When connecting to a Catalyst OS
"set command" based switch (such as the Catalyst 4000 and
6000), you are presented with a password prompt at the initial
login. The default password for
a Catalyst 4000 is pressing the ENTER key. Assuming you enter
the correct password, you enter the switch's NORMAL mode. Normal mode
equates to a router's User EXEC mode, allowing you to view most switch
parameters, but not permitting any configuration changes. To make
changes, you must enter PRIVILEGED mode.
The privileged mode functionally equates to the router PRIVILEGED
EXEC mode. In the privileged mode, you can view configuration files
like you can with a router; however, in the switch privileged mode
you can make configuration changes, unlike a router where you have
to enter global configuration mode. With both a CLI-based switch and
a set command-based switch, you enter the switch privileged mode
with the enable
command. With a CLI-based switch, the command prompt turns to
Switch#, where a pound sign (#) rather than a greater than sign
(>) follows the switch name. With a set command-based switch, the
command prompt turns to
Console> (enable). The switch then prompts
you for a password to enter privileged mode.
Remember, you can access the switch
CLI through the console interface or through a Telnet session. Like
in a router, commands in a switch are additive. This means that
adding configuration statements to an existing file will not
completely overwrite the existing configuration.
A foolproof way of ensuring that a
new configuration completely overwrites an existing configuration is
to enter the clear config
all command, as shown in
Figure .
If you clear the configuration while accessing the switch via
Telnet, you will not see the output in the Figure. You see this
only when directly attached to the console. This CLI command returns
the switch Supervisor module to its default configuration where all
ports belong to virtual LAN (VLAN) 1, there is no Virtual Trunking
Protocol (VTP) domain (explained in Chapter 4), and all
Spanning-Tree parameters go back to their default values. It is
important to note also that entering this command also clears the
console IP address. You can clear the configuration with any of the
access methods, but if you do so while telnetting to the Catalyst
Switch, you lose your connection because the switch no longer has an IP address.
On a 2900 switch, the
erase startup-config
command erases the configuration that is stored in
NVRAM. On a 2900 switch, this does not erase the VLAN information. In order to erase the VLAN information, use the
del flash:vlan.dat command.

The clear
config all command
affects only modules that are directly configured from the Supervisor
module. To clear the configurations on the router modules, you need
to access the modules with the session
module_number command. This
command performs the equivalent of an internal Telnet to the module.
To display which slot
the router module is in, use the show module command. The router modules on a
switch use Cisco IOS commands to change, save, and clear
configurations.
Unlike routers, the set command-based
switch immediately
stores commands in nonvolatile random-access memory (NVRAM) and does
not require you to perform a copy
run start command. Any command typed
into a switch is immediately stored and remembered, even through a
power cycle. This presents a challenge when attempting to reverse a
series of commands. On a router, you can reverse a series of
commands with reload, as long as you didn't write the running
configuration into NVRAM.
Before making serious changes to a
set command-based switch, copy the configuration to a backup text file or to a Trivial
File Transfer Protocol (TFTP) server (described later in this
section). Then if you do not like the
changes you made, you can use the clear
config all command to clear
the switch. Then load the previously saved configuration file.
On the other hand, if you are working
with a Cisco IOS command-based switch, the switch behaves much
more like a router. In the switch user exec mode, you cannot make
changes. Use the enable
command to access privileged mode where you will be able
to view extensive configuration parameters. However,
you still cannot configure the switch. To configure the
switch, you must enter configuration mode by using the configure
command. This command puts the switch in global
configuration mode, where you are able to configure the
switch.
Configuring the switch through the console and through
Telnet allows you to enter commands in real time, but only one at a
time. Unlike set command-based switches, the Cisco IOS command-based
switch does not immediately store commands in NVRAM, and does
require you to perform a copy
run start like a router. This
greatly reduces the challenge when attempting to reverse a series of
commands. As with a router, you can reverse a series of commands
with a reload (provided that you didn't write the running configuration
into NVRAM).
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