Settings for OpenWrt as DHCP client

Installing and Using OpenWrt
1

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

network.eth0.proto='dhcp'

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?

2

LuCI > Network > Interfaces > Devices tab.

3

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

4

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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5

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/dhcp.sh

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6

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