Hi Lukasz, Carrier network providers use bearer information to carry the MTU setting, this can be received by the modem then exposed to its host system either via NetworkManager's ipv4_config or ipv6_config.
I think ipv4_config is the must supported setting in carrier's network, that may be why this upstream patch has not considered ipv6_config. (MTU should be the same(per device) for both ipv4 and ipv6) Our customer has used this patch in the field testing and this patch worked as expected. There should be no concern to get MTU only via ipv4_config. Thanks for highlight this question. -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to network-manager in Ubuntu. https://bugs.launchpad.net/bugs/1955797 Title: [SRU] network-manager can’t modify MTU automatically based on what ModemManager exposes for WWAN modems. Status in network-manager package in Ubuntu: Fix Released Status in network-manager source package in Focal: New Bug description: [Impact] Some 4G/5G mobile networks(for ex., AT&T) requires a specific MTU setting, this setting will be exposed by the ModemManager for network- manger to configure the MTU of the modem network interface . The current modem-manager v1.22.10-1ubuntu2.2 in focal can’t pass AT&T’s modem system certification. [Fix] This upstream patch can resolve this bug: https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/499/diffs?commit_id=212758ea05a4c13d65f36b55c90aee7919642631 [Test Plan] 1. Use a Lenovo platform SE30 including 4G Quectel EM160 modem and an AT&T SIM card in US 2. Enable 4G modem and connect to AT&T apn $ sudo mmcli -i 0 --pin=0000 $ sudo mmcli --modem 0 --enable $ sudo mmcli -m 0 --simple-connect="pin=0000,apn=emome" $ sudo nmcli radio wwan on $ sudo nmcli connection add type gsm ifname wwan0p2MBIM con-name mymodem apn emome $ sudo nmcli connection up id mymodem 3. Check if the MTU got from the following results are the same: $ sudo mmcli --bearer 5 | mtu $ ifconfig mhi_mbim0 | grep mtu * Expected result: Both MTUs are the same value 1430 * Actual tested result: Different values (one is 1430 , another is 1500) [Where problems could occur] Very low. This is a simple fix: network-manager gets the MTU from the ModemManager then sets the MTU of the modem interface. [Other info] 1. Network-manager v1.30.0-1ubuntu3 in hirsute has included the fix. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1955797/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp
