Q-in-Q  - проброс VLAN внутри  другого VLAN.

host1:

   vconfig set_name_type VLAN_PLUS_VID_NO_PAD
   vconfig add eth0 4
   ifconfig vlan4 10.1.1.1 netmask 255.255.255.0 up
   vconfig add vlan4 8
   ifconfig vlan8 192.168.1.1 netmask 255.255.255.0 up

host2:

   vconfig set_name_type VLAN_PLUS_VID_NO_PAD
   vconfig add eth0 4
   ifconfig vlan4 10.1.1.2 netmask 255.255.255.0 up
   vconfig add vlan4 8
   ifconfig vlan8 192.168.1.2 netmask 255.255.255.0 up

ragahost ~ # ping 192.168.1.2
PING 192.168.1.2 (192.168.1.2) 56(84) bytes of data.
64 bytes from 192.168.1.2: icmp_seq=1 ttl=64 time=0.820 ms

ragahost ~ # tcpdump -e -i eth0
22:40:47.297489 00:0e:0c:9b:fa:ce (oui Unknown) > 00:13:d4:8b:c8:b6 (oui Unknown), 
ethertype 802.1Q (0x8100), length 106: vlan 4, p 0, ethertype 802.1Q, vlan 8, p 0, 
ethertype IPv4, 192.168.1.2 > 192.168.1.1: ICMP echo request, id 64531, seq 146, length 64