The first thing that you’ll notice when you pull a Cisco 2500 series router out of the box is obviously its physical elements. A Cisco 2501 includes not only Ethernet and serial ports, but also console and auxiliary ports. In this section we’ll look at the purpose of each, their physical characteristics, and how devices are attached and cabled. The figure below outlines the location of the various ports on a Cisco 2501. Note that hardware ports are numbered nominally starting at 0. Therefore, on a system with only one Ethernet port, that port is referred to as Ethernet 0. On a Cisco 2501, the leftmost serial port is referred to as Serial 0, and the rightmost as Serial 1.
The port numbering arrangement for newer Cisco router models (well, newer than the old workhorse 2500s) is somewhat different, and you should be aware of it. For example, a Cisco 2600 router follows the convention interface slot/port when referring to an interface. Fixed interfaces (those not part of add-in modules) are generally referenced using slot 0. So, if you were attempting to access the first fixed Fast Ethernet port, it would be port FastEthernet 0/0. If the model had a second such port, it would be FastEthernet 0/1. By the same token, if you added a four-port serial module to your 2600 router, those ports would be known as Serial 1/0 through 1/3 respectively. On the CCNA exam, it is very important that you reference ports correctly. If you’re not sure of the port numbering method used on a particular model (especially during router simulation questions) you can always use the show interfaces command to confirm. This command and many others will be explained in detail in Chapter 7.