Cisco IOS Access Modes and Essential Commands

Cisco IOS uses command modes to separate observation from configuration. The prompt is a safety signal: check it before entering a command.

Access and modes

Use the console for first access. SSH is preferred for remote administration; Telnet sends credentials without encryption and should be limited to an isolated lab, if used at all.

Switch> enable
Switch# configure terminal
Switch(config)# interface gigabitEthernet 0/1
Switch(config-if)# exit
Switch(config)# end
Switch# disable
Switch>

> is user EXEC, # is privileged EXEC, (config)# is global configuration, and (config-if)# is interface configuration. end returns to privileged EXEC; Ctrl-Z usually does the same.

Inspect before changing

show version
show running-config
show startup-config
show interfaces status
show ip interface brief
show cdp neighbors detail

Use show running-config for active configuration and show startup-config for the configuration used after reboot. They may differ.

Save and recover

copy running-config startup-config
reload

Do not reload just to test a change. Save only after verification. If a remote change may disconnect you, use a console or a scheduled rollback plan.

Built-in help

show ?
show ip ?
terminal length 0

The question mark and tab completion are safer than guessing IOS syntax.

Continue with Cisco IOS Device and Interface Configuration.