Is it for IP/Lan communication or is it Serial/RS232 over RJ45? If it's for IP/Lan, the high speed signal and noise rejection/specification relies on the twisted pairs. So I would not try running LAN/IP network over 9pin serial. Depending on distance it might work (like if it's short), but seems like a bad idea to me. If this is just normal serial RS232 that uses RJ45 as a connection type, that should work fine. Answer from mistakenotmy on reddit.com
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Amazon
amazon.com › COOSO-Serial-Female-Ethernet-Console › dp › B01MF9F7HF
Amazon.com: LFHUKEJI RJ45 to RS232, DB9 9-Pin Serial Port Male to RJ45 Cat5 Ethernet LAN Console 3.3Ft : Electronics
DB9 RS232 male to RJ45 female console cable for TCP/IP network interface with the doual-way conversion, with the serial port network function, support serial data and network data bi-directional transparent transmission
Discussions

Confused about proper pinout with an RJ45 to DB9 adapter
I am attempting to control a device with RS232 commands. The device has a control box that accepts RJ45 cable. I am sending my commands via a Global Cache iTach WF2SL device which has a DB9 serial port. I am attempting to connect the two devices using a Cat-6 T-568B cable, and a RJ45 to DB9 adapter. More on community.spiceworks.com
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9
4
March 18, 2025
Serial Console over RJ45 Ethernet-Patchpanels / RS232-Ethernet-Pinout?
You don't need to do anything special on the patch/extension side. Any RJ45 coupler/patch will result in no wire transposition. Only one cable in the chain needs to be a rollover, the rest can be Ethernet-spec. So: ACS - Rollover - Anything - Switch This is similar to how you can extend your laptop rollover cable with a standard female-female coupler and patch cable. Get some flat, 8-wire cable to make your rollover cables if you want to make your life easy and ditch anything DB9 unless necessary. I know this from direct experience. We use Avocent everywhere. Feel free to ask if you have more questions. More on reddit.com
🌐 r/networking
5
1
July 5, 2021
programming - Serial Communication with rs232/485 and rj45 - Electrical Engineering Stack Exchange
Bring the best of human thought and AI automation together at your work. Explore Stack Internal ... They both have rs232/rs485 capabilities, just depends on a switch on the back of the terminal and both connections are with a rj45 jack (I will attach relevant manual). And connect via a RJ45 cable, ... More on electronics.stackexchange.com
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May 20, 2015
Can I put RJ45 connectors on RS232 9-pin cable?
Is it for IP/Lan communication or is it Serial/RS232 over RJ45? If it's for IP/Lan, the high speed signal and noise rejection/specification relies on the twisted pairs. So I would not try running LAN/IP network over 9pin serial. Depending on distance it might work (like if it's short), but seems like a bad idea to me. If this is just normal serial RS232 that uses RJ45 as a connection type, that should work fine. More on reddit.com
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11
4
December 13, 2021
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Antaira
antaira.com › products › Serial-Cables › CB-RJ45-DB9M-90
RJ45 to DB9 Male Serial Cable - 90cm
RJ45 to DB9 Male Serial Cable - 90cm | Antaira · To request more information regarding our products, please fill out the following online form and a customer service representative will contact you immediately. Fields marked (*) are required. Thank you
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Waveshare
waveshare.com › wiki › RS232-TO-RJ45-Console-Cable
RS232-TO-RJ45-Console-Cable - Waveshare Wiki
Console communication cable, adopts high-purity oxygen-free copper core, suitable for router, switch, and other devices with console (RJ5) port from brands such as Cisco, etc. Suitable for desktop PC, laptop, tablet PC, and other devices with ...
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eBay
ebay.com › electronics › computers/tablets & networking › computer cables & connectors › networking cables & adapters › other networking cables
Serial RS232 to Ethernet RJ45 Adapter Cable FAST USA SHIPPING | eBay
Serial RS232 to Ethernet RJ45 Adapter Cable FAST USA SHIPPING
Find many great new & used options and get the best deals for Serial RS232 to Ethernet RJ45 Adapter Cable FAST USA SHIPPING at the best online prices at eBay! Free shipping for many products!
Price   $10.00
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Eaton
tripplite.eaton.com › products catalog › network adapters › p44089ff
DB9 to RJ45 Modular Serial Adapter, RS-232 | Eaton
B165-101 Serial over Cat5/Cat6 ... Serial Adapter (F/F) is designed for connecting terminals, serial printers, modems, POS and other serial devices to your network via twisted-pair Cat5e/6 cabling....
Find elsewhere
Top answer
1 of 3
6

