L2 over L3 using GRE

[eab]

Hello,

I'd like to create a tunnel in order to have L2 connectivity over an L3 network (I want to have the same subnet on both ends of the tunnel).
I've looked at some examples on the net; however, they all use L2TPv3 and I don't have the license to do pseudowire.

Is it possible to achieve that using a GRE tunnel?

I don't need encryption as it is a private network. I'm using two ASR920.

Thanks in advance,

[David Ruess]

Hello,

A GRE tunnel is L3 (IP) protocol. You might be able to accomplish what you need configuring/using VXLANS.

-David

[MHM Cisco World]

...

[Richard Burts]

The suggestion of NAT to allow the same subnet to be used at both locations is interesting. But if I am understanding the original post correctly the objective is to have a L2 connection between sites. This suggests that a device at one site should be able to arp for a device at the other site. And NAT does not accomplish that.

The basic problem here is that GRE tunnels generally operate as L3 links, with the tunnel having its own IP subnet while devices at both ends have their own IP subnets. There is one option that you could consider, if your platforms support it. You might be able to enable bridging on the GRE interfaces by configuring Concurrent Routing and Bridging and putting both the GRE tunnel and the Lan interface into the bridge group. Note that this is officially "not supported". This means that it might work. But if something does not work as you expect Cisco has no responsibility to respond to that. It is fine for a lab and for learning purposes, but I would be very reluctant to do this in a live environment.

[MHM Cisco World]

Thanks @Richard Burts alot.

[Richard Burts]

You are welcome. And you are right to suggest l2tp. That really is the optimum solution for what they want to accomplish. But in the original post he states that licensing issues prevent him from implementing this. So if this functionality is important then perhaps a license upgrade (or platform upgrade) may be the solution.

[MHM Cisco World]

Using IPSec with overlapping subnet 
Using L2TP <- need license as you mention