Every Cisco engine…rock star in the world should have a rollover cable or two stashed away in their bag/car/pocket just in case.  The rollover serial cable is the hallmark of access to a Cisco device.  The console port is the last resort for configuration when all else has gone wrong.  It is the first thing you should plug into when you boot up a router for the first time and the best way to get info you couldn’t otherwise find.  However, the days of the serial cable are quickly becoming numbered.

It wasn’t all that long ago that every PC manufactured included a 9-pin serial connection.  These ports were handy for all kinds of devices, including printers and modems.  However, with the introduction of Universal Serial Bus (USB) connections, the usefulness of the serial (and parallel) ports has been waning quickly.  By utilizing a higher speed connection that more tightly integrates into the system, the need to configure devices with DIP switches and play COM port roulette have long since passed.  As it is with any transition though, there have been some holdouts in the movement to retire serial ports.  While some of these are understandable due to outdated single-purpose technology, others have never made any sense to me, like the Cisco rollover console cable.  Surely there must be a better way to connect to the serial port of a device than with an outdated technology holdover from the 80s?  I myself am a victim of this kind of thinking, having used an IBM T30 Thinkpad well past its useful life simply because it had an integrated serial port and my replacement laptop wouldn’t.

When Cisco developed the new ISR G2 line of routers, someone in the console access department finally decided to wake up and get with the 2000’s.  Thanks to their efforts, the Cisco routers and switches manufactured today have started including a new console access option:

In the picture above, you can see the familiar RJ-45 console port to the right and the newer USB console port to the left, indicated with the USB icon.  This new port allows those of us that have spent most of our lives using the flat blue rollover serial cables to add a new, exciting cable to our bag, the USB A-to-mini cable.

The new USB port allows the user to access the router’s console with a newer cable instead of relying on the standby rollover cable.  However, you need to take a few steps first.  You have to head out to the Cisco Connections Online (CCO) download page and pull the driver for your particular operating system if you’re running on Windows.  Make sure you specify 32-bit or 64-bit, since this driver will be masquerading as a COM port on your system.  You don’t want to waste time downloading a driver that won’t work.  Once you’ve installed the driver, you can plug in your USB connection to any USB port and then to the router.  It will look like an additional COM port on your system, probably with a high number like COM6 or COM7, so make sure you’ve got a terminal emulator that allows you to choose your COM port.  I tend to use TeraTerm for this very reason, but your terminal program of choice should do nicely.  For those of you in the audience with Macbooks, you don’t need to download any drivers at all.  Seems like OS X already has the right driver built in, so just plug and and get cranking.  As a quick aside, Cisco will attempt to sell you a $30 USB console cable when you order the router. JUST. SAY. NO.  This is a regular USB A-to-Mini cable that can be purchased at Walmart for about $10.  You can even use the USB cable that came with your digital camera or Blackberry or old Motorola RAZR.

Once you get attached to the USB console port, you’ll find that it works pretty much the same as the RJ-45 port that you’ve become attached to over the years.  You can also plug in a regular old serial cable into the RJ-45 port if you need a second connection.  The RJ-45 console port will mirror what’s going on with the USB console port.  However, since their both Console 0, only one of them will have preference on the input.  In this case, that’s the USB port.  So if you have a terminal access server plugged in for reverse telnet connections and someone comes in and attaches a USB connector, you can watch what’s going on but you can’t do anything about it.  You can specify a timeout value if you’d like so you can force a logout after inactivity.  You can do that with the following command:

Router(config)# line con 0
Router(config-line)#usb-inactivity-timeout <value in minutes>

Note that this command doesn’t work on the 2900 series ISR G2 routers for some strange reason.  Oh well, feature request down the road.  For those of you out there that don’t feel comfortable with the idea of having just anyone off the street walking up and consoling into your router via USB, you can always disable the USB console port in favor of the RJ-45 connection as follows:

Router(config)# line con 0
Router(config-line)# media-type rj45

Bingo.  USB port locked out.  Now only those people in possession of a serial-to-USB adapter or a Redpark iOS Console Cable will have access.

Tom’s Take

I have three rollover cables in my various laptop bags.  I keep two for emergencies and one in case someone doesn’t have theirs.  I passed out console cables to all my engineers and technicians once and told them the next time I asked them for their console cable, they’d better present this one to me.  A console cable is an indispensable tool for anyone that works on Cisco equipment.  Having the USB option is always welcome since I no longer have to fumble for my USB-to-serial adapter or worry that the dodgy drivers are going to bluescreen my Windows 7 64-bit laptop over and over again.  Still, there is a lot of Cisco equipment out there with the older RJ-45 cable setup as the only console option.   So you can’t just throw out the old rollover serial cables just yet.  Better to throw a USB cable in your bag for those glorious days where you get to access a newer device.  Then you can await the day when you can bury your rollover cable alongside Beethoven.