[OpenWrt-Devel] netifd: per-interface MTU settings vs per-route MTU settings?

[Aleksander Morgado]

Hey,

> >> There's an ongoing discussion in the ModemManager package in github
> >> related to how the MTU may be configured in the network interface
> >> based on what the MM bearer object reports:
> >> https://github.com/openwrt/packages/issues/11383
> >>
> >> E.g.:
> >>
> >> $ ip route show
> >> default via 25.225.105.222 dev wwan0 proto static src 25.225.105.221 mtu 1430
> >>
> >> Looks like the protocol handler implementation for netifd may allow
> >> setting the MTU to the routes associated with the network interface,
> >> instead of assigning the MTU value to the interface itself. Are both
> >> methods completely equivalent? Is there any reason to avoid setting
> >> the MTU in the interface when using netifd, or just not implemented
> >> yet?
> >>
> >> Cheers!
> >>
> >> --
> >> Aleksander
> >> https://aleksander.es
> >
> >
> >
> >
> > I'm actually not aware of any method to set the interface MTU via netifd that isn't a UCI setting.
> >
>
> While running as a protocol handler under netifd, we can do this while
> setting up the default route:
>   proto_add_ipv4_route "0.0.0.0" "0" "${gateway}" "${address}"
> "${metric}" "${mtu}"
> And the given ${mtu} will be set for the route created.
>
> What we're looking for is a way to setup the MTU for the whole network
> interface from within the protocol handler automatically.
>

Other protocol handlers, like uqmi, are also able to setup the MTU,
and instead of doing it via proto_send_update, they just do it like
this:

        [ -n "$mtu" ] && {
                echo "Setting MTU to $mtu"
                /sbin/ip link set dev $ifname mtu $mtu
        }

I guess we can do the same in the ModemManager protocol handler.

-- 
Aleksander
https://aleksander.es

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