quicktip: console cables


Whether you’re an operations or network engineer, or a hobbyist tinkering in the homelab, there’s a good chance that you’ll have need of a console cable at some point in your efforts.

Way back when I used to keep a lot of old Sun hardware around, this was pretty easy. I had what was known as a null modem cable with a DB9 serial connector on both ends. I also had a DB9 to DB25 serial converter. This pretty much had my bases covered.

That was in the 20th century. Today the landscape has changed just a little bit. Thankfully, it seems that most vendors have standardized on the RJ45 connector. What they haven’t standardized on is the pinout. I’ll give you a combination that will work for most modern equipment, though.

Since most of us have laptops now, and all laptops have some flavor of USB, we’ll forget about the old school DB9 and DB25 connectors. What we’ll go with is USB on one end, RJ45 on the other, and is known as a rollover cable. This configuration will get you into most modern Cisco hardware, and anything else that wants a rollover cable. But what about other hardware that wants a straight through cable? Easy: attach a rollover converter to a rollover cable and you’ve got a straight through cable.

I’ll give you an easy shopping list:

Using this is super easy. If you ls /dev/tty.* you’ll see something that looks like /dev/tty.usbserial-AL00B27G (and any paired Bluetooth devices) as a result. I use this on my Macbook with a command line tool like screen or minicom as the terminal emulator. screen should have come with your Mac or Linux laptop, so it’s the easiest to get started with. screen /dev/tty.usbserial-AL00B27G should get you connected. The <CTRL>+<A>, <CTRL>+<\> key sequence will quit out of screen.

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