Cable type for connecting two routers

Unless the ports are auto-sensing, the receive pins must match up with the transmit pins and this will require a crossover cable.

The rule of thumb is: when connecting similar devices (router to router, computer to computer) use a crossover cable. When connecting dissimilar devices (router to switch, computer to switch) use a straight through cable.

Of course Auto-MDIX and designated uplink ports can make this a moot point, and can make it confusing at times.