Set MTU parameter

I have an OpenWRT router behind ADSL modem-router.
ADSL MTU is set to 1492.

should I set MTU for WAN and other interfaces on OpenWRT to same value?


As far as I understand, MTU value needs to be entered once, in the device that terminates the PPPoE.

Therefore, if you have an xDSL modem or an xDSL modem m-outer in bridge mode, you would have ISP MTU value entered in the next router (well, actually it is the first router since the modem isn't doing any routing), which will have its WAN connection as PPPoE.

If on the other hand your modem-router is doing routing, then yout don't need to worry about MTU for downstream routers.

Edit: to clarify, I don't think it harms to enter it in all routers, but if you have it only in the first router, I think the other routers well figure out the least value you have entered and will use it.

1 Like

AAs long as MSS Clamping is set on your WAN you do not need to worry about specifying MTU on any other interface except the WAN.

1 Like