MPLS based Layer2 VPNs: Extending your Intranet

Layer2 VPNs are a fast emerging, simple and cost effective alternative to traditional VPN solutions like Frame-Relay and ATM. Networks with abundant capacity and powered by MPLS (multi-protocol label switching) at the core are now available to transport data traffic transparently and privately across a shared public network.

Corporates stand to greatly benefit by these MPLS-based layer2 VPN solutions as they are identical to other more traditional layer2 VPNs (Like Frame-Relay and ATM). They are easy to migrate and rely on the service provider only for connectivity. Apart from this, they also stand to benefit from the flexibility offered to run their own routing protocols. Also, they can retain.

their existing security policies as Layer2 connections between two IP connected nodes. This is done without any knowledge of the underlying network used to deliver them.

The New Standards

AToM (Any Transport over MPLS) and L2TPv3 (Layer2 Tunneling Protocol Version 3) are two standards, which are fast gaining popularity as they enable service providers to offer Frame Relay, ATM, Ethernet, and Virtual Leased Line services to customers over a shared public IP/MPLS (Core) network. Service providers can choose between any of the two standards as both offer exactly the same functionality although, AtoM based MPLS networks are typically faster to implement and a little more flexible than L2TPv3 based MPLS.

These standards provide support for point-topoint connectivity for several media encapsulations, like 802.1Q virtual LAN (VLAN), Cisco High-Level Data Link Control (HDLC), Ethernet, Frame Relay, Packet over SONET (POS), and Point-to-Point Protocol (PPP) This provides a great convenience to customers as it reduces the need for multiple Private Leased Circuits while giving them a similar service at much lower costs and with superior redundancies. With the virtual leased line service, the customers would typically connect to the Provider Edge over serial interfaces, which form the ingress and egress points of the L2TPv3 tunnel or a Virtual Circuit in the case of AToM. The service provider maintains IP connectivity between Provider-Edge routers using standard routing protocols.

It’s getting to be as good as one could ask for; a virtual leased line service on a MPLS/IP network without any change in the customer premises equipment!

– Srinivasan CR, General Manager, Technology, Sify