Settings for OpenWrt as DHCP client

I have an OpenWrt device configured as a DHCP client on my network. I did this with the usual UCI option, ie:


This works for IP autoconfiguration, but the MTU remains the default 1500 instead of picking up the 1400 MTU that is served via DHCP option 26 on my network. I have multiple Ubuntu clients on my network that successfully pick up the 1400, so I know it's working at the DHCP server end.

Presumably the DHCP client in OpenWrt is simply configured by default not to accept MTU via option 26, but I'm drawing a blank trying to find any way to set DHCP client configuration options beyond the above. Can anyone point me in the right direction?

LuCI > Network > Interfaces > Devices tab.

Thanks, but that only enables manual changing of interface MTU. My question was how to configure the DHCP client to obtain MTU automatically.

DHCP doesn’t agree and set MTU values as far as I am aware. DHCP only agrees on a IP address.
1500 is pretty much regarded a preset industry and world standard so why do you have 1400?

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DHCP clients must request for the various options for the server to return them.
OpenWrt requests for 121, classless static routes.
ps wwww | grep udhcp

Check line 43 at /lib/netifd/proto/


Well I guess I must have been hallucinating the fact that I've been using it successfully to do exactly that for years.