Notice that as you progress through the modes on the Cisco IOS, more and more commands become available.

The Challenges

Sending data effectively through the network is a challenge for network designers and administrators regardless of the LAN topology. The first data−processing environments consisted mostly of time−sharing networks that used mainframes and attached terminals. Communications between devices were proprietary and dependent on your equipment vendor. Both IBM’s System Network Architecture (SNA) and Digital’s network architecture implemented such environments.

In today’s networks, high−speed LANs and switched internetworks are universally used, owing largely to the fact that they operate at very high speeds and support such high−bandwidth applications as voice and video conferencing. Internetworking evolved as a solution to three key problems: isolated LANs, duplication of resources, and a lack of network management.

Implementing a functional internetwork is no simple task. You will face many challenges, especially in the areas of connectivity, reliability, network management, and flexibility. Each area is important in establishing an efficient and effective internetwork. The challenge when connecting various systems is to support communication between disparate technologies. Different sites, for example, may use different types of media, or they may operate at varying speeds.

Reliable service is an essential consideration and must be maintained in any internetwork. The entire organization sometimes depends on consistent, reliable access to network resources to function and to prosper. Network management must provide centralized support and troubleshooting capabilities. Configuration, security, performance, and other issues must be adequately addressed for the internetwork to function smoothly. Flexibility, the final concern, is necessary for network expansion and new applications and services, among other factors.

Today’s Trend

In today’s networks, the trend is to replace hubs and bridges with switches. This approach reduces the number of routers connecting the LAN segments while speeding the flow of data in the network. A smart network administrator uses switches to inexpensively increase network bandwidth and ease network administration.

A switch is a low−cost solution to provide more bandwidth, reduce collisions, filter traffic, and contain broadcasts. But, switches don’t solve all network routing problems. Routers provide a means of connecting

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multiple physical topologies, restricting broadcasts, and providing network security. Using switches and routers together, you can integrate large networks and provide a high level of performance without sacrificing the benefits of either technology.

Entering and Exiting Privileged EXEC Mode

After the switch has gone through the power on self test (POST), it will come to a User EXEC mode prompt with the hostname and an angle bracket as shown here, assuming no password has been configured:

Switch>

To enter Privileged EXEC mode, use the following command. You will notice that the prompt changes to indicate that you are in Privileged EXEC mode:

Switch>enable

Switch>(enable)

To exit Privileged Exec mode and return to User EXEC mode, use the disable command.

Entering and Exiting Global Configuration Mode

From Privileged EXEC mode, you can enter Global Configuration mode by using the following command. Notice again that the prompt changes for each successive mode:

Switch>(enable)configure terminal

Switch(config)#

To exit Global Configuration mode and return to Privileged Exec mode, you can use the end or exit command, or press Ctrl+Z.

Entering and Exiting Interface Configuration Mode

To configure an interface, you must enter Interface Configuration mode. From the Global Configuration mode command prompt, use the following command. You must specify the interface and number; this example configures the Ethernet 0 port:

Switch(config)#interface e0

Switch(config−if)#

To exit to Global Configuration mode, use the exit command or press Ctrl+Z.

Entering and Exiting Subinterface Configuration Mode

To configure a subinterface on an interface, use the following command. You must specify the interface and the subinterface, separated by a decimal; the second number identifies the subinterface:

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Switch(config−if)#interface e0.1

Switch(config−subif)#

Tip You can abbreviate any command as much as you want, as long as it remains unique (no other command exists that matches your abbreviation). For instance, the command interface e0.1 can be abbreviated as int e0.1.

To exit to Global Configuration mode, use the exit command or press Ctrl+Z.

Tip Entering a question mark (?) in any mode will display the list of commands available for that particular mode. Typing any command followed by a question mark—such as clock ?—will list the arguments associated with that command. You can also type the first few letters of a command immediately followed by a question mark. This will list all the commands starting with the entered letters.

Saving Configuration Changes

When you’re saving the configuration, the Set/Clear IOS−based switches are identical to the IOS−based CLI. The configuration modes allow you to make changes to the running configuration. In order to save these changes, you must save the configuration.

There are two types of configuration files: Startup configuration files are used during system startup to configure the software, and running configuration files contain the current configuration of the software. The two configuration files do not always agree.

To make a change to the running configuration file:

1.Issue the command configure terminal.

2.Make any necessary changes.

3.When you are done, copy the running configuration to the startup configuration.

In the following example, the hostname is being changed and then saved to the start−up configuration:

Switch> enable

Switch# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# hostname BBSwitch

BBSwitch (config) end

BBSwitch# copy running−config startup−config

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