Xconnect over VRF Aware L2TPv3 on Cisco ASR Platform

This document describes how the Virtual Routing and Forwarding (VRF) can be used when you configure Layer 2 Tunneling Protocol (L2TP)v3 Xconnect over IP and Multiprotocol Label Switching (MPLS) network.

L2TP is the tunneling protocol used by Internet Service Providers (ISPs) in order to provide Virtual Private Network (VPN) in the dial access space over the internet.

It combines the best of Cisco’s Layer 2 Forwarding (L2F) protocol and Microsoft’s Point-to-Point Tunneling Protocol (PPTP). The main components of L2TP are L2TP Access Controller (LAC) and L2TP Network Server (LNS).

L2TP Access Controller: LAC is an access server connected to Public Switched Telephone Network (PSTN). The LAC is the initiator of incoming calls and the receiver of outgoing calls. It is connected to LNS over LAN or WAN.

L2TP Network Server: LNS is the network server for L2TP protcol where PPP sessions terminate and are authenticated. The LNS is the initiator of outgoing calls and the receiver of incoming calls.

L2TPv2 was designed to carry PPP traffic over IP networks. Network access equipment (DSL, cable modem or dial-up access interfaces) accepted PPP connections from subscribers and tunnelled the PPP sessions to the ISP over L2TP. The new version L2TPv3 is designed to carry any Layer 2 payload in addition to PPP which was the only payload that was supported by version 2.  Specifically, L2TPv3 defines the L2TP protocol for tunneling Layer 2 payloads over an IP core network with the use Layer 2 VPNs. Benefits of this feature include this:

  • L2TPv3 simplifies deployment of VPNs
  • L2TPv3 does not require MPLS
  • L2TPv3 supports Layer 2 tunneling over IP for any payload

Here is the sample configuration of L2TPv3 pseudowire:

2.configure terminal
3.interface type slot/port
4.xconnect peer-ip-address vcid encapsulation l2tpv3pw-class pw-class-name

Now take a look at how L2TPv3 Xconnect behaves when VRF is used. Here is the topology that is used for demonstration in which we Xconnect is configured between CPE and ASR1002 (IP) and ASR1004 (MPLS) with endpoints at ASR1000 in VRF (VRF Aware L2TPv3 is not supported on ASR1000 platform).
Screen Shot 2018-03-22 at 9.27.51 AM.png
We will be discussing below test cases in this post:

This is well explained in below Cisco document by me:


Categories: General, IPv4, MPLS, Routing

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