Those plugs are most likely (hard to tell from a picture) Cisco console cable plugs. They convert a DB-9 serial interface to a RJ45 receptacle , but NOT for use with a regular network cable. (They also exist in a DB-25 version.)
They are intended to use with a Cisco console cable (that has a RJ45 plug on 1 end and a DB-9 on the other) or a roll-over cable (RJ45 plug on both ends, but different pin-out than a network cable).

A Cisco console cable + a plug like yours connected to the other end make together a serial 3-wire null-modem cable.
A roll-over cable with 2 of these plugs (on each end) also makes a 3-wire null-modem cable.

That may be all you need. Provided that your lab-device needs a 3-wire null-modem cable, which is the most common case.
But some require a straight cable and in some (rare) cases you need a 5-wire null-modem (or straight) cable.

As modern computers, especially laptops, typically don't have a DB-9 serial port anymore, you may also need a USB to serial converter plug.

For short: There are a lot of variables here. Without more details about the devices involved and the exact nature of your plugs I can't get any more specific.

2 of 3
3

As Tonny wrote, that adapter is most likely a Cisco RJ45-to-DB9 converter, which is a purely passive adapter. The RJ45 side is not Ethernet, it's just RS232 on a different type of connector (Cisco devices used to have console ports with an RJ45 connector rather than the more common DB9 or DB25 connectors).

If you have an RS232 port on your laptop, then you just need a cable. While this was extremely common a couple of decades ago, nowadays I believe it's quite rare to find a laptop with an RS232 port.

So what you need instead is more likely an RS232-to-USB (aka serial-to-USB) converter/adapter.

Once you have that, you should have a new character device for the serial port somewhere in /dev (details may vary, but probably some kind of /dev/tty-something).

If you just want to capture the data from the serial port to a file, you can just cat /dev/serial_port_device_name >filename.

If you need to change serial port settings you can use stty but beware that you must keep the port open while you do it, otherwise the settings will reverse to defaults right away.

If you want something more foolproof, you can probably write a short script using the language of your choice, or they may be additional tools to manage that.

Alternatively there are devices with serial ports and Ethernet connections (you would then usually use telnet or netcat to connect to the serial ports and capture the data), but these would be more expensive, and only useful if you need to capture data from a larger distance.

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Newegg
newegg.com › home › networking › networking accessories › network ethernet cables › hitoor
RJ45 to RS232, DB9 9-Pin Serial Port Male to RJ45 Cat5 Ethernet LAN Console 3.3Ft / 1M - Newegg.com
RJ45 to RS232, DB9 9-Pin Serial Port Male to RJ45 Cat5 Ethernet LAN Console 3.3Ft / 1M
RJ45 to RS232, DB9 9-Pin Serial Port Male to RJ45 Cat5 Ethernet LAN Console 3.3Ft / 1M
Price   $8.99
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PUSR
pusr.com › blog › Are-RJ45-and-RS232-the-Same
Are RJ45 and RS232 the Same?-PUSR IOT
March 23, 2024 - RJ45 connectors are typically found on the ends of Ethernet cables and are used to plug into corresponding ports on network devices such as routers, switches, and computers. The RJ45 connector features eight pins arranged in a specific pattern, allowing for high-speed data transmission over long distances. RS232, on the other hand, is a serial communication standard that was developed in the 1960s.
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Cable Tester
cable-tester.com › home › pin out › rj45 rs232 console cable pin out
RJ45 RS232 Console Cable Pin Out
July 1, 2023 - One end is connected to the server with RJ45 connector (8P8C, 8 pins), and the other end is to a computer with a D-Sub connector (female 9 pins, often known as d-sub09 connector)
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Walmart
walmart.com › electrónica
Rs232 Ethernet
Compra Rs232 Ethernet en Walmart.com. Ahorra dinero. Vive mejor
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Reddit
reddit.com › r/networking › serial console over rj45 ethernet-patchpanels / rs232-ethernet-pinout?
r/networking on Reddit: Serial Console over RJ45 Ethernet-Patchpanels / RS232-Ethernet-Pinout?
July 5, 2021 -

Hello Guys,

we recently purchased an Avocent ACS8000 terminal server/console server for an OOBM for one of our customers, to have remote connections to local devices serial console ports. (mainly Cisco switches)

http://42u.com/pdf/Manual_Avocent-ACS-8000_userguide_501a.pdf

We also have to reach switches in a different fire compartment. Therefor we have to use standard Ethernet patchpanels. So now we are wondering how to cable it up!?

