How to build a DB9-to-RJ45 serial cable

This type of cable has a female DB9 connector on one end and a male RJ45 plug on the other. It is used to connect to the serial console of older Cisco devices and Sun gear, among others.

RJ45 pinRJ45 colorDB9 pin
1Blue8
2Orange6
3Black2
4Red5
5Green5*
6Yellow3
7Brown4
8White/gray7

* According to official Sun manuals this pin ALSO needs to be connected to pin 5 on the DB9 end. According to some other documentation I found it is not necessary to connect it at all. I didn’t connect it and the cable works fine for me.

For the ethernet cable, it is important to use a regular one. This is also called a patch cable or straight-through cable. It is the type you would usually use between a server and a switch, for example.

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