Libvirt IPv6 routing to nated network

Andrew

1/7/24, 9:15 PM

I'm having trouble getting IPv6 to work for my KVM/qemu guests.

I have two bridges setup, one routed (external, non libvirt) bridge for public dedicated ipv4 + ipv6 which works for both protocols.

Then I have a libvirt nat bridge (with the routed bridge as parent) with a nated ipv4 (that works) and I also want a public ipv6. I'm able to transmit udp packets out but I never get any response.

Looking at tcpdump there are incoming neighbor solicitations that get unanswered and don't get forwarded to the guest.

Do I need to set something special up for this to work? Ubuntu 22.04 / Libvirt 8.0.0

The routed bridge (pubBr) has ipv6 2001:x:x:7d8e:: - My nat bridge xml config below:

<network>
    <name>natbr</name>
    <bridge name="natbr" />
    <forward mode='nat' dev='pubBr'>
      <nat>
        <port start='8000' end='30000'/>
      </nat>
    </forward>
    <ip address="10.1.1.1" netmask="255.255.0.0">
      <dhcp>
        <range start='10.1.1.2' end='10.1.1.255'/>
      </dhcp>
    </ip>
    <ip family="ipv6" address="2001:x:x:7d8e::1" prefix="64">
      <dhcp>
        <host name="test" ip="2001:x:x:7d8e:a01:2ff::"/>
      </dhcp>
    </ip>
  </network>

192

0 + 1

ipv6

libvirt

qemu

kvm-virtualization

Ron Maupin

1/16/24, 1:29 AM

Bridges do not route. Bridges (switches are bridges) bridge layer-2 frames on the same network. but routers route layer-3 packets between networks. Bridges know nothing , nor do they care, about layer-3 (IP) packet addresses, only switching frames based on the layer-2 frame addresses. NAT translates layer-3 IPv4 packet addresses, so switches know nothing about NAT. IPv6 does not have a NAT standard the way IPv4 does, not needing NAT that is a kludge to extend the life of IPv4 until IPv6 can become ubiquitous.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Libvirt IPv6 routing to nated network

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