The Avocent terminal server has RJ45 ports with RS232 pinout.

The Cisco switches also have RJ45console ports, which are supposed to be rollover?

Page 5: https://www.cisco.com/c/en/us/td/docs/security/asa/hw/maintenance/5585guide/5585Xhw/pinouts.pdf

So now I am wondering, do we just use rollover cables?

[Cisco Console Port] - [rollover cable] - [RS232 port on Avocent terminal server]

[Cisco Console Port] - [rollover cable] - [Ethernet patchpanel] - [Ethernet cable] - [RS232 port on Avocent terminal server]

Or do I use the included Cisco RJ45-DB9 console cable (which is supposed to be doing a rollover already) on the switches and then a DB9(male)-RJ45 adapter.

[Cisco Console Port] - [Cisco console adapter RJ45-DB9] - [DB9-RJ45 adapter] - [Ethernet cable] - [RS232 port on Avocent terminal server]

[Cisco Console Port] - [Cisco console adapter RJ45-DB9] - [DB9-RJ45 adapter] - [Ethernet cable] - [Ethernet patchpanel] - [Ethernet cable] - [RS232 port on Avocent terminal server]

I am sure, I am not the first with this question, so there has to be an answer for that somewhere out there, so I hope someone can me poke into the right direction.

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Juniper Networks
juniper.net › documentation › us › en › hardware › mx2020 › srx4600 › topics › concept › port-rj45-db9-adapter-pinout.html
RJ-45 to DB-9 Serial Port Adapter Pinout Information | Juniper Networks
The console port on a Juniper Networks device is an RS-232 serial interface that uses an RJ-45 connector to connect to a management device such as a laptop or a desktop PC. If your laptop or desktop PC does not have a DB-9 plug connector pin and you want to connect your laptop or desktop PC ...
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eBay
ebay.com › electronics › computers/tablets & networking › computer cables & connectors › networking cables & adapters › ethernet cables (rj-45/8p8c)
Serial RS232 DB9 To RJ45 Adapter Cable POS Terminal Printers Console Serial Port | eBay
Serial RS232 DB9 To RJ45 Adapter Cable POS Terminal Printers Console Serial Port
Serial RS232 DB9 To RJ45 Adapter Cable POS Terminal Printers Console Serial PortSerial RS232 DB9 To RJ45 Adapter Cable POS Terminal Printers Console Serial Port
Price   $11.00
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Digi International
digi.com › support › knowledge-base › digi-connect-it-4-mini-and-digi-connect-it-16-48-r
Digi Connect IT 4/Mini & Digi Connect IT 16/48 - RJ45 RS232 Serial Pinout Differences | Digi International
Select your product for firmware, drivers, software, knowledge base articles and manuals · Digi Connect IT 16 & Digi Connect IT 48 use the same 8-wire RJ45 RS232 pinout
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US Converters
usconverters.com › downloads › support › db9_rj45_assembeling_guide.pdf pdf
www.usconverters.com Making a DB to RJ45 adapter.
The standard formerly known as RS-232 or RS232 became EIA-232 then TIA-232. Most of the world still ... RS-232D or EIA-561 defines the pin assignments for using RS-232 with RJ45 connectors. For an RJ45 male connector, the one you’ll find at both ends of a Cat6 cable, pin 1 is the left most pin
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DIY Solar Forum
diysolarforum.com › general discussion › diy solar general discussion
Solar Assistant Communication cable RS232 (RJ45) | DIY Solar Power Forum
August 3, 2023 - I ended up just having to bite the bullet and buy the cable from either Watts247 or SolarAssistant. If you have the programming cable that came with the inverter, you should be able to use that with the proper DB9 to USB cable. Click to expand...