Content Overview A switch is a Layer 2
network device that acts as the concentration point for the
connection of workstations, servers, routers, hubs, and other
switches. A hub is an older type of concentration device which
also provides multiple ports. However, hubs are inferior to
switches because all devices connected to a hub reside in the
same bandwidth domain that produces collisions. Another
drawback to using hubs is that they only operate in half-duplex
mode. In half-duplex mode, the hubs can send or receive data at
any given time, but not both at the same time. Switches can
operate in full-duplex mode, which means they can send and
receive data simultaneously. Switches are multi-port bridges.
Switches are the current standard technology for Ethernet LANs
that utilize a star topology. A switch provides many dedicated,
point-to-point virtual circuits between connected networking
devices, so collisions are virtually impossible. Because of
their dominant role in modern networks, the ability to
understand and configure switches is essential for network
support. A new switch will have a preset configuration with
factory defaults. This configuration will rarely meet the needs
of a network administator. Switches can be configured and
managed from a command-line interface (CLI). Increasingly,
networking devices can also be configured and managed using a
web based interface and a browser. A network administrator must
be familiar with many tasks to be effective in managing a
network with switches. Some of these tasks are associated with
maintaining the switch and its Internetworking Operating System
(IOS). Others are associated with managing interfaces and
tables for optimal, reliable, and secure operation. Basic
switch configuration, upgrading the IOS, and performing
password recovery are essential network administrator skills.
Students completing this module should be able to:
- Identify the major components of a Catalyst switch
- Monitor switch activity and status using LED
indicators
- Examine the switch bootup output using
HyperTerminal
- Use the help features of the command
line interface
- List the major switch command modes
- Verify the default settings of a Catalyst
switch
- Set an IP address and default gateway for the
switch to allow connection and management over a network
- View the switch settings with a Web browser
- Set
interfaces for speed and duplex operation
- Examine and
manage the switch MAC address table
- Configure port
security
- Manage configuration files and IOS
images
- Perform password recovery on a switch
- Upgrade the IOS of a switch
Content
6.1 Starting the Switch 6.1.1
Physical startup of the Catalyst switch Switches are dedicated,
specialized computers, which contain a central processing unit
(CPU), random access memory (RAM), and an operating system. As
shown in Figure , switches usually have several ports for the
purpose of connecting hosts, as well as specialized ports for
the purpose of management. A switch can be managed by
connecting to the console port to view and make changes to the
configuration. Switches typically have no power switch to turn
them on and off. They simply connect or disconnect from a power
source. Several switches from the Cisco Catalyst 2950 series
are shown in Figure .
Content 6.1 Starting
the Switch 6.1.2 Switch LED indicators The
front panel of a switch has several lights to help monitor
system activity and performance. These lights are called
light-emitting diodes (LEDs). The front of the switch has the
following LEDs: - System LED
- Remote Power
Supply (RPS) LED
- Port Mode LED
- Port Status
LEDs
The System LED shows whether the system is
receiving power and functioning correctly. The RPS LED
indicates whether or not the remote power supply is in use. The
Mode LEDs indicate the current state of the Mode button. The
modes are used to determine how the Port Status LEDs are
interpreted. To select or change the port mode, press the Mode
button repeatedly until the Mode LEDs indicate the desired
mode. The Port Status LEDs have different meanings, depending
on the current value of the Mode LED.
Content
6.1 Starting the Switch 6.1.3 Verifying
port LEDs during switch POST Once the power cable is connected,
the switch initiates a series of tests called the power-on self
test (POST). POST runs automatically to verify that the switch
functions correctly. The System LED indicates the success or
failure of POST. If the System LED is off but the switch is
plugged in, then POST is running. If the System LED is green,
then POST was successful. If the System LED is amber, then POST
failed. POST failure is considered to be a fatal error.
Reliable operation of the switch should not be expected if POST
fails. The Port Status LEDs also change during switch POST. The
Port Status LEDs turn amber for about 30 seconds as the switch
discovers the network topology and searches for loops. If the
Port Status LEDs turn green, the switch has established a link
between the port and a target, such as a computer. If the Port
Status LEDs turn off, the switch has determined that nothing is
plugged into the port.
Content 6.1 Starting
the Switch 6.1.4 Viewing initial bootup output from the
switch In order to configure or check the status of a switch,
connect a computer to the switch in order to establish a
communication session. Use a rollover cable to connect the
console port on the back of the switch to a COM port on the
back of the computer. Start HyperTerminal on the computer. A
dialog window will be displayed. The connection must first be
named when initially configuring the HyperTerminal
communication with the switch. Select the COM port to which the
switch is connected using the pull-down menu, and click the OK
button. A second dialog window will be displayed. Set up the
parameters as shown, and click the OK button. Plug the switch
into a wall outlet. The initial bootup output from the switch
should be displayed on the HyperTerminal screen. This output
shows information about the switch, details about POST status,
and data about the switch hardware. After the switch has booted
and completed POST, prompts for the System Configuration dialog
are presented. The switch may be configured manually with or
without the assistance of the System Configuration dialog. The
System Configuration dialog on the switch is simpler than that
on a router.
Content 6.1 Starting the
Switch 6.1.5 Examining help in the switch CLI The
command-line interface (CLI) for Cisco switches is very similar
to the CLI for Cisco routers. The help command is issued
by entering a question mark (?). When this command is
entered at the system prompt, a list of commands available for
the current command mode is displayed. The help command
is very flexible. To obtain a list of commands that begin with
a particular character sequence, enter those characters
followed immediately by the question mark (?). Do not
enter a space before the question mark. This form of help is
called word help, because it completes a word. To list keywords
or arguments that are associated with a particular command,
enter one or more words associated with the command, followed
by a space and then a question mark (?). This form of
help is called command syntax help, because it provides
applicable keywords or arguments based on a partial command.
Interactive Media Activity Fill in the Blanks: Switches
and Collision Domain After completing this activity, the
student will be able to identify the role of a switch in
preventing collisions and reducing collision domains.
Content 6.1 Starting the Switch 6.1.6
Switch command modes Switches have several command modes. The
default mode is User EXEC mode. The User EXEC mode is
recognized by its prompt, which ends in a greater-than
character (>). The commands available in User EXEC