CCNP Routing and Switching ROUTE 300-101 Official Cert Guide

MPLS-Based Virtual Private Networks

Multiprotocol Label Switching (MPLS) is a technology commonly used by service providers, although many large enterprises also use MPLS for their backbone network. MPLS makes forwarding decisions based on labels rather than IP addresses. Specifically, a 32-bit label is inserted between a frame’s Layer 2 and Layer 3 headers. As a result, an MPLS header is often called a shim header, because it is stuck in between two existing headers.

MPLS-based VPNs can be grouped into one of two primary categories:

Layer 2 MPLS VPNs

Layer 3 MPLS VPNs

These two approaches are discussed further in the section “MPLS VPN,” later ...