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Network Configuration—TunnelingWhen talking about tunneling, different definitions come to people's minds.Basically, tunneling is transmitting data that is encapsulated into a pipe, over apublic network (for example, the Internet).However, there are different methods to tunnel data over a public network fordifferent approaches. For example, when security is a concern, tunnel protocolswith cryptography are more favorable. But when performance has higher priority,protocols with lower packet overheads will be chosen.FreeBSD 7 has a built-in support for a number of important tunneling protocols,although there are also many third-party applications in FreeBSD packages thatsupport more tunneling protocols.A list of supported tunneling protocols is shown in the following table:Tunneling protocolGREIPSECNOSGIFDescriptionRFC 1701 and 1702—Generic Routing EncapsulationRFC 4301—Cryptographically-based security for IPv4 and IPv6Cisco compatible IP-in-IP tunneling—also known as KA9QGeneric tunnel interface from WIDE project to tunnel IPv[46]over IPv[46]This chapter introduces the manipulation of tunnel interfaces in the FreeBSD 7operating system.