Section 4: The Cisco IOS Operating System

'Router#' is in Cisco IOS [...] mode.

Privileged EXEC

'Router(config)#' is in [...] mode.

Global Configuration

Commands that are entered in the running configuration do not get saved permanently until you explicitly copy them from the [...] to the [...].

running configuration, startup configuration

The [...] is loaded into RAM from the startup config when the device boots up.

running configuration

The Cisco operating system used on the majority of Cisco enterprise grade network devices.

IOS (Internetworking Operating System)

The running configuration is stored in the [...].

RAM

The [...] command is entered to access the Global Configuration mode from the Privileged EXEC mode.

configure terminal

The [...] is the configuration that will go into effect when the router is next started or rebooted.

startup configuration

This command makes the running configuration persistent across reboot.

copy running-config startup-config or copy run start

What Cisco IOS command line mode is 'Router(config-if)#' in?

Interface Configuration mode 

What Cisco IOS command line mode is 'Router>' in?

User EXEC mode

Where is the IOS operating system image stored?

Flash

Where is the startup configuration stored?

NVRAM

What protocol is used for secure remote CLI access to Cisco devices, and why is it preferred over the alternative?

SSH (Secure Shell) — preferred over Telnet because SSH encrypts commands/credentials, while Telnet sends them unencrypted.

What does AAA stand for, and what is its purpose?

Authentication, Authorization, and Accounting — a centralized server that manages usernames/passwords across many devices, rather than configuring credentials separately on each device.

What is the main advantage of Out-of-Band Management over In-Band Management?

It provides a backup path to reach a device if the Production Network has a problem, and is generally more secure since it's isolated from normal user traffic.

What type of cable is used to make a console connection, and what connectors does it use?

A console (rollover) cable — DB9 serial connector on one end (to the PC) and RJ45 connector on the other (to the device's console port).

Is a console cable an Ethernet cable?

No — despite the RJ45 connector, it does not use Ethernet and does not require IP addressing.

What command takes you from User EXEC mode to Privileged EXEC mode?

enable

How can you tell whether you're in User EXEC mode or Privileged EXEC mode just by looking at the command prompt?

User EXEC mode ends with a > symbol; Privileged EXEC mode ends with a # symbol (both preceded by the hostname).

What does the "Invalid input detected" error typically indicate, and how does the CLI help you identify the issue?

Usually a typo in the command; the CLI marks the exact location of the error with a caret (^).

What does the "Incomplete command" error mean?

The command entered requires additional keywords/parameters to be valid — it's missing required input.

What is the key functional difference between a show command and a debug command?

show displays point-in-time (static) information about the current state; debug displays output in real time as events occur.

What key brings back the previous command entered at the CLI?

Up arrow

How can you run a show command from a configuration level (like global config) without first exiting back to Privileged EXEC mode?

Prefix the command with do (e.g., do show ip interface brief).

What command is used to enter Interface Configuration mode, and what does the resulting prompt look like?

interface <interface name> (e.g., interface fastEthernet 0/0) — the prompt changes to show (config-if).

What command (or shortcut) returns you directly to Privileged EXEC mode from any lower level, in a single step?

end, or Ctrl+C

What command shows the status (up/down) and IP address of all interfaces on a router?

show ip interface brief

What does show run | begin <keyword> do?

Displays the running configuration starting from the first line where the keyword appears.

What does show run | include <keyword> do?

Displays only the lines in the running configuration that contain the specified keyword.

What does show run | exclude <keyword> do?

Displays all lines in the running configuration except those containing the specified keyword.

What does show run | section <keyword> do?

Displays the full configuration block for the matching section (e.g., show run | section bgp shows the BGP configuration).

Why is backing up a router's configuration to its own flash memory not considered a good backup strategy?

If the router itself fails or is destroyed, both the running device and the backup are lost — backups should be stored on a separate device (e.g., a TFTP server).

When restoring a configuration by copying a backup file to the startup configuration, does it replace or merge with the existing startup configuration?

It merges with the existing configuration rather than replacing it.

If you want to fully replace the startup configuration with a backup (rather than merge), what must you do first?

Erase the existing startup configuration before copying the backup file to it.

What command erases the startup configuration on an older Cisco router?

write erase