[libvirt-users] What's the best way to make use of VLAN interfaces with VMs?

[Richard Achmatowicz]

Hello

I have a problem with attaching VMs to a VLAN interface.

Here is my setup: I have several physical hosts connected by a physical 
switch.  Each host has two NICs leading to the switch, which have been 
combined into a team, team0. Each host a has a bridge br1, which has 
team0 as a slave. So communication between hosts is based on the IP 
address of bridge br1 on each host.

Up until recently, using libvirt and KVM, I was creating VMs which had 
one interface attached the default virtual network and one interface 
attached to the bridge:

virt-install ... --network network=default --network bridge=br1 ...

I would then statically assign an IP address to the bridge interface on 
the guest when installing the OS.

A few days ago, a VLAN was introduced to split up the network. I created 
a new VLAN interface br1.600 on each of the hosts. My initial attempt 
was to do try this:

virt-install ... --network network=default --network bridge=br1.600 ...

which did not work. It then dawned on me that a VLAN interface and a 
bridge aren't treated the same. So I started to look for ways to allow 
my VMs to bind to this new interface.

This would seem to be a common situation. What is the best way to work 
around this?

Both the host bridge and the host VLAN interface already have their 
assigned IP addresses and appear like this in libvirt:

[root at clusterdev01 ]# ifconfig
br1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
         inet 192.168.0.110  netmask 255.255.255.0  broadcast 192.168.0.255
         inet6 fe80::1e98:ecff:fe1b:276d  prefixlen 64  scopeid 0x20<link>
         ether 1c:98:ec:1b:27:6d  txqueuelen 1000  (Ethernet)
         RX packets 833772  bytes 2976958254 (2.7 GiB)
         RX errors 0  dropped 0  overruns 0  frame 0
         TX packets 331237  bytes 23335124 (22.2 MiB)
         TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

br1.600: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
         inet 192.168.1.110  netmask 255.255.255.0  broadcast 192.168.1.255
         inet6 fe80::1e98:ecff:fe1b:276d  prefixlen 64  scopeid 0x20<link>
         ether 1c:98:ec:1b:27:6d  txqueuelen 1000  (Ethernet)
         RX packets 189315  bytes 9465744 (9.0 MiB)
         RX errors 0  dropped 0  overruns 0  frame 0
         TX packets 302  bytes 30522 (29.8 KiB)
         TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[root at clusterdev01]# virsh iface-list --all
  Name                 State      MAC Address
---------------------------------------------------
  br1                  active     1c:98:ec:1b:27:6d
  br1.600           active     1c:98:ec:1b:27:6d

[root at clusterdev01 sysadmin]# virsh iface-dumpxml br1.600
<interface type='vlan' name='br1.600'>
   <protocol family='ipv4'>
     <ip address='192.168.1.110' prefix='24'/>
   </protocol>
   <protocol family='ipv6'>
     <ip address='fe80::1e98:ecff:fe1b:276d' prefix='64'/>
   </protocol>
   <link state='up'/>
   <vlan tag='600'>
     <interface name='br1'/>
   </vlan>
</interface>

I tried following some suggestions which wrapped the vlan interface in a 
bridge interface, but in ended up trashing the br1.600 interface which 
was originally defined on the host.

Is there a failsafe way to deal with such a situation? Am I doing 
something completely wrong here? In would like br1.600 to behave like 
br1 .....

Any suggestions or advice greatly appreciated.

Richard