forever
3: wlp6s0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
link/ether 5a:37:1f:84:93:99 brd ff:ff:ff:ff:ff:ff
16: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1472 qdisc pfifo_fast state UNKNOWN group default qlen 3
link/ppp 
inet 31.176.245.43 peer 109.175.48.1/32 scope global ppp0
   valid_lft forever preferred_lft forever

But as soon as I open the NetworkManager and restart the connection I'm back to 1500...

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
   valid_lft forever preferred_lft forever
inet6 ::1/128 scope host 
   valid_lft forever preferred_lft forever
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 88:ae:1d:59:7c:1a brd ff:ff:ff:ff:ff:ff
inet6 fe80::2c7:1e3d:2a85:7a43/64 scope link 
   valid_lft forever preferred_lft forever
3: wlp6s0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
link/ether 5a:37:1f:84:93:99 brd ff:ff:ff:ff:ff:ff
17: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 3
link/ppp 
inet 92.36.220.222 peer 109.175.48.1/32 scope global ppp0
   valid_lft forever preferred_lft forever

---

I also tried editing the file /etc/ppp/options to no avail.

Setting the MTU from within the NetworkManager GUI doesn't work either.

Answer 1

OK, I couldn't find any configuration that works, but it is possible to add a dispatcher script into /etc/NetworkManager/dispatcher.d dir.

Adding something like:

#!/bin/bash

ip link set mtu 1472 dev ppp0

should do the job.

Still, this should be possible with a config file, no?

The config files under /etc/NetworkManager/system-connections don't work. They can be edited from within the GUI too.