Just a small update on things. Maybe someone finds it useful. I did a little bit of digging into wan packet overhead and really read the cake documentation.
The number should be 34 for most FTTC connections. Reason being is that yes vdsl2 pppoe is 30 but if the ISP uses vlan tagging (e.g. BT) then you must also consider the ether-vlan tag which adds 4 bytes.
The PTM flag should also not be set (noatm). It’s better to just present cake with a slightly modified download bandwidth to account for the 64/65 octet encapsulation of ptm (0.984 of your bandwidth). This should in theory lead to less CPU strain since cake doesn’t have to adjust the accounted packet size.
I’m currently looking into MPU. From here: https://openwrt.org/docs/guide-user/network/traffic-shaping/sqm-details#more_hints_tips_info
Something around 72 perhaps. Not sure of the relation between bridged-ptm and pppoe vdsl based on his info but if bridged-ptm = 22 then it makes sense that you would add 8 from the pppoe vdsl mpu (both have ether-vlan) so thus mpu should be 80. I’ll look around a little more and see if I can get any extra info.
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