What Is a Cisco Console Cable?

What is a Cisco console cable?

Posted by: David Davis
Networking, Cisco, CCNA

Say that you take a new Cisco router, switch, or firewall out of the box and hook it up. Does it work? No. It isn’t like a Linksys or Netgear router. It has no DHCP or anything like that. It has to be configured first.

How do you configure it? You have to connect to the console port, like this console port on a Cisco 1800 series router:

But what to connect to it? No, don’t use an Ethernet cable - it won’t work. This is a SERIAL port that needs to go to the serial/COM port on your PC or laptop (if you still have one). What what you need is a ROLLED cable. Here is what it looks like:

Cisco also has a good picture of one, below….

However, how are you going to get that rolled cable connected to your PC? Don’t plug it into the Ethernet port! Remember, it is a Serial Cable. You need to connect it to the 9 PIN serial port on your PC (hopefully you have one but I will tell you what to do if you don’t in a minute. To connect it, you need to convert the RJ45 end to Serial with an adaptor, like this:

Many times, these came with routers or were sold in a package alone with the rolled cable, like this:

Today, the DB9 to RJ45 converter is coming molded to the console cable, like this:

Hi David

Just a quick point. Above you mention that you connect the DB9 adapter to the COM port on your PC or laptop and you mentioned that you would tell people how to get around the issue of their laptop not having a COM port later, but you never did. Now I am quite sure that the majority if not all the people reading this will be aware of the fact that you can get a USB to DB9 adapter cable, but just for completeness and for anybody new to IT networking I thought I would mention it.

Also, a handy bit on information for if you ever find yourself in the position of having access to one of the DB9-RJ45 adapters shown above but no rollover cable.

The cable layout of these adapters is as follows
Pin 1 — Blue wire
Pin 2 — Orange wire
Pin 3 — Black wire
Pin 4 — Red wire
Pin 5 — Green wire
Pin 6 — Yellow wire
Pin 7 — Brown wire
Pin 8 — Grey/White wire

So if you wire the DB9-RJ45 adapter as follows you can use it with a CAT5 straight cable to gain console access to Cisco equipment. The adapter should have a female DB9 interface.

Blue cable to position 8
Orange cable to position 6
Black cable to position 2
Yellow cable to position 3
Brown cable to position 4
Grey/white cable to position 7
Red and green cables spliced together to position 5

To splice the red and green cables together, remove the small brass pin from one of the cables and bare a little of the wire.

Carefully remove a small amount of the outer plastic covering of the other cable to bare the wire.

Join the bare wires from each cable together and secure with insulation tape.