I discovered the instances in my home lab were not being protected by the neutron security groups I’d set up for them – what followed was a week-long odyssey to discover the culprit. IPTables rules were being put in place, and every other aspect of Neutron networking was just fine. Making things more mysterious, a test deploy on my own desktop, with the host running Fedora 23 and the containers running CentOS 7, did not manifest the issue.

Security groups are applied to the tap interface closest to the virtual machine, shown above (not mine – click the image to see the rest of that excellent tutorial).

It turns out there’s a pair of kernel tunables that govern whether or not iptables rules are applied to  interfaces that are members of a bridge, as in this instance. It also turns out that Red Hat, for some reason, toggled the default value of this tunable to 0 after RHEL 7 was released.

These tunables, and their required values, are:

net.bridge.bridge-nf-call-iptables = 1
net.bridge.bridge-nf-call-ip6tables = 1

And this needs to be set on the outer host, if you run your OpenStack cloud in containers. If not and/or otherwise, you need this set on your compute nodes as this is where security groups are set.

Hope this saves someone a week of troubleshooting! 🙂