Patch cables can come in two different wiring applications: straight-through and crossover. The type of cable that is required depends on the application. Straight-through Ethernet cables are the most commonly used.
Cable typeTypical application Straight-through
Between a computer and a modem, router, or switch
CAT5/CAT6 peripheral extenders
Between other dissimilar networking equipment
Crossover
Between two computers
Between two similar networking devices
Crossover cables use two different wiring standards: one end uses the T568A wiring standard, and the other end uses the T568B wiring standard. To determine if you have a straight-through or crossover cable, compare the Ethernet cables to see if the colors are wired in the same order on each end. For more information on Ethernet wiring standards, refer to the following FAQ: http://www.startech.com/faq/network_cables_a_vs_b_pinout.
Many modern network devices support Auto MDI-X, which automatically negotiates which wiring standard is required. For example, a computer with Auto MDI-X can use either a straight-through or crossover cable for any application.