Router Overview - The Console Port

Every Cisco router has a console port on its back. It is there to provide a way to hookup a terminal to the router in order to work on it. The console port (sometimes called the management port) is used by administrators to log into a router directly — that is, without a network connection. The console must be used to install routers onto networks because, of course, at that point there is no network connection to work through.

Long term,the console’s role is to be there as a contingency in case of emergency. When a router is completely down — in other words, when it is no longer able to process network packets — it cannot be accessed via the network. If the router is up and processing packets,but the network segment through which the technician must access it is down, going over a network to fix the router is not an option. This is when the console port provides a sure way to log into the router to fix things. The drawback, of course, is that someone must be in the same physical location as the router in order to connect to it.

A stand-alone CRT, PC, or workstation can be used as a console. Console terminals must run a character-based user interface. They cannot run a graphical user interface (GUI) such as Microsoft Windows, Mac OS, or X-Windows. In order to use a PC or workstation as a console, you must use terminal emulator software. For example, one of the best-known terminal emulators is HyperTerminal from Hilgraeve, Inc., which ships with all versions of Windows. Start up HyperTerminal (or one of the many other terminal emulator products) and log into the router from there.

Console ports in Cisco routers use a variety of connector types (25-pin, RJ-45, 9-pin, and so on), but all provide a single terminal connection. A word of warning: make sure you have the proper cable before trying to hook up a console terminal to work on a router. Many a network administrator has spent a half hour fiddling with cables to finally find one that could connect to a router just to do 15 minutes of productive work.

NOTE: Console ports on Cisco devices are usually labeled “Console”—but not always. On some products, console ports are labeled “Admin,” and on others they are labeled “Management.” Don’t be confused by this; they are all console ports.

Most Cisco routers have a second port on the back called the auxiliary port (usually called the AUX port,for short). Like the console port, the AUX port makes possible a direct, nonnetwork connection to the router.

How does the AUX port differ from the console port? The AUX port uses a connector type that modems can plug into (console ports have connectors designed for terminal cables). If a router in a faraway data closet goes down, the network administrator asks somebody in the area to go to the router and plug in a modem so it can be serviced remotely. In more critical configurations, a modem is often left permanently connected to a router’s AUX port. Either way, the AUX port affords console-like access when it isn’t practical to send a technician to the site to work on a router through a local console. Figure 4-6 shows the console and AUX ports on the back of a Cisco 4500 router.

NOTE: Cisco’s smaller routers do not have AUX ports, only console ports. These devices support remote management logins by connecting a modem to the router using an auxiliary/console cable kit.

This chapter is from Cisco: A Beginner's Guide, by Velte and Velte (McGraw-Hill/Osborne, 2004, ISBN: 0072256354). Check it out at your favorite bookstore today.  Buy this book now.

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