Cloud instance with reduced MTU, container uses 1500, connections stall

Serge Hallyn serge.hallyn at
Mon Jun 16 18:12:09 UTC 2014

Quoting Andreas Hasenack (andreas at
> On Mon, Jun 16, 2014 at 2:11 PM, Serge Hallyn <serge.hallyn at>
> wrote:
> >
> > Right, the problem is that if lxc was going to try to autoset the veth
> > mtu then it should set it to equal the mtu of its bridge, lxcbr0.  So
> > if we don't set lxcbr0 to match the host NIC then there's nothing lxc
> > could realistically do anyway.
> >
> > Anyway this still seems ok to me - if we update /etc/init/lxc-net.conf
> > to have lxcbr0 mtu match the host nic's mtu, and then have lxc drop
> > the veth mtu (if not specified in configuration file) to match
> > the veth link's (lxcbr0, br0, whatever is specified in the config).
> >
> > I'm open to other suggestions.
> >
> >
> >
> How do we know which interface to match the lxcbr0 MTU with? In this case
> it was eth0, but it could be anything, right?

Correct.  We can make some guesses based on default route, but I'm not
sure how comfortable I am doing that.

More information about the ubuntu-server mailing list