IP: tunneling

modulename: ipip.ko

configname: CONFIG_NET_IPIP

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>IP: tunneling
In linux kernel since version 2.6.12  
Tunneling means encapsulating data of one protocol type within
another protocol and sending it over a channel that understands the
encapsulating protocol. This particular tunneling driver implements
encapsulation of IP within IP, which sounds kind of pointless, but
can be useful if you want to make your (or some other) machine
appear on a different network than it physically is, or to use
mobile-IP facilities (allowing laptops to seamlessly move between
networks without changing their IP addresses).

Saying Y to this option will produce two modules ( = code which can
be inserted in and removed from the running kernel whenever you
want). Most people won't need this and can say N.

source code: