ZyXEL Communications VES-1616 - Manual (Page 45)

ZyXEL VES-1616/24FA-5x Series Support Notes
All contents copyright 2008 ZyXEL Communications Corporation. 44
VLAN Stacking Overview
VLAN stacking allows a carrier to offer multiple virtual LANs over a single circuit.
In essence, the carrier creates an Ethernet VPN to tunnel customer VLANs
across its WAN. Thus it helps to avoid name conflicts among customers of
multiple service providers who connect to the same carrier.
VLAN stacking works by assigning two VLAN IDs to each frame header. One is a
"backbone" VLAN ID used by the service provider, the other (up to 4,096 unique
802.1Q VLAN tags) is used by the customers.
The following figure shows a network example.
In this example, company XX and company YY both subscribe to the same ISP
for Internet service. Both companies have an internal VLAN group with VID 1. In
order to prevent VLAN-tagged packets between these two companies from
transmitting to each other’s network, VLAN stacking is implemented in the ISP’s
network. The ISP assigns a service provider VID for each company- company XX
is assigned an SP VID of 30 and company YY is assigned an SP VID of 40.
The following shows the packet flow between Company XX HQ and its branch
Company XX branch
VLAN 30|VLAN 2
VLAN 30|VLAN 2
VLAN 40|VLAN 2
VLAN 40|VLAN 2
VLAN 2
VLAN 2
VLAN 2
VLAN 2
Company XX HQ
Company YY branch
Company YY HQ
1
2
3
Switch
H
Switch
A
Switch
C
Switch
B
Switch
D
Switch
E
Switch G
Switch
F
Port
26
Port
1
Port
1
Port
1
Port
2
Port
27
Port 17
Port 17
Port 17
Port 17
Port 25
Port
25
Port
25
Port 25