libvirt users - Sep 2019 - Re: Privacy Extension not working in VM

Hello @ all

With the rebuilding of my Server from Debian 9 to Debian 10, I also 
switch from Virtual Box to Libvirt/KVM. Due to new requirements for the 
VMs, now I have an actual problem, which unfortunately I can not solve. 
The problem has already been discussed in the German Debian-Forum ... 
unfortunately also without success.

The facts:
- ISP = Dual Stack with daily separation
- Host and VM = Debian 10
- The VMs are via macvtap-device regular LAN-Clients
   - IPv4 = DHCP and NAT by DSL-Router
   - IPv6 = GUA via RA and SLAAC (2003::/3)
- IPv4 works fine in the VM
- IPv6 (NDP, RA, SLAAC) works basically also fine in the VM

The existing problem in the VM:
- MAC-Based GUA (2000::/3) is ok, both inbound and outbound

- Outbound traffic via the second GUA (PE-Based) is filtered apparently,
   but not via packetfiltering, I don't know where. There are no error
   messages. On the part of the kernel in the VM and the IPv6-stack,
   everything looks completely ok, no error messages, except that
   Outbound-Traffic by the PE-Address is quietly blocked. The MAC-
   Based IPv6 works unchanged and without error as before.

My questions:
1. Is there a special setting for the VM, to allow the use of Privacy
    Extensions for IPv6 unlimited?
2. Or is that possibly even a known and at the moment unsolved problem?
3. Or is this a intended limitation of virtualization?

Can anyone help me with a solution or a hint? Thank you.

BR, Tom

On Sat, Sep 21, 2019 at 11:28:56AM +0200, Thomas Luening
wrote:
> Hello @ all
> 
> With the rebuilding of my Server from Debian 9 to Debian 10, I also switch
> from Virtual Box to Libvirt/KVM. Due to new requirements for the VMs, now I
> have an actual problem, which unfortunately I can not solve. The problem
has
> already been discussed in the German Debian-Forum ... unfortunately also
> without success.
> 
> The facts:
> - ISP = Dual Stack with daily separation
> - Host and VM = Debian 10
> - The VMs are via macvtap-device regular LAN-Clients
>   - IPv4 = DHCP and NAT by DSL-Router
>   - IPv6 = GUA via RA and SLAAC (2003::/3)
> - IPv4 works fine in the VM
> - IPv6 (NDP, RA, SLAAC) works basically also fine in the VM
> 
> The existing problem in the VM:
> - MAC-Based GUA (2000::/3) is ok, both inbound and outbound
> 
> - Outbound traffic via the second GUA (PE-Based) is filtered apparently,
>   but not via packetfiltering, I don't know where. There are no error
>   messages. On the part of the kernel in the VM and the IPv6-stack,
>   everything looks completely ok, no error messages, except that
>   Outbound-Traffic by the PE-Address is quietly blocked. The MAC-
>   Based IPv6 works unchanged and without error as before.
> 
> My questions:
> 1. Is there a special setting for the VM, to allow the use of Privacy
>    Extensions for IPv6 unlimited?
> 2. Or is that possibly even a known and at the moment unsolved problem?
> 3. Or is this a intended limitation of virtualization?
> 
> Can anyone help me with a solution or a hint? Thank you.
You mention you used 'macvtap' but not which mode of macvtap ? None the
less if you're using it in bridge mode, or passthroug hmode, there should
be no filtering of guest traffic in general, since the guest traffic is
forwarding at the ethernet layer, not IP layer.

The exception would be if you hve the br-netfilter extension loaded which
causes guest traffic to be processed by the host firewall.

Regards,
Daniel
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Hi Daniel,

thanks for your response.
> You mention you used 'macvtap' but not which mode of macvtap ? None
the
> less if you're using it in bridge mode, or passthroug hmode, there
should
> be no filtering of guest traffic in general, since the guest traffic is
> forwarding at the ethernet layer, not IP layer.
> 
> The exception would be if you hve the br-netfilter extension loaded which
> causes guest traffic to be processed by the host firewall.
The macvtap-Device is started in bridge mode via a systemd-service-unit 
before the VM is started, see below. The kernel module br-netfilter for 
Packetfiltering is not loaded.  But the PE-based IPv6 is still blocked 
furthermore. The MAC-based IPv6 works fine.

BR, Tom

# cat /etc/systemd/system/kvm-network-lan.service
[Unit]
Description=kvm-local-network.service     Setup a macvtap-Bridge for 
Client-Integration in LAN
After=network.target
Wants=network.target

[Service]
Type=oneshot
RemainAfterExit=yes

ExecStartPre=/usr/sbin/ip link add link enp2s0 macvtap0 address 
d0:50:99:0a:0a:0a type macvtap mode bridge
ExecStartPre=/usr/sbin/ip link set macvtap0 up
ExecStart=/usr/sbin/ip link show macvtap0

ExecStop=/usr/sbin/ip link set macvtap0 down
ExecStopPost=/usr/sbin/ip link del macvtap0

[Install]
WantedBy=multi-user.target


# cat /etc/libvirt/qemu/vm1.xml | grep "<interface" -A 5
     <interface type='direct'>
       <mac address='d0:50:99:0b:0b:0b'/>
       <source dev='macvtap0' mode='bridge'/>
       <model type='virtio'/>
       <address type='pci' domain='0x0000' bus='0x01'
slot='0x00'
function='0x0'/>
     </interface>