L2TP version 3 VLAN-to-VLAN

For a few days ago I had to find a solution for a customer that could provide VLAN-to-VLAN traffic over Internet between 2 locations. I found a solution which I think was really interesting therefore I want to share it here.

Here are the requirements:

    Host 1 (VPC1) in VLAN X  at location A and Host 2(VPC2) in VLAN X in location B should be able to send Multicast traffic to each other as well as unicast traffic
    Host 3 (VPC3) in VLAN Y  at location A and Host 4(VPC4) in VLAN Y in location B should be able to send Multicast traffic to each other as well as unicast traffic
    Host 2 and Host 4 at location B cannot be configured with a default gateway so they must be in the same broadcast domain as Host 1 and Host 2 respectively in location A
    Host 1/2 traffic should completely be isolated from Host 3/4 traffic

First of all I thought of configuring GRE and multicast routing but then I realized that there would be an issue for unicast traffic as Host 2/4 cannot be configured with a default gateway. So one of my colleague told me to use L2TPv3. I haven’t heard about this feature before. I knew EoMPLS but I did not know  that it was possible to send L2 traffic over Internet.

I used GNS3 (my favorite simulating tool) to test it. Here is the setup  used (I am using cisco 2691 with 12.4(15)T11)

 

Here is an output on how the L2TPv3 encapsulation looks like when I ping from VPC1 to VPC2. As you can see below the Cisco implementation of L2TPv3 uses IPv4 encapsulation with an IP protocol ID of 115. Cisco does not support the IPv4/UDP encapsulation form for L2TPv3  which can have the advantage of being friendlier to applications such as NAT. Moreover IPv4 encapsulation only provides header checksum while UDP also provides payload intergrity.

Show Commands:
show l2tunn session -> Provide state of the tunnel(s). Look for esp state which means established
show l2tunn session all -> Provide more detailed information about the tunnel(s)
show xconnect all -> Provide state of the tunnel(s). Look for up state

Debug commands:

debug vpdn l2x-events
debug vpdn l2x-packets

I attach the partial configuration of R1 and R3 if some people are interested in it: R1-R3-L2TPv3-Config

At first I could not make it work when using VLAN1 then after configuring another VLAN it was working.  I am not sure what is going on when using VLAN1 but maybe it is because Cisco router/switch uses VLAN1 for control traffic (VTP,STP,CDP). If anyone as an idea you are really welcome to write a comment.