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802.1Q Tunnel Ports in a Service-Provider Network

sarahr202
Level 5
Level 5

Hi everybody

I am trying to understand 802.1q tunneling or Qin Q.   Please consider the following link for my question. I quote from the link the pertinent parts for my question.

http://www.cisco.com/en/US/docs/switches/metro/me3400e/software/release/12.2_44_ey/configuration/guide/swtunnel.html

Understanding 802.1Q Tunneling

Packets coming from the customer trunk port into the tunnel port on the  service-provider edge switch are normally 802.1Q-tagged with the  appropriate VLAN ID. The the tagged packets remain intact inside the  switch and when they exit the trunk port into the service-provider  network, they are encapsulated with another layer of an 802.1Q tag  (called the metro tag) that contains the VLAN  ID that is unique to the customer. The original customer 802.1Q tag is  preserved in the encapsulated packet. Therefore, packets entering the  service-provider network are double-tagged, with the outer (metro) tag  containing the customer's access VLAN ID, and the inner VLAN ID being  that of the incoming traffic.

When the double-tagged packet enters another trunk port in a service-provider core switch,  the outer tag is stripped as the switch processes the packet. When the  packet exits another trunk port on the same core switch, the same metro  tag is again added to the packet. Figure 14-2 shows the tag structures of the double-tagged packets


My example:

Customer Sw1-------tunnelport-SW2 (at SP)----trunk----Sw3------------Sw4------Sw5-tunnel port---------SW7(Customer7)

Cvlan is vlan2

while Svlan is 6.

Customer sw1 sends a frame tagged with vlan 2 ( Cvlan) to Sw2 at SP

Sw2 receives the frame. Sw2 will process the frame and attaches vlan6 ( Svlan) and sends it out of trunk to Sw3.

Here is my question.

What exactly Sw2 uses to determine the this frame should be send out of trunk to sw3?

For example, In CCNP switch exam, I learned the switch will check the destination mac against the mac table which in turn tell the switch which port( access/ trunk) the frame should be sent out.

But here in 802.1q tuneling, how does sw2 determine to use trunk port connected to sw3 to send the frame out?

Have a great weekend.

1 Reply 1

Marwan ALshawi
VIP Alumni
VIP Alumni

for .1q QinQ the L2 switching concept still the same the switch flood to ports in the same vlan in SP case will flood it using the outer VLAN ID to learn the unknown dest MAC

other option is to tunnel at  SW2 to SW4 using L2VPN technology

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