©
Anritsu MU909060A-E-F-1
Application Note
VLAN Stacking or Q-in-Q
Where is it and why?
MT9090A/MU909060A
Network Master GigE
By Stuart Whitehead
Background
Telecom operators test their networks in many different ways for many different reasons.
When testing an Ethernet network it’s important to note what type of testing is required and where it’s required, this document
aims to explain if testing VLAN Stacking is required in the Access network.
In order to do this the document will also overview the technologies involved and the reasons why people test in different areas.
Q-in-Q or VLAN Stacking are common terms used by today’s telecom operators which are the same thing. For convenience
we will reference it as “VLAN Stacking” for the rest of this document.
First let’s quickly look at the difference between VLAN and VLAN stacking.
VLAN
Where does a VLAN come from?
The IEEE standard 802.1Q which was first standardized in Dec 1998 and has since been revised and referenced many times.
The full standard can be downloaded from the IEEE website at http://www.ieee.org and there are many websites which explain
the standard in details including http://en.wikipedia.org/wiki/IEEE_802.1Q, for comprehensive and definitive details you
should always reference the standard itself.
What is a VLAN?
A VLAN is a Virtual Local Area Network which allows the network LAN to be broken
down into more logical networks simplifying management of the network and allowing
configuration and traffic priority across the network. It also has the effect of increasing
security, reducing broadcast traffic and better management of areas such as traffic flow.
VLAN Stacking
Where does VLAN Stacking come from?
VLAN Stacking comes from the IEEE Standard 802.1.ad which was first standardized in Dec 2005. The full standard can be
downloaded from the IEEE website at http://www.ieee.org and there are also many other websites that offer an overview such
as http://en.wikipedia.org/wiki/QinQ. Once again the definitive reference point should be the standard itself. This standard is
very closely related to the VLAN standard as it is all about placing one VLAN inside another (or on top of). This is why the
name VLAN Stacking is often used and because the VLAN standard ends in the letter “q” it is often called Q-in-Q.
What is VLAN Stacking?
VLAN allows the user to better manage his network and prioritize this traffic
though the network but for the service provider or telecom operator this
meant multiple connections from one customer. The telecom operator is
normally interested in having a single connection for each user. VLAN
Stacking allows all traffic from a single user to transfer the telecom network
combined in one logical group.
Figure 1. LAN with 3 VLAN’s inside.
Figure 2. LAN with 2 Staked VLAN’s each with 2
VLAN’s inside.