Cisco 7604 Configuration Manual page 236

Understanding How 802.1Q Tunneling Works
The customer routers are trunk connected, but with 802.1Q tunneling, the service provider routers only
use one service provider VLAN to carry all the customer VLANs, instead of directly carrying all the
customer VLANs.
With 802.1Q tunneling, tagged customer traffic comes from an 802.1Q trunk port on a customer device
and enters the service-provider edge router through a tunnel port. The link between the 802.1Q trunk
port on a customer device and the tunnel port is called an asymmetrical link because one end is
configured as an 802.1Q trunk port and the other end is configured as a tunnel port. You assign the tunnel
port to an access VLAN ID unique to each customer. See
page 17-3.
Figure 17-1 IEEE 802.1Q Tunnel Ports in a Service-Provider Network
802.1Q trunk port
802.1Q trunk port
802.1Q trunk port
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
17-2
Customer A
VLANs 1 to 100
802.1Q trunk port
802.1Q trunk port
Tunnel port
VLAN 30
Tunnel port
VLAN 30
Tunnel port
VLAN 40
Customer B
VLANs 1 to 200
Chapter 17
Figure 17-1 on page 17-2
Service
provider
Tunnel port
VLAN 30
Trunk Trunk
ports ports
Tunnel port
VLAN 40
Trunk
Asymmetric link
Configuring IEEE 802.1Q Tunneling
and Figure 17-2 on
Customer A
VLANs 1 to 100
802.1Q trunk port
802.1Q trunk port
802.1Q trunk port 802.1Q trunk port
Customer B
VLANs 1 to 200
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