Chapter 4. Layer 2 VPNs

Layer 2 virtual private network (VPN) is perhaps the most overused term in the networking industry when it comes to MPLS networks. It has a different meaning for everyone. However, this term has been around since the days of both Frame Relay networks and Asynchronous Transfer Mode (ATM), which are commonly deployed L2 technologies.

Perhaps a simplistic way to describe Layer 2 VPNs is like this: They are a group of sites connected together at Layer 2 by point-to-point ATM VCs, Frame Relay data link connection identifiers (DLCI), or Point-to-Point Protocol (PPP) sessions. The most important concept is that IP routing is done at the edge of the Layer 2 network. As mentioned earlier, the service that is delivered to the end ...

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