Difference between GRE Tunneling and Q-in -Q Tunneling

[Ketan Bheda]

Hi People,

I am so much confused regarding the difference between Q-in-Q tunneling and GRE Tunneling.

I have used Tunneling/VPN to connect the remote locations to provide the full range of voice communication in my infrastructure, via tunneling I am now able to communicate between two different location. But now I came across the another concept called Q-in-Q Tunneling.

I am very well aware, of which devices these two needs to be performed but, rather than that what are the applications does these two technologies have? Where are they used and what is the purpose for q-in-q if I have GRE tunneling with me?

[Joseph W. Doherty · Accepted solution]

GRE tunneling is done at L3, Q-in-Q tunneling is done at L2. Often lower end routers don't support Q-in-Q while lower end switches don't support GRE.

GRE will generally ride across any IP network. Q-in-Q rides across L2 networks that support VLAN tagging.

As to applications that use them, Q-in-Q is used to extend a L2 network across a transit L2 network. GRE is used to "join" L3 networks (such as in your mention of using it for VPNs). The difference is, with Q-in-Q the same VLAN can be in multiple locations, but with GRE the same IP (interior) network is not in multiple locations.

[Ketan Bheda]

Hi Joseph,

Thanks for clarifying this matter.

Putting more lights on it I want to ask some few things regarding this:

-If I setup two infrastructure located at two different location for eg one in Mumbai (HQ) and one in Delhi (Branch office), what can be applicable to set up the communication between two locations GRE Tunneling or Q-in-Q Tunneling ?

-I am connected via ISP by its end device as router, what would be fit to implement in this case GRE Tunneling or Q-in-Q Tunneling ?

- Elaborating myself, I have used GRE Tunneling/VPN to bring up the communication between two location. Can that be possible with Q-in-Q Tunneling?

Please refer the attached file as Network Setup. 

[Joseph W. Doherty · Accepted solution]

Across the Internet, as in your question, you would need to use a L3 tunneling protocol such as GRE or an IPSec protocol (or for L2, something like l2tpv3).

To use Q-in-Q, you would need a transit network that supports it. MetroE service providers often do.

Understand what Q-in-Q is - it's double tagged L2 Ethernet frames.

The advantages of Q-in-Q are: it can extend a L2 VLAN and, unlike GRE, it extends the frame i.e. it doesn't need to "steal" some of your data space (unlike GRE which needs 24 bytes from your packet).

[Ketan Bheda]

Hi Joseph,

Thanks once again for clarification.

Just want to add few things here and please correct me if I am wrong.

It can be said as:

-We would use Q-in-Q Tunneling, only if we have our end device as a L3 Switch connected to the same of  ISP, thus allowing us a L2 extension in between different location.

-We would use GRE Tunneling only if our end device would a IOS Router connected with the same of ISP, thus allowing us to use L3 Tunneling concept. 

[Joseph W. Doherty · Accepted solution]

Again, unlikely an ISP would provide Q-in-Q because it requires L2 support and the Internet is L3.

Unsure a "router" would support Q-in-Q, but you might find it supported on a L2 or L3 switch, again because it's used with VLANs.

Some L3 switches also support GRE tunnels. Across the Internet, a GRE tunnel should flow independent of ISPs.

For Q-in-Q, it's possible you could use different providers, end-to-end, but usually you only have one.

[Ketan Bheda]

Hi Joseph, 

Thank you so much once again for clarification. 

[aain]

have you configured Qin Q ? do you have a config guide