NON-MPLS Layer 2 VPN – L2TPv3 (Layer 2 Tunneling Protocol) review, what exactly it is, and how it works! (No lab)

L2TP-Tunnel-Data-Frame-Format

The above graphic is an L2TPv3 Frame that is essentially connected to a cloud like an MPLS Provider network, though it is not an MPLS Tech like AToM or EoM, it does work very similar in the way that it is Layer 2 Transport of data through a Provider Network.

From what I am gathering L2TPv2 is used mainly by PPPoE subscribers to make a Layer 2 PPP Encapsulated Tunnel from Point A to Point B, while L2TPv3 is a “Psuedowire” type of VPN Tunneling that is an alternative to MPLS.

Whereas a “customer” might use v2, a carrier would use v3, as a way to engineer traffic via L2TP through a carrier network using both Control and Data packets that are tunneled between “Provider Edge” devices called LCCE’s or L2TP Control Connection Endpoints however most people will refer to these simple as Provider Edges.

An “L2TP Session” is used to describe this Control Connection between the two Provider Edge (or LCCE) Endpoints, with 3 variations of connection for L2TP:

  • Manual
  • Manual w/ Keep Alives
  • Dynamic

Some configuration examples from the Provider Edge router

“show l2tp session” on Provider Edge for details on Session Information

“sh l2tp tunnel” to see Tunnel information

Actual configuration on PE:

psuedowire-class eth1000
 encapsulation l2tpv3
 protocol l3tpv3 l2tp_class1
 ip local interface loopback101
 xconnect 192.168.10.100 200 encap l2tpv3 pw-class eth100

That again wraps up this brief look at a Layer 2 Tunneling Protocol

This cannot be labbed outside of Cisco VIRL so I cannot lab this concept, but wanted to just post something up in regards, so that it has been covered – Until next time!

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