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EDIT: Ubuntu bug posted here

some time ago I wrote a detailed answer to fix an error for lowering MTU size for a cisco compatible VPN.

After upgrading to Ubuntu 24.04 LTS, I'm unable with the same steps to lower the MTU size.

In particular, if I run the following command from the terminal

sudo ifconfig your_tunnel_name mtu 1370 up

it seems to lower the MTU size.

However, the script under /etc/network/if-up.d is not automatically triggered.

Does something change with the newer Ubuntu version?

Francesco Taioli
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1 Answers1

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I managed to workaround it with NetworkManager-dispatcher. The doc can be found on arch.

The scripts must be moved from /etc/network/if-{up,down}.d/ to /etc/NetworkManager/dispatcher.d/. You can use the second argument $2 to branch on the specific event (up, down...).

Also, the usage of IFACE env var must be replaced with either VPN_IP_IFACE, DEVICE_IP_IFACE, or DEVICE_IFACE as applicable.

Note: Although networkd-dispatcher is a recommended modern way to trigger scripts, those were not executed on my Ubuntu 24.04 (desktop).

Eric M.
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