Hey all,

According to a discussion last week in the Nova-Libvirt subgroup meeting, it 
was advised, by danpb, that I bring this issue up on the Libvirt mailing list 
for discussion and resolution. So, here goes -

I'm currently using config drive from Nova to generate network configurations 
for LXC guests that are spun up via Libvirt. Unfortunately, when doing some 
IPv6 testing, I ran into a snag (with a couple work arounds detailed below). 
Due to the read-only mount of /proc/sys 
(http://libvirt.org/drvlxc.html#fsmounts), I am unable to get expected behavior 
from IPv6 static network configurations. I did some poking around and found 
this bug from a couple years ago that pretty well outlines the problem: 
https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/964882.

I wasn't sure how we might go about correcting this, but it seems like 
something we'll need to address in Libvirt. Maybe with the user namespaces 
working, we can begin to provide some read/write mounts instead of read-only 
with clear documentation on the security implications? =] When using static 
IPv6 addressing it was attempting the following command: 'sysctl -q -e -w 
net.ipv6.conf.eth0.autoconf=0'. I tested to see whether the host and the guest 
share this value. I was able to change it in the host without it being 
reflected in the guest.

The work arounds I've tried that seemed to allow IPv6 to get configured 
properly:

1. Use the post-up hook on an IPv4 static configuration to configure IPv6 via 
ifconfig/routes (example: http://paste.openstack.org/show/82446/).
2. Patch Libvirt to include a /proc/sys/net mount as read/write.

Cheers!

-Thomas

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