[ovirt-users] selectively disabling IPv6 on bridges

Dan Kenigsberg danken at redhat.com
Thu May 7 10:46:05 UTC 2015

On Wed, May 06, 2015 at 01:53:35PM +0100, Dan Kenigsberg wrote:
> On Wed, May 06, 2015 at 01:28:30PM +0200, Rik Theys wrote:
> > Hi,
> > 
> > I'm looking for a way to selectively disable IPv6 on the bridge interfaces
> > on the oVirt hosts.
> > 
> > When oVirt creates the bridges for all logical networks on the host, it
> > keeps the default settings for IPv6 which means all bridges get a link-local
> > address and accept router advertisements.
> > 
> > When a VM is created on the logical network, it can now reach the host over
> > IPv6 (but not over IPv4 if no IP address has been assigned on the host). If
> > it sends out a router advertisement it can even create a global IPv6 address
> > (haven't tested this).
> > 
> > How can I prevent this?
> > 
> > I would like to prevent the guest from IPv6 access to the host but the guest
> > itself still needs IPv6 access (global IPv6 addresses).
> > 
> > Is it sufficient to create a sysctl config file that says:
> > 
> > net.ipv6.conf.default.disable_ipv6 = 1
> Yes, I believe that this would do the trick. For any newly-created
> device on the system, regardless of ovirt bridges.
> I now see that el7 has changed the default for IPV6INIT to "yes". We
> should be more prudent and set IPV6INIT=no on all our devices.

Lukáš, it seems that setting IPV6INIT=no is not enough:

      Enable or disable IPv6 static, DHCP, or autoconf configuration for this interface
      Default: yes

The bridge still gets a link-local ipv6 address anyway. Is there an initscript
means to disable this completely, or should we resort to
/proc/sys/net/ipv6/conf/<bridge-name>/disable_ipv6 ?


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