Accessing the CLI

On real network equipment, the starting point will always be to make a connection to the CLI.

The simplest way to do this is to use a console cable. In previous notes we have discussed serial data communications and the RS232 protocol. Most manufacturers supply a console port on standard equipment, and this is what we connect to initially. In some cases, this will be a standard DB9 connector, but in many cases, this will terminate in a proprietary RJ 45 connector. This was originally a Cisco standard, and every practising engineer carries a blue Cisco terminal cable. Interestingly, many other manufacturers adopted the same wiring; I can connect to most of my Hewlett-Packard switches using the same cable.

The first step may be to create a management IP address with which to do further configuration work. A serial connection is not the most flexible and scalable way of doing configuration. If a switch is isolated and sitting on the bench, we can use telnet to do initial configurations. However, telnet is an unsecured protocol should not be used in any connected environment. As quickly as reasonably possible, we configure SSH, complex encrypted passwords, and we perform basic security tasks before connecting the switch to a network. Most network engineers I know use Putty as a console. This gives access to serial ports, telnet and SSH through a simple interface.

Better again, we create an ideal configuration and test it, and then we deploy that to any new switch before it connects to a network.

Modern laptops do not have conventional RS 232 ports. Any practising network engineer has a USB to RS 232 converter in the laptop case. It is our most used peripheral! Serial ports originally were built into the hardware of PCs and had specific assignments; COM1, 2, 3, 4. On a modern system, the USB connection can be assigned to a wide range of numbers. To check to see which COM port has been assigned to your USB adapter, open the device management window (devmgmt.msc) in Windows and check under ports.