MTU for Devices wan and pppoe-wan

Hey all!

Quick question regarding MTU: I am dialing in via PPPoE on the router, so I have two WAN-related devices, wan (switch port) and pppoe-wan (tunnel interface). Which MTU value should I set on each? Let's say my DSL connection has a max MTU of 1472, do I set it on both wan and pppoe-wan, or only on wan, and 1500 on pppoe-wan? And why?

Thanks! :slight_smile:

Ideally on Openwrt you do not need to do anything as the defaults tend to be quite OK.

BUT if you have something like eth0(wan) with pppoe-wan on top, that eth0's MTU needs to be at least 8 byte larger than pppoe-wan's after all that 8 byte PPPoE overhead needs to be transported to the ISP...

1472 seems unusual, typically we see 1492, as together with the 8 byte overhead that adds up to the 1500 bytes a typical ethernet link will carry...

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And then there is this:

https://homenetworkgeek.com/mtu-size/
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