IPv6 neighbor discovery not getting through qbr bridge

[David Reno]

Summary:
========
Newton nova on CentOS 7.3 is setting the qbr bridge to disable IPv6 (virt/libvirt/vif.py:536)

This is preventing IPv6 neighbor discovery from getting through the bridge and thus all IPv6 connectivity.

Details:
========
Version: Newton on CentOS 7.3 minimal (CentOS-7-x86_64-Minimal-1611.iso) as per these instructions: http://docs.openstack.org/newton/install-guide-rdo/

Seemingly relevant sections of nova-compute.log:
ova-compute.log:2017-02-09 10:41:55.878 8393 DEBUG oslo_service.service [req-06596ba4-20c6-40bc-b6a0-37f84aaa2e49 - - - - -] os_vif_linux_bridge.use_ipv6 = True log_opt_values /usr/lib/python2.7/site-packages/oslo_config/cfg.py:2630
nova-compute.log:2017-02-09 11:04:12.281 8393 DEBUG oslo.privsep.daemon [-] Running cmd (subprocess): tee /proc/sys/net/ipv6/conf/qbr91c6f3e4-bd/disable_ipv6 out_of_band /usr/lib/python2.7/site-packages/oslo_privsep/daemon.py:194

[David Reno (dcreno)]

So this is on purpose apparently (not sure why the config option exists): https://github.com/openstack/nova/commit/5ab1b1b1c456b8b43edbd1bddd74b96b56ab80e6

The question remains why IPv6 neighbor discovery won't go though until I enable IPv6 on the bridge via sysctl.

[Sylvain Bauza (sylvain-bauza)]

All the discussion can be found in https://bugs.launchpad.net/neutron/+bug/1302080

Basically, it was possible to reach from a guest perspective the hypervisor in case the bridge was also IPv6. The solution was rather to stop using IPv6 for that bridge automatically.

That doesn't mean that you can't use IPv6 IMHO, just that the bridge won't use it automatically.

Anyway, the above bug report I provided to you seems the best for discussing about your problem, I'd like to put this one as Opinion as I'm not sure Nova can help here.