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It has always seemed a bit strange to me that the console ports on networking gear are 8P8C (popularly referred to as "RJ45" even though that's not strictly applicable here) connectors and require an adapter to connect to a DE9 serial port. What is the reason for this? Is it entirely to make better use of panel real estate?

tgies
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    The cynical would say it was originally to allow Cisco to sell extra cables and adapters. – David Schwartz Jan 04 '13 at 02:01
  • @David: Well, probably, but I guess my real question is "what is the _stated_ reason". :) – tgies Jan 04 '13 at 02:03
  • To sell extra cables and adapters, and save 17 cents over the cost of replacing it with a standard that's actually used anywhere in the last decade (USB for example). – HopelessN00b Jan 04 '13 at 02:03
  • I don't know if "to sell cables" makes sense as a serious answer; Cisco gear always includes the cable, and if you're buying a replacement you are probably going to buy it from a third party who charges a quarter of Cisco's price. – tgies Jan 04 '13 at 02:05
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    Well, on terminal servers with 10 or more ports, it does save a huge amount of panel real estate. And if you're going to connect the network switch to a terminal server (which was the usual setup), an RJ45 console cable was what you'd use, not an adapter. – David Schwartz Jan 04 '13 at 02:06
  • @DavidSchwartz: I hadn't considered the terminal server angle. Good point. – tgies Jan 04 '13 at 02:10
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    I would guess that RJ45 sockets are cheaper then DB9. Cisco, just have a huge volume for RJ45 sockets. – Zoredache Jan 04 '13 at 05:47

2 Answers2

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Density, cost and the smaller form factor are probably the primary reasons.

Look at a Cisco 2960 48-port front panel, for instance... I think the RJ45 is a better bet for serial than a DB-9 in that case.

Also having easy ability to pin-out for Cat5 runs to serial console/terminal servers.

ewwhite
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  • Probably, but I'm really hoping someone can provide a more or less "definitive" answer backed by reliable sources. – tgies Jan 04 '13 at 02:08
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Out Of Band management is the only thing I can think of. A specific port that gets you into the device that doesn't rely on the communications-plane being managed. In the beginning, all comms techs HAD serial laying about, and it was easy: just plug the port into your serial terminal and configure. No mucking about with Ethernet, DHCP, BootP, or RARP, or figuring out what IP the switch auto-configures for itself.

And then inertia happened.

sysadmin1138
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