We need bridge (brX) interface(s) for linux kvm virtualization.

EXAMPLE FOR 3 VLAN-S

VLAN-s must be defined on Cisco switch

VLAN 10 – IT vlan
VLAN 20 – DMZ vlan
VLAN 30 – guest vlan

Define vlan without ip (L2 switch):

switch# conf t
switch(config)# vlan 10
switch(config-vlan)# name vlan-it
switch(config-vlan)# end
switch# write

Define vlan with ip address (L3 switch):

switch# conf t
switch(config)# interface vlan 10
switch(config-if)# ip adress 192.168.10.1 255.255.255.0
switch(config-if)# description vlan-it
switch(config-if)# end
switch# write

INTERFACE CONFIGURATION ON CISCO SWITCH

Connection to network interface eth0 on linux server for vlan 10 and vlan 30 (trunk connection):

interface GigabitEthernet1/0/30
 description == kvm server IT
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 10,30
 switchport mode trunk

Connection to network interface eth1 on linux server for vlan 20 (trunk connection):

interface GigabitEthernet1/0/31
 description == kvm server DMZ
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 20
 switchport mode trunk

NETWORK CONFIGURATION ON LINUX SERVER (Debian)

linux-server:~# cat /etc/network/interfaces

# The loopback network interface
auto lo
iface lo inet loopback

# VLAN 10 (IT vlan)
auto eth0.10
iface eth0.10 inet manual
        up ifconfig eth0.10 up

# KVM bridge , VLAN 10, via eth0 (management interface)
auto br10
iface br10 inet static
        address xx.xy.xz.10
        netmask xx.xy.xz.0
        network xx.xy.xz.0
        broadcast xx.xy.xz.255
        gateway xx.xy.xz.1
        dns-nameservers 8.8.8.8 4.4.4.4
        dns-search local.domain.com
        bridge_ports    eth0.10 
        bridge_maxwait  5
        bridge_fd       1
        bridge_stp      on

# VLAN 20 (DMZ vlan)
auto eth1.20
iface   eth1.20 inet manual
        up ifconfig eth1.20 up

# KVM bridge, VLAN 20, via eth1
auto br20
iface br20 inet manual
        bridge_ports    eth1.20
        bridge_maxwait  5
        bridge_fd       1
        bridge_stp      on

# VLAN 30 (guest vlan)
auto eth0.30
iface eth0.30 inet manual
        up ifconfig eth0.30 up

# KVM bridge, VLAN 30, via eth0
auto br30
iface br30 inet manual
        bridge_ports    eth0.30
        bridge_maxwait  5
        bridge_fd       1
        bridge_stp      on