Chapter 16. VPNs, Tunneling, and Overlay Networks

Moving on to layers 3 and 4 of the protocol reference model, this chapter introduces some special-purpose networking features: how networks can be overlaid or tunneled . In networking, tunneling is the encapsulation of a packet from one protocol to another one at the same or higher layer. Among application-specific communication networking cases, virtual private networks (VPNs) and multiprotocol label switching (MPLS) networks are two important and popular ones discussed in this chapter. These two network infrastructures can also be tied together for certain applications. The topics covered in of this chapter are

• Virtual private networks (VPNs)

• Multiprotocol label switching (MPLS)

• Overlay networks

A VPN is a networking infrastructure whereby a private network makes use of the public network. A VPN maintains privacy by using tunneling protocols and security procedures. The two types of VPNs, each determined by its method of tunneling, are remote access and site to site .

MPLS networks are a good example of VPNs. In MPLS, multiple labels can be combined in a packet to form a header for efficient tunneling. The Label Distribution Protocol (LDP) is a set of rules by which routers exchange information effectively. MPLS uses traffic engineering for efficient link bandwidth assignments. Such networks operate by establishing a secure tunnel over a public network. Finally, we look at overlay networks . An overlay network is a computer network that creates a virtual topology on top of the physical topology of the public network.