Originally posted here by journy101
A crossover cable has the send and recieve wires at one end swaped. This is so the data sent out of computer A goes to the recieve on computer B, you don't want a send and send tied together. If you have a hub, router or switch this is taken care of, thats why you would usualy use a straight through.
Just to clarify, the general rule is:

Swtich to Switch (or Router to Router) = use a cross over
NIC to NIC = use a cross over
NIC to Switch (or NIC to Router) = use a straight through

It's easy to tell the difference between the two types. Just hold the two RJ45s at each end next to each other. If the coloured wires are in the same order, its a straight through. If two pairs of the coloured wires are swapped (ie. so they cross over), it's a cross over.

Also, the above definitions of routers vs switches are off the mark. A router is a layer 3 device that routes (usually IP) traffic between two or more networks. A switch is a layer 2 device that is used to minimise collisions on an ethernet network by only passing on frames intended for the MAC client connected to that port. Yes, there are Layer 3 switches which make switching decisions based on network layer data but it's still essentially a data link layer device i.e. it doesn't do any routing.

I don't see the point of placing your hacking lab behind a router unless you intend to use it for basic packet filtering. Placing it behind a switch might give you better throughput if other devices are competing for the same link.