Exam Essentials

Understand how the set-based and IOS-based command lines are different. Set-based commands belong to a legacy operating system purchased by Cisco when they bought the original switching company, so they bear no resemblance to the Cisco IOS at all. The only three commands in use-set, clear, and show-are used for all purposes. Interface/port configurations, passwords, and all VLAN and trunking options are changed from the defaults using set commands. Configurations are removed using clear commands, and show commands are used to display configurations, interfaces, memory, and so on.

Newer switches, such as the 3550 and 2950, use the familiar Cisco router IOS command set. Password, hostname, and other administrative commands are the same as for the router, and the only real difference is that because this is a switch, the command options may be reduced, omitting router specifics such as routing, on the 2950 switches. The 3550 switches, which support native routing, and the 4000 and 6500 series running the native IOS upgrade, actually support routing as well, and so have a full set of IOS commands.

Understand physical network connectivity. Some cables are suitable for some tasks but not for others, and the characteristics of each cable help determine which tasks they should be used for. For instance, Ethernet cables can be straight through, as used with PCs to switch connections, or crossover, as used for switch-to-switch links. You need to know the characteristics and limitations of each type of cable.

Understand logical network connectivity. There are several issues to confront with connectivity at layers 1 and 2. We know that hubs operate at layer 1 and switches at layer 2, which immediately identifies some major differences. For instance, a switch allows for full-duplex connectivity, but a hub does not. Also, turning on auto-detection for speed forces duplex into auto-detect mode.