Overview

Tunneling is an encapsulation technology: one network protocol encapsulates packets of another network protocol and transfers them over a virtual point-to-point connection. The virtual connection is called a tunnel. Packets are encapsulated and de-encapsulated at both ends of a tunnel. Tunneling refers to the whole process from data encapsulation to data transfer to data de-encapsulation.

Tunneling provides the following features:

• Transition techniques, such as IPv6 over IPv4 tunneling, to interconnect IPv4 and IPv6 networks.

• Virtual Private Networks (VPNs) for guaranteeing communication security, such as IPv4 over IPv4 tunneling, IPv4/IPv6 over IPv6 tunneling, Generic Routing Encapsulation (GRE), Dynamic Virtual Private Network (DVPN), and IPsec tunneling.

• Traffic engineering, such as Multiprotocol Label Switching traffic engineering (MPLS TE) to prevent network congestion.

Unless otherwise specified, the term "tunnel" used throughout this chapter refers to an IPv6 over IPv4, IPv4 over IPv4, IPv4 over IPv6, or IPv6 over IPv6 tunnel.