mtu on Linux vs MacOS

[Roman Mamedov]

On Thu, 21 Jan 2021 19:07:18 +0500
Roman Mamedov <rm at romanrm.net> wrote:

> On Sun, 17 Jan 2021 11:36:42 +0100
> Harald Dunkel <harri at afaics.de> wrote:
> 
> > Hi folks,
> > 
> > I am using PPPoE to connect to my IP provider. To use wireguard on Linux I
> > have to reduce the MTU in wg0.conf to 1400. Using the default 1420 a ssh
> > connection tunneled through wireguard gets stuck (reproducible). An echo
> > of a very long line (e.g. 4096 chars) is sufficient.
> > 
> > The weird part is, MTU 1420 works fine for wireguard on MacOS. How comes
> > that Wireguard appears to be more stable on MacOS than on Linux?
> 
> WireGuard works just fine for me on Linux using MTU 1432 if over IPv4, and
> 1412 if over IPv6. The underlying PPPoE device MTU is 1492 in my case. Check
> which PPPoE MTU you use in Linux vs in MacOS.
> 

Oh, and I just remembered -- you're better off setting the same MTU on the
entire WG network, i.e. substract those 8 bytes of PPPoE interface on the
remote host's WG interface as well. Else the local interface MTU will need a
weird and so far unexplained further 4-byte reduction for things to work:
https://lists.zx2c4.com/pipermail/wireguard/2019-April/004078.html

-- 
With respect,
Roman