How-To: Configuring Q-in-Q Between Two EX3300 Devices

By Christian Scholz (chsjuniper) posted 01-31-2017 00:55

You can use the  EX3300 Q-in-Q configuration presented in the attachment to configure Q-in-Q between two EX3300 devices.
Note: All devices are running Junos OS 12.3R12.4.
The goal of this PoC is to transport customer VLANs from side A to side B without having to add them inside the transit network.
First, configure the Q-in-Q switches (that is, switches that do the Q-in-Q-ing)---in this example, two EX3300 devices.
Note: Do not  forget to add a license first because Q-in-Q is license based on the EX3300 device.
In the next step, configure the transit switch or switches.
This device or these devices must not be aware of any Q-in-Q or customer VLANs at all.
In this example, another EX3300 device was used just to show that no special configuration is needed.
After the setup of the Q-in-Q is completed, two  switches as "client devices” were added pinging each other in VLAN 10 successfully. Of course, more customer VLANs can be added according to the needs of your network.



Q-in-Q EX3300 PoC.txt


Depending on your interface configuration, you might need to adjust the MTU value on your trunk or access ports to accommodate the 4 bytes used for the tag added by Q-in-Q tunneling.


For example, if you use the default MTU value of 1514 bytes on your access and trunk ports, you need to make one of the following adjustments:

  • Reduce the MTU on the access links by at least 4 bytes so that the frames do not exceed the MTU of the trunk link when S-VLAN tags are added.
  • Increase the MTU on the trunk link so that the link can handle the larger frame size.

We use Jumbo-MTU on all of our Trunk-Ports because the Telephone-System needs an MTU of around 7000 (odd I know).

02-18-2017 13:16

Hi!!, i have a problem with qinq. The MTU is limit, how change the value of 1476byte to 1520 or more? This limit of 1476 byte is a big problem for some apps(layer 7).