> In my case, the PPPoE interface got MTU=1480. They might be stacking > something else on top of it or PPPoE might have optional fields. I > read somewhere that PPPoE might use either 8 or 20 bytes, but I'm not > an expert on PPPoE.
For ref, an L2TP + PPPoE stack isn't too uncommon, and gives you 20 bytes overhead from the 12 bytes L2TP + 8 bytes PPPoE. On Wed, Aug 23, 2023 at 12:02 PM Luiz Angelo Daros de Luca <luizl...@gmail.com> wrote: > > > Hi, > > Hi Daniel, > > > On Wed, Aug 23, 2023 at 04:58:40PM +0200, Marek Küthe wrote: > > > PPPoE adds 8 bytes of overhead so that an MTU of 1432 can be used. I > > > also have to do this at home with my DSL line for example. > > > The MTU should be set on each side (on both peers) for this to work. > > > > Oh, I just realized I used the 1432 MTU in my earlier reply based on > > Marek's math but since Luiz's underlay network is IPv6 this is not actually > > correct. MTU=1440 is only correct on top of IPv4, for IPv6 the "optimal" > > MTU is 1420 so with PPPoE involved that's MTU=1412. > > > > 1500 Ethernet payload > > -40 IPv6 header > > -8 UDP header > > -32 Wg header > > -8 PPPoE > > =================== > > 1412 wg tunnel MTU > > In my case, the PPPoE interface got MTU=1480. They might be stacking > something else on top of it or PPPoE might have optional fields. I > read somewhere that PPPoE might use either 8 or 20 bytes, but I'm not > an expert on PPPoE. If I don't control both sides, I would use 1400 by > default. > > > --Daniel