Posted on September 14, 2017 7:42 am
 |  Asked by Steve Vernau
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we are looking at using our DCS-7050SX-64-R to connect to cloud providers via a layer 2 service and this requires QinQ.

The outer (S) vlan is for the layer 2 service to use to know where to forward the frame (ie which cloud provider instance, then  outer tag is stripped and frame is forwarded) and the inner (c ) tag is needed by cloud provider to connect to their virtual routers.

 In Cisco you can do this one once switch:

 encapsulation dot1q 101 seconddot1q 1001



How can I do this on an Arista, the “second-dot1q” command does not exist and I have spent ages looking into this and can’t figure out how.

I think I could maybe get one arista sending c tagged packet via a trunk port into another arista’s dot1q-tunnel mode port but this seems messy as it relies on two switches to be up (and I’m not even sure if this will work)


Posted by Ritika Adlakha
Answered on September 19, 2017 5:03 am

Hi Steve,

For platform DCS-7050SX-64-R, The Q-in-Q feature is implemented whereas the Selective Q-in-Q is not supported. Let’s take the following scenario for understanding the implementation of Q-in-Q on 7050SX devices:

+———-+      +———-+     +———-+      +———-+
|          |T    A|          |T   T|          |A    T|          |
| switch1  +——+ switch2  +—–+ switch3  +——+ switch4  |
|          |1   2||          |3   4|          ||5   6|          |
+———-+     +———–+     +———–+     +———-+
                 |                             |
                 |                             |
                 v                             v

           dot1q-tunnel                  dot1q-tunnel

                                               T – TRUNK PORT

                                               A – ACCESS PORT


On Et 1 :
switchport mode trunk
switchport trunk allowed vlan 2 
On Et 2 :
Switchport access vlan 200
switchport mode dot1q-tunnel
On Et 3 and Et 4:
Switchport mode trunk
On Et 5 :
Switchport access vlan 200
switchport mode dot1q-tunnel
On Et 6:
Switchport mode trunk
switchport trunk allowed vlan 2 

From Et1, the traffic will be tagged with the respective vlan for example vlan 2 (inner C-tag) here and will hit et2 where the dot1q tunnel is configured. On et3 ,When the traffic is inspected, It will be tagged with the outer (s) tag.The traffic will flow through tunnel and then the outer (s) Vlan tag is stripped off when it passes through the access port Et 5 and the trunk port Et 6 will receive traffic for the expected vlan i.e Vlan 2 in this case. 

This is the general implementation of Q-in-Q on 7050SX.The specific mapping of the  inner tags to the outer tags is unfortunately not supported in this platform.


Answered on June 26, 2020 9:40 am

As I see in the supported-features page, Selective Q-in-Q is supported on 7050X switches. But how to configure it?

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