MTU of mobile interface RUTX50 07.04.4


According to both ip -4 link and ip -6 link, the qmimux0 interface has a MTU of 1500 bytes.
There is no “option mtu ‘xxxx’” in the mob1s1a1 section of /etc/config/network.
The router uses bands B3 + 5G N28 NSA, the modem reports:

root@lgr5g:~# gsmctl -A 'AT+QMTUINFO'
+QMTUINFO: 1,1416,1416
+QMTUINFO: 2,1500,1280

So the MTU of qmimux0 should be set to 1416 bytes if it uses IPv4 only and 1280 bytes if it uses both IPv4 and IPv6.
Of course the MTU of wireguard and openvpn / IPSEC interfaces have to be restricted accordingly.

May I have missed something ? Could this be the root cause of the netifd’s coredumps ?



I have the same problem with rutX11 and rut240 since v7.4.

I opened a ticket in their helpdesk system and this is what they answered:

After consulting with our R&D department, they have confirmed that they are planning to improve this change with later Firmware releases, so the MTU advertised in the network would be used by default. It is currently unknown when this change will be introduced, however, as of now, it is expected to be implemented with the RUTOS 7.6 Firmware release.


Thank you. I have set up a workaround using /etc/mwan3.user

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