KVM networking with different VLANS

Question

I'm currently running KVM on CentOS 6 server, and have bridged networking setup for the first subnet that's assigned to the server.

When I'm trying to use the other subnet, that's using a different gateway, would I need to create new br0 (br1) device for the VLAN or new eth0:1 connection ?

The subnet that's being used as the default would be: 77.XX.XX.9/29

And I have several assigned of the same block size: 216.XX.XX.143/29 216.XX.XX.182/29

Thank you!

Answer 1

You need to create an interface that's connected to the vlan (like "eth1.2102" for vlan 2102). Then you create a bridge ("br2102") that has the vlan interface as a member. You can use the /etc/sysconfig/network-scripts entries to do that, don't assign IPs to those interfaces. Then use the bridge interface in the qemu/kvm configration as the interface for the virtual machine.

Config example (Tested on Centos 6.0):

ifcfg-eth1:

DEVICE=eth1
BOOTPROTO=static
BROADCAST=0.0.0.0
HWADDR=00:15:17:dc:ff:ff # use your mac here
IPADDR=0.0.0.0
NETMASK=0.0.0.0
NETWORK=0.0.0.0
ONBOOT=yes
IPV6INIT=no
NOZEROCONF=yes
TYPE=Ethernet

ifcfg-eth1.2102:

VLAN=yes
DEVICE=eth1.2102
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=none
IPV6INIT=no
IPADDR=0.0.0.0
NETMASK=0.0.0.0
NETWORK=0.0.0.0
BRIDGE=br2102

ifcfg-br2102:

DEVICE=br2102
TYPE=Bridge
ONBOOT=yes
# BOOTPROTO=none
BOOTPROTO=static
IPADDR=
NETMASK=

"ifup br2102" should bring up all those interfaces. Be sure to have this in /etc/sysctl.conf:

net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0

Troubleshooting: use "tcpdump -i eth1.2102 -n" and tcpdump -i br2102 -n" to see the traffic on those interfaces. "brctl show" is handy to see the bridge config with the virtual machine interface on the bridge added after startup. PXE booting has a problem, you need to interrupt at the PXE prompt for around 10 seconds before the interface is available. Otherwise the PXE rom doesn't get an IP.