Comment # 2 on bug 1113199 from James Fehlig

(In reply to William Brown from comment #0)
> When creating a virtual network in libvirt, even with ipv6 enabled = true in
> virt-manager, or a configuration such as:
> 
> <network ipv6='yes'>
>   <name>ra2</name>
>   <uuid>98e7a9a1-9606-4bf0-b9ed-13bda85e7ee2</uuid>
>   <bridge name='virbr2' stp='on' delay='0'/>
>   <mac address='52:54:00:72:83:79'/>
>   <domain name='ra2'/>
> </network>
> 
> Ipv6 traffic does not function correctly on the created bridge device. The
> cause is that the sysctl for the associated bridge is not correctly
> configured:
> 
> # sysctl -a | grep -i disable_ipv6
> ...
> 
> net.ipv6.conf.virbr2.disable_ipv6 = 1
> net.ipv6.conf.virbr2-nic.disable_ipv6 = 0

Looking at the network driver code, disable_ipv6 is set if there are no ipv6
addresses defined for the network

https://libvirt.org/git/?p=libvirt.git;a=blob;f=src/network/bridge_driver.c;h=4bbc4f5a6d494dec8249c7bd0d4dbc1baefcf9bd;hb=HEAD#l2226

Does it work if you assign and address to the network? E.g.

<network ipv6='yes'>
  <name>ra2</name>
  <uuid>98e7a9a1-9606-4bf0-b9ed-13bda85e7ee2</uuid>
  <bridge name='virbr2' stp='on' delay='0'/>
  <mac address='52:54:00:72:83:79'/>
  <ip family="ipv6" address="2001:db8:ca2:6::1" prefix="64"/>
  <domain name='ra2'/>
</network>

I suppose you've already looked at the example in the docs

https://libvirt.org/formatnetwork.html#examplesPrivate6

That said, I wonder if the code needs to be updated to set disable_ipv6=0 when
ipv6='yes' is set on the <network> element...