[Lxc-users] seeing a network pause when starting and stopping LXCs - how do I stop this?

[Michael H. Warfield]

On Thu, 2011-12-08 at 19:47 +1300, Gary Ballantyne wrote: 
> On 08/12/11 19:39, Daniel Lezcano wrote:
> > On 12/08/2011 12:38 AM, Joseph Heck wrote:
> >> I've been seeing a pause in the whole networking stack when starting
> >> and stopping LXC - it seems to be somewhat intermittent, but happens
> >> reasonably consistently the first time I start up the LXC.
> >>
> >> I'm using ubuntu 11.10, which is using LXC 0.7.5
> >>
> >> I'm starting the container with lxc-start -d -n $CONTAINERNAME
> > That could be the bridge configuration. Did you do 'brctl setfd br0 0' ?

> FWIW, I see the same issue following [1], which has 'brctl setfd br0 0'.

> [1] 
> http://www.activestate.com/blog/2011/10/virtualization-ec2-cloud-using-lxc

That just sets the "bridge delay" to zero (which could have an impact)
but does not change the MAC address policy of assigning the "lowest" MAC
address to the bridge itself.

If the bridge mac address changes then any OTHER nodes or routers on the
network have to fail out their ARP caches and re-ARP for the new MAC
address, resulting in the delay.  The only way to work around this
problem is to assign very high MAC addresses to the nodes on the bridge
to keep them from changing the MAC address of the bridge itself.
Setting the "locally administered" (0200 in first word) bit in the MAC
address helps but may not be sufficient (warning - DO NOT set the
MULTICAST bit (0100 in first word)!).

This was a design decision made many years ago in the Linux kernel for
reasons I did not agree with and do not agree with but it is what it is
and I doubt it will ever change.  I think there's a patch going into the
lxc-tools to avoid this problem.

Regards,
Mike

-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
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