DB-9/Cisco RJ-45 Serial Console Adaptors

DB-9/RJ-45 Console Adaptors

An alternative wiring scheme for DB-9/RJ-45 console adaptors that that work with CAT 5 cable and support Cisco RJ-45 consoles

I work with a lot of networking equipment and have always had to carry a boatload of serial cables, gender benders, and adaptors to allow me to connect to console ports on the various devices I encounter. When Cisco moved to RJ-45 console connectors, requiring that stinking "rollover" cable, something inside me rebelled against having to carry another cable, especially one with only a single use (even if it is a very common use).

In 2001, after a long night where I had to string together everything in my bag to console into a Nortel switch, I finally broke down and came up with a more workable solution (for me anyway). The idea was to create a generic set of console adaptors that would:

Permit direct connection to DB-9 DCE and DTE connections
Permit direct connection to Cisco RJ-45 console connectors
Permit connection to DB-25 connectors using "DB-9 to DB-25" adaptors
Use any CAT 5 cable and eliminate hte need for the "rollover" cable

My solution was to specially wire 3 DB-9F/RJ-45 adaptors, one for the "Laptop" end and two for the "Device" end, to work the following way:

The "Laptop" adaptor and a CAT 5 cable will connect directly to a Cisco RJ-45 console port
The "Laptop" adaptor, a CAT 5 cable, and a DTE-wired "Device" adaptor will connect to a DTE console or terminal port
The "Laptop" adaptor, a CAT 5 cable, and a DCE-wired "Device" adaptor will connect to a DCE console or modem port

The wiring diagram (.pdf file) shows the wiring for each adaptor. I purchased DB-9F/RJ45 adaptors with colored shells so I could tell them apart easier (they're each also labelled). The wire colors shown reflect the wires in the adaptors I bought, and also seem to match other adaptors I've used. What's really important is that the pin numbers between DB-9 and RJ-45 match for all 3 adaptors. Also, be careful to correctly identify pin 1 of the RJ-45 socket in the adaptors (Hint: When looking at the "contact side" an RJ-45 connector on a CAT 5 cable, with the plastic "hook" away from your face and the "cable" end of the RJ-45 toward your body, pin 1 is the far left contact).

Since I made my set back in 2001, I haven't found a console that they didn't work with. At this point, I carry the three adaptors, a few CAT 5 cables, one DB-9M/DB-25F adaptor, one DB-9M/DB-9M gender bender, and one DB-25M/DB-25M gender bender, as shown above. I used to carry several cables and a large variety of adaptors, and am now down to 6 devices and a CAT 5 cable. I hope your mileage is as good.

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Copyright 2001-2009, Tim Sharpe. You are free to use this information for personal, non-commerical use without restriction. All rights reserved for commerical, organizational, or government use. Questions or comments to tim@beaststwo.org. Flames to /dev/nul.

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