On a CentOS 6.5 host, I have a couple of guests - Ubuntu 12.04 and CentOS 6.5. The Ubuntu guest is generating mcast traffic that is visible via a tcpdump on the br3 interface. It is also visible on the other VM.

It is not on the associated eth3 interface, nor does it make it out the wire to other hosts.

We've been through bridged networking with kvm and this:

$ sed -I 's/^\(net.ipv4.ip_forward =\).*/\1 1/' /etc/sysctl.conf; sysctl -p 

Along with these articles titled:

Does anyone have anything else?

1 Answer 1


We do not understand what was under SELinux control, but something was and simply turning off selinux and rebooting got it working.

SELinux: Secure or Useable. Pick one.

  • 1
    Did you try running with "Permissive' settings, and simply following the popups to enable whatever selinux was complaining about?
    – Dani_l
    Commented Nov 22, 2016 at 14:35

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