[Bug 220351] Path MTU discovery works only after resetting an internal interface MTU (mpd5, ng_nat, ipfw)

[Herbert J. Skuhra]

bugzilla-noreply skrev:
> 
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=220351
> Eugene Grosbein <eugen at freebsd.org> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>            Assignee|freebsd-net at FreeBSD.org     |eugen at freebsd.org
>              Status|New                         |Open
>                  CC|                            |eugen at freebsd.org
> 
> --- Comment #2 from Eugene Grosbein <eugen at freebsd.org> ---
> (In reply to Martin Birgmeier from comment #1)
> 
> Lowering interface MTU of internal machine also lowers its default route 'mtu'
> attribute, see output of the command 'route -n get default'.
> 
> Raising interface MTU back does NOT restore 'mtu' attribute of the default
> route, so the kernel still uses 1492 as maximum IP packet size for packets
> going via this route.
> 
> Correct solution for your problem is 'set iface enable tcpmssfix' command in
> the mpd.conf, see /usr/local/etc/mpd5/mpd.conf.sample for example. This way you
> can keep default MTU=1500 for internal hosts and have no MTU-related network
> problems.
> 
> Please test and report back.

I think I have a similar problem, but with IPv6 and pf! :-(

- Problem to load e.g. https://www.heise.de on the first try
- Can not connect to Skype for Business over IPv6 (unfortunately I
sometimes need it for job)

Everything else is obviously working.

Does anyone know how to fix this?

Thanks.

--
Herbert