Router Modes

The IOS has various levels of access , called modes. Each mode allowing a user to perform certain tasks.  At the lowest level only basic command and view command can be issued, at the highest level, ip addresses can be set and password set etc.

When a router loads, the first level that the user is given access to is user exec mode.  This is signified by a Router> at the cursor

You find the router will sit waiting for a command from the user as shown below
image022

This User Exec  mode is the basic mode and In general, the user EXEC commands allow you to connect to remote devices, change terminal settings on a temporary basis, perform basic tests, and list system information. It does not allow you to make any major changes and is therefore not very powerful.

From user Exec mode, you can move up to Privileged Exec mode by issuing the command ‘enable’

Router>enable

(This can be reversed by entering the disable command.)

You can see that the > changes to a #  and the prompt Router# is now shown

Privileged EXEC mode allows the use of all EXEC mode commands available on the system and allows access to global configuration mode through the use of the configure terminal command. It is recommended that this is password protected.
Some of the commands that are available include these commands that you should find in all devices, be they routers, switches, or firewalls

cd: Change the current directory. Routers and switches have several file systems, including flash, nvram, system, and null.

clear: Resets functions operating on the device. There are many values that are totaled for reporting that can be reset this way. You can also reset many system-wide configuration values.

clock: Allows you to change the system clock.

copy: Copy a file from one location to another. The location could be another local file system or a remote file system, such as a Trivial File Transfer Protocol (TFTP) server.

debug: Turn on debug logging. This can be done for a specific interface or software component, or for all functions. This places a load on the device if the debugging level is too high and generates an incredible level of messaging on the console screen.

delete: Removes a file from a file system.

dir: Displays the list of files in the current directory.

disable: Reverts the current session back to User EXEC mode and disables the privileged commands.

erase: Removes all files in a file system. This is similar to an OS-level format command.

exit: Exits from Privileged EXEC mode.

no: Reverses a previously issued command. For example, debug all turns on all possible debugging, whereas no debug all turns off all possible debugging. Just about every command that can be issued can be reversed with the no command.

ping: Sends ping or ICMP echo request packets to a remote IP host, such as a switch or router.

pwd: Displays what the current file system directory is.

reload: Restarts the device. This restart can be immediate or scheduled for the future. The reload command can also be used to cancel a scheduled reload.

send: Sends a message to specific or all connected users. This is useful if you are about to perform certain maintenance tasks, such as rebooting the device.

show: Displays configuration information. This is typically configuration information that is running, but it could also be used to view the startup configuration.

systat: Displays information regarding management connections to this device.

telnet: Opens a Telnet connection to a remote device, such as a router or switch.

test: Tests subsystems, memory, and interfaces as part of your diagnostic or troubleshooting process.

traceroute: Traces a route to a destination displaying connectivity results along the path.

undebug: Disables debug commands that were set. This is an alternative to using the no command to perform these functions.

write: Copies information in the running-config buffer to another location, such as memory, a TFTP server, or to the virtual terminal (vty) or console connection.

Global Configuration Mode Router(config)#

To configure a Cisco network device you must enter the Global Configuration operating mode. After first going through User EXEC and Privilege EXEC modes

To enter global configuration mode, use the configure terminal command from privileged EXEC mode. The router prompt for global configuration mode is indicated by the prompt Router(config)# .

This prompt is identified by the (config), which is in the prompt. You also have a different list of commands that you can type. Here is just a sample of the commands at this level:

  • access-list: Manage Access Control Lists (ACLs) to restrict network connections to, from, or through the device you are connected to.
  • arp: Manage the Address Resolution Protocol (ARP) cache on the device you are connected to.
  • banner: Set a logon banner to issue a security warning to users connecting to the device you are connected to.
  • boot: Configure or modify the system boot parameters, such as the IOS version that will be used.
  • cdp: Cisco Discovery Protocol (CDP) tells you what is connected to you on network interfaces. CDP allows you to view this information.
  • clock: Allows you to change the system clock.
  • config-register (router only): Set the configuration register, which is the location in memory that stores a pointer to the system configuration information.
  • enable: Sets or changes enable passwords.
  • exit: Exits Global Configuration mode.
  • hostname: Sets the device hostname.
  • ip: Enters the IP configuration subcommands.
  • interface: Selects an interface for configuration.
  • no: Negates another command that has been issued.

These are the most common modes that you will be using.  To obtain help in any mode simply type ? followed by enter.  This will show a list of commands available.

If you are not sure of the syntax of a command, type the command and then a ? followed by enter.  The CLI will give you the syntax of the command.

The use of ? is not substitute for having a good understanding of the commands available and their use.

As stated earlier the 3 modes above are where you will be doing most of the router configuration, monitoring and troubleshooting.  However there is another mode that come in useful in certain situations.  This is called ROM Monitor.  This mode is designated by the prompt ROMMON>

ROMMON is a bootstrap program, which is a cut down operating system that resides in the ROM in Cisco devices that helps to initialize the processor hardware and boot the operating system software (Cisco IOS).

Since it’s only a mini OS that has a very limited set of commands you can’t do any configuration such as configuring routing, ip addressing, etc from ROMMON. The power of the ROMMON is that you can do very useful things such as password recovery procedure when the password is lost for the device. ROMMON is also useful when downloading IOS software through serial connection, and upgrading your Cisco IOS.

Router Modes – Exercise
Connecting a PC to a router and connecting it to the console to investigate modes.

In this exercise you will connect a PC to a Router and navigate your way through the various modes on the router.

First connect the Rollover cable to the com port on the PC.

Connect the other end to the Router and ensure the router is switched on.

Start your terminal emulation software (such as Putty or HyperTerminal)

Set the settings for the serial port (baud rate 9600 etc)

You should have a connection to the router and see a screen similar to the following.  If you do press Return
image023
If the router is asking if you want to enter System Configuration Dialog type ‘no’ and press enter.

You should now be at the Router> prompt

Type ? and then press enter to see a list of commands available in this mode

Which mode is this?

Now type enable

The router prompt should have changed to Router#

Type ? and then press enter to see a list of commands available in this mode

Which mode is this?

 

Now type Configure Terminal

The router prompt should have changed to Router(config)#

Type ? and then press enter to see a list of commands available in this mode

Which mode is this?

 

Now type exit and press return

Which mode are you in now?

Type exit again

Which mode are you in now?

Repeat the exercise to familiarise yourself with the different modes of the router before attempting the worked example below.

Next – Worked Example