Tunnels can be used to do some very unusual and very cool stuff. They can
also make things go horribly wrong when you don't configure them right.
Don't point your default route to a tunnel device unless you know
EXACTLY what you are doing :-). Furthermore, tunneling increases
overhead, because it needs an extra set of IP headers. Typically this is 20
bytes per packet, so if the normal packet size (MTU) on a network is 1500
bytes, a packet that is sent through a tunnel can only be 1480 bytes big.
This is not necessarily a problem, but be sure to read up on IP packet
fragmentation/reassembly when you plan to connect large networks with
tunnels. Oh, and of course, the fastest way to dig a tunnel is to dig at
both sides.
