MTU on wireguard-apple for IPv6

[Jason A. Donenfeld]

On Thu, Dec 19, 2019 at 2:21 AM Rémi Lapeyre <remi.lapeyre at henki.fr> wrote:
> Does `networkSettings.tunnelOverheadBytes = 80` means the MTU will
> used be the one of the interface minus 80 bits of overhead for the
> WireGuard protocol?

Right, it means the MTU of the WireGuard interface will be the MTU of
your wifi interface minus 80.

> Some of our users where tethering over their phone connection so it
> seems that 1280 is appropriate in that case, but I’m confused as to
> why connections not going through the WireGuard tunnel where not
> impacted in that case.

Probably the phone's dhcp server doesn't pass the right MTU back to
the client, but then the phone does the mss-mtu hack to fix up TCP
connections. That hack doesn't work when the traffic is end-to-end
encrypted, as is the case with WireGuard, so no smaller MSS is ever
negotiated.