Wireless Hacks

Tunneling: IPIP Encapsulation

IP tunneling with the Linux IPIP driver.

If you have never worked with IP tunneling before, you might want to take a look at the Advanced Router HOWTO (http://www.tldp.org/HOWTO/Adv-Routing-HOWTO/) before continuing. Essentially, an IP tunnel is much like a VPN, except that not every IP tunnel involves encryption. A machine that is “tunneled” into another network has a virtual interface configured with an IP address that isn’t local, but exists on a remote network. Usually, all (or most) network traffic is routed down this tunnel, so remote clients appear to exist on the network as if they were local. This can be used to allow clients from the Internet to access private network services, or more generally, to connect to any two private networks together using the Internet to carry the tunnel traffic.

If you want to perform simple IP-within-IP tunneling between two machines, you might try IPIP. It is probably the simplest tunnel protocol available, and also works with *BSD, Solaris, and even Windows. Note that IPIP is simply a tunneling protocol, and does not involve any sort of encryption. It is also only capable of tunneling unicast packets; if you need to tunnel multicast traffic, take a look at GRE tunneling [Hack #55].

Before we rush right into our first tunnel, you need a copy of the advanced routing tools (specifically the ip utility.) You can get the latest authoritative copy from ftp://ftp.inr.ac.ru/ip-routing/. Be warned, the advanced routing ...