[libvirt] IPV6 and routing

Gene Czarcinski gene at czarc.net
Mon Oct 8 13:31:59 UTC 2012


On 10/07/2012 12:10 PM, Gene Czarcinski wrote:
> 1. Manually configure the IPv6 address/network on the virtualization 
> host.  On the default route system, add a static route to the 
> virtualization host.  Things will then work.
>
> 2.  It hurts, don't do it: use a bridge in the virtualization host for 
> IPv6 virtual networks which need to access external systems.
>
> BTW, this is also needed for support of IPv4 routed networks. This can 
> be made a little easier by using 172.16.<nn>.0/24 networks and adding 
> a single static route for 172.16.0.0/16. 
Giving this some additional thought, there is a small alternative which 
offers some advantages: use dhcp "nailed" host ip addresses. while this 
works for both IPv4 and IPv6, it is more important for IPv6 because all 
IPv6 virtual networksare "routed."

I have tested this using dnsmasq as the dhcpd6 and dns services provider 
and there are a number of options for relating a specific 
host/network-interface and an ip address.  In addition to dnsmasq or 
dhcpd6, you will need to add a static route for that virtual network to 
the virtualization  host on the system which is pointed to by the 
default route.

There are some documents out there which imply to what I have concluded 
above but things are left still a little vague.  Examples of what is out 
there are:

http://berrange.com/posts/2009/12/13/routed-subnets-without-nat-for-libvirt-managed-virtual-machines-in-fedora/

http://blog.gadi.cc/routed-subnet-libvirt-kvm/

But, I do not see (or have not found yet) something under 
http://wiki.libvirt.org

I am not sure where such information belongs but I do believe that it is 
needed.  Examples of where it could be placed are:

http://wiki.libvirt.org/page/VirtualNetworking#Routed_mode_2

http://wiki.libvirt.org/page/Networking

http://libvirt.org/formatnetwork.html#examplesRoute

Gene




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