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Help System

Invoked using a ? at the command line:

  • ?—Provides a list of all commands at the particular prompt

  • ? following a letter or partial command—Supplies all commands that begin with that letter or letters

  • ? following a command word—Provides additional parameters for command

help—Provides help on using the help system

Router memory types:

    ROM contains the power-on self test and the bootstrap program for the router.

    NVRAM (nonvolatile RAM) stores the startup configuration file for the router.

    Flash RAM is used to store the Cisco IOS that runs on your router.

    RAM provides the temporary storage of information and holds information such as the current routing table. RAM also holds the currently running router configuration.

Basic Command Summary




Enters the privileged mode using the privileged password from the user mode.


Exits the privileged mode to the user mode.

show running-config

Privileged command that shows the router configuration currently running in RAM.

show startup-config

Privileged command that shows the router configuration stored in the router's NVRAM. It's loaded by the router when the router is rebooted.

show CDP neighbor

Shows the routers that are directly connected to your router by LAN or serial connections.

show CDP neighbor detail

Shows more detailed information on routers directly connected to a router.

show clock

Shows the time and date settings for the router.

show flash

Shows the IOS file or files contained in the router's Flash RAM and the amount of total Flash RAM and used Flash RAM.

show history

Shows a list of your last 10 commands.

show hub

Shows information on the status of the hub ports of a 2505 router.

show interface ethernet [interface number]

Shows the current configuration of a specified Ethernet interface.

show interface serial [interface number]

Shows the current configuration of a pecified serial interface.

show interfaces

Lists all the interfaces on the router and statistics related to the interface, such as their current configuration and encapsulation. Also tells you whether the interface is active.

show processes

Shows CPU utilization information.

show protocol

Lists the routing protocols configured on the router.

show version

Shows the version of the IOS currently running on the router.

Editing Commands

Command Keys



Moves the cursor to the beginning of the command line.


Moves the cursor to the end of the command line.


Moves the cursor forward one word on the command line.


Moves the cursor back one word on the command line.


Moves back one character on the command line, deleting the character to the left of the cursor.


Moves forward one character from the cursor.


Moves backward one character from the cursor.

Command abbreviation followed by Tab

Completes the abbreviated command (sh becomes show).


Same as the up arrow, shows most recent command in History.


Same as down arrow, moves backward through the History.


Telnet is an Application layer protocol in the TCP/IP stack. It provides a way to connect to a router over the network from another device.

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