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Cisco ONS 15310-CL and Cisco ONS 15310-MA Ethernet Card Software Feature and Configuration Guide R8.5
78-18133-01
Chapter 8 Configuring IEEE 802.1Q Tunneling and Layer 2 Protocol Tunneling on the ML-Series Card
Understanding IEEE 802.1Q Tunneling
Customer traffic tagged in the normal way with appropriate VLAN IDs comes from an IEEE 802.1Q
trunk port on the customer device and into a tunnel port on the ML-Series card. The link between the
customer device and the ML-Series card is an asymmetric link because one end is configured as an
IEEE 802.1Q trunk port and the other end is configured as a tunnel port. You assign the tunnel port
interface to an access VLAN ID unique to each customer (Figure 8-1).
Figure 8-1 IEEE 802.1Q Tunnel Ports in a Service-Provider Network
Packets coming from the customer trunk port into the tunnel port on the ML-Series card are normally
IEEE 802.1Q-tagged with an appropriate VLAN ID. The tagged packets remain intact inside the
ML-Series card and, when they exit the trunk port into the service provider network, are encapsulated
with another layer of an IEEE 802.1Q tag (called the metro tag) that contains the VLAN ID unique to
the customer. The original IEEE 802.1Q tag from the customer is preserved in the encapsulated packet.
Therefore, packets entering the service-provider infrastructure are double-tagged, with the outer tag
containing the customer’s access VLAN ID, and the inner VLAN ID being the VLAN of the incoming
traffic.
When the double-tagged packet enters another trunk port in a service provider ML-Series card, the outer
tag is stripped as the packet is processed inside the switch. When the packet exits another trunk port on
the same core switch, the same metro tag is again added to the packet. Figure 8-2 shows the structure of
the double-tagged packet.
Customer A
VLANs 1 to 100
Customer B
VLANs 1 to 200
Customer B
VLANs 1 to 200
Customer A
VLANs 1 to 100
Tunnel port
VLAN 40
Tunnel port
VLAN 40
Trunk
Asymmetric link
Tunnel port
VLAN 30
POS
0
POS
0
Switch_A
SONET STS-N
Switch_B
Fast Ethernet 1
Fast Ethernet 0
Fast Ethernet 1
Fast Ethernet 0
124095
Tunnel port
VLAN 30
ML-Series
ML-Series