Re: [Xen-devel] ipv6 addresses on vifX.Y interfaces and bridges

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

On Mon, Jan 07, 2008 at 09:44:09AM +1100, James Harper wrote:
> > On Mon, Jan 07, 2008 at 09:26:43AM +1100, James Harper wrote:
> > > The network scripts appear to set noarp on all the vifX.Y and
> xen-brX
> > > interfaces, but I also need to remove the IPv6 address and stop the
> > > interfaces participating in autoconfiguration...
> > >
> > > Has anyone done this already?
> > 
> > You don't need to remove the link-local IPv6 addresses, they are
> harmless.
> > The key is to stop auto-conf taking place on the bridge. The way todo
> > this is to set the mtu of the bridge to something tiny (eg 68) before
> > bringing the interface up, and then once it is up, restore the mtu to
> > its normal 1500.
> > 
> > This was previously merged in xen-unstable, in 13364
> 
> That sounds a bit kludgy... wouldn't it be better to make use of
> /proc/sys/net/ipv6/<interface>/autoconf and/or .../accept_ra?

Would have to ask Herbert about that - when he wrote the patch this was
the only reliable way of selectively disabling Ipv6 on the bridge, but
not other eth devices.

> Wouldn't the bridge just autoconf next time an ra is sent once its mtu
> is back up to 1500?

No, because the low MTU means it never gets assigned a link-local address
and thus has no way to parcitipate in ipv6 autoconf thereafter.

Dan.
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