Look at the RJ45 connector on a cable, holding the flat underside toward you. The Platinum Tools Lanseeker does an excellent job at this. You should only save known good cables, but you can use a basic cable tester with remote to check out continuity and wiring. The first place where you’ll have to figure out which cable is which is when you’re retrieving spare premade cables from your extras box. Hopefully, someone labeled them and identified their use. A fourth type, which has to be mentioned - home made cables with nonstandard pinouts, often non-Ethernet.Crossover type which was necessary to connect computer to computer without any intervening network equipment.Straight through type, connecting to networking equipment such as routers, hubs, and switches, which is the predominant cable type now.Usually light blue, sometimes with a 9-pin RS-232 connector on one end. Rollover type which only looks like an Ethernet cable, but can be useful with Cisco equipment consoles.Ethernet cables, the 8-pin variety which are terminated by an RJ45-style connector, can come in just enough varieties to spread confusion.

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