backward compatible to most of the equipment in use at the time. Although the standards bodies debated the merits of each of the camps, the marketplace decided for them. Fast Ethernet is the overwhelming winner, so much so that even HP sells Fast Ethernet on almost all its products.

Note In 1995, Cisco purchased both Kalpana and Grand Junction and incorporated their innovations into its hardware. These devices became the Catalyst line of Cisco products.

Gigabit Ethernet

In order to implement Gigabit Ethernet (GE), the CSMA/CD method was changed slightly to maintain a 200−meter collision diameter at gigabit−per−second data rates. This slight modification prevented Ethernet packets from completing transmission before the transmitting station sensed a collision, which would violate the CSMA/CD rule.

GE maintains a packet length of 64 bytes, but provides additional modifications to the Ethernet specification. The minimum CSMA/CD carrier time and the Ethernet slot time have been extended from 64 bytes to 512 bytes. Also, packets smaller than 512 bytes have an extra carrier extension added to them. These changes, which can impact the performance of small packets, have been offset by implementing a feature called packet bursting, which allows servers, switches, and other devices to deliver bursts of small packets in order to utilize the available bandwidth.

Because it follows the same form, fit, and function as its 10− and 100Mbps predecessors, GE can be integrated seamlessly into existing Ethernet and Fast Ethernet networks using LAN switches or routers to adapt between the different physical line speeds. Because GE is Ethernet, only faster, network managers will find the migration from Fast Ethernet to Gigabit Ethernet to be as smooth as the migration from Ethernet to Fast Ethernet.

Avoiding Fork−Lift Upgrades

Although dedicated switch connections provide the maximum benefits for network users, you don’t want to get stuck with fork−lift upgrades. In a fork−lift upgrade, you pay more to upgrade your computer or networking equipment than it would cost to buy the equipment already installed. The vendor knows that you are not going to buy all new equipment, so the vendor sells you the upgrade at an enormous price. In order to exchange it for the bigger, better, faster equipment It may sometimes be necessary to support legacy equipment.

Fortunately for Ethernet switches you can provide connectivity in a number of ways. You can attach shared hubs to any port on the switch in the same manner that you connect end stations. Doing so makes for a larger collision domain, but you avoid paying the high costs of upgrades.

Typically, your goal would be to migrate toward single−station segments as bandwidth demands increase. This migration will provide you with the increased bandwidth you need without wholesale replacement of existing equipment or cabling.

In this lower cost setup, a backbone switch is created in which each port is attached to the now−larger collision domain or segment. This switch replaces existing connections to routers or bridges and provides communication between each of the shared segments.

The Cisco IOS

The Cisco Internetwork Operating System (IOS) is the kernel of Cisco routers and switches. Not all Cisco

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devices run the same IOS. Some use a graphical interface, some use a Set/Clear command−line interface, and some use a Cisco Command Line Interface (CLI). Cisco has acquired more devices than they have designed and built themselves. Therefore, Cisco has adapted the operating systems designed for each device they have acquired to use the protocols and standards of the company. Almost all Cisco routers run the same IOS, but only about half of the switches currently run the Cisco CLI IOS.

Knowing what configuration mode you are in and how to enter each configuration mode on the Cisco CLI is important. Recognizing what each mode configures will aid you in using the proper configuration mode. The Set/Clear command−based IOS is similar in modes, but uses the enable, set, show, and clear commands (covered in the next chapter).

Connecting to the Switch

You can connect to a Cisco switch to configure the switch, verify the configuration, or check statistics. Although there are different ways of connecting to a Cisco switch, typically you would connect to its console port.

In lower−end Cisco switches, the console port is usually an RJ−45 connection on the back of the switch. On a higher−end switch, you may find console ports on the line cards such as a Supervisor Engine. By default there is no password set on the console port.

Another way to connect to a Cisco switch or router is through an auxiliary port. This is basically the same as connecting through a console port, but it allows you to connect remotely by using a modem. This means you can dial up a remote switch and perform configuration changes, verify the configuration, or check statistics.

A third way to connect to a Cisco switch is through the program Telnet. Telnet is a program that emulates a dumb terminal. You can use Telnet to connect to any active port on the switch, such as an Ethernet or serial port.

Cisco also allows you to configure the switch by using Switch Manager, which is a way of configuring your switch through a Web browser using HTTP. This method creates a graphical interface for configuring your switch. The Switch Manager allows you to perform most of the same configurations as you can with the CLI.

Powering Up the Switch

When you first power up a Cisco switch, it runs the power on self test (POST), which runs diagnostics on the internal workings of the switch. If the switch passes this test, it will look for and load the Cisco IOS from Flash memory if a file is present. Flash memory is read−only memory kept on an EEPROM (a silicon chip inside of the switch). The IOS then loads the configuration contained in nonvolatile RAM (NVRAM). NVRAM is similar to random access memory (RAM) but is not lost when the power is cycled on the switch. This loads the configuration of the Cisco IOS and the Cisco user interface becomes available.

The Cisco IOS user interface is divided into several different modes. The commands available to you in each mode determine the mode you are in. When you start a session on the switch, you begin in User EXEC mode, often called EXEC mode. Only a limited subset of the commands is available in EXEC mode. In order to have access to all commands, you must enter Privileged EXEC mode. From Privileged EXEC mode, you can enter any EXEC command or enter Global Configuration mode, which offers even more command options. From global configuration mode you can also enter into any interface configuration mode to configure an interface (port) or a subinterface.

Subinterfaces

Subinterfaces allow you to create virtual interfaces within an interface or port on a switch. When entering an interface number with a decimal subinterface number, the prompt changes to (config−subif)#. Let’s look at an example:

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Router(config)#interface e0/0.? <0−4294967295> Ethernet interface number Router(config)#interface e0/0.1 Router(config−subif)#

Let’s take a look at the commands available in the User EXEC mode of a Cisco Catalyst 1912 EN switch:

terminal Set terminal line parameters SeansSwitch>

The following commands are available in Privileged EXEC mode:

Finally, the following commands are available in Global Configuration mode:

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