Let's look at how you log in to a Cisco router.
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Here, you are connected to the router by the asynchronous serial console port.
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The Cisco IOS command interpreter, EXEC, interprets the commands you type and carries out the corresponding operations.
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You need to log in to the router before you can enter an EXEC command.
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So you press £UReturn£u.
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When you first log in you see the user EXEC mode prompt.
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You can type £R?£r at the prompt to display a list of available commands.
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The More prompt indicates that there are more commands to see.
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If you press £UReturn£u, you see the next line.
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You can see the contents of the next whole screen by pressing the space bar.
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To exit User mode and log out of the router, you type £Rlogout£r.
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If there is no keyboard entry, the session will timeout and you will have to hit Enter again to get started.
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You enter Privileged EXEC mode by typing £Renable£r at the command prompt.
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Then you enter a password.
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The EXEC prompt is terminated with a hash sign while you are in this mode.
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You can type £R?£r here to see a list of privileged EXEC commands.
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Once again the More prompt indicates further information is available.
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As in User mode, you can see the next line by pressing £UReturn£u.
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Or the contents of the next whole screen by pressing the space bar.
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Notice that many more commands are now available in Privileged mode.
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You can press any key to return to the system prompt.
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To exit back to User mode you type £Rdisable£r.
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When you have finished working with the router you can exit the user interface by typing £Rlogout£r.
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You can abbreviate the Logout command to £Rlogo£r.
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This logs you out and ends your current session with the router.
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<F>You can use the context-sensitive help features of the Cisco IOS to determine the command that you need to perform a given task.
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Suppose you want to set the router clock.
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You can obtain a list of commands that begin with a particular character sequence by typing those characters followed immediately by a question mark.
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When using context-sensitive help, the space (or lack of a space) before the question mark (?) is significant.
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This form of help, in which characters are followed immediately by a question mark, is called £Rword help£r because it completes a word for you.
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When you discover the correct command to use, it still may not be complete on its own.
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You can use help to check the syntax for setting the router clock.
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You type the command, add a space, and then type £R?£r.
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The help output shows that the Set keyword is required.
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This form of help is called £Rcommand syntax help£r, because it reminds you which keywords or arguments are required to continue a command.
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Next you can check the syntax for entering the time.
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Then you enter the current time using hours, minutes, and seconds, as shown here.
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In the example shown here, the system indicates that you need to provide additional arguments to complete the command.
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<F>You press £UCtrl+P£u to repeat the previous command entry automatically.
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Then you add a space and a question mark to reveal additional arguments. The output tells you that you need two more arguments.
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If you enter an incorrect command, the caret symbol (£R^£r) and help response indicate the error.
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Notice that the caret symbol character is displayed at the point in the command string where the IOS detected that you entered an incorrect command, keyword, or argument.
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This error location facility together with the interactive help system allows you to find and correct syntax errors easily.
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In this case you press £UCtrl+P£u to recall the last command you typed, and you add a space and type £R?£r.
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Here, another required parameter is displayed.
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Now you can complete the command entry and press £UReturn£u to execute the command.
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<F>The Cisco user interface includes an enhanced editing mode that provides a set of editing key functions.
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Enhanced editing mode is automatically enabled.
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You can disable Enhanced Editing mode and revert to the editing mode of previous Cisco IOS releases.

For example, you might want to disable Enhanced Editing mode if you have pre-built scripts that don't interact well if it is enabled.
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The editing command set provides a horizontal scrolling feature for commands that extend beyond a single line on the screen.
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When the cursor reaches the right margin, the command line shifts ten spaces to the left.
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The dollar sign indicates that the line has been scrolled.
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You can scroll back to the start of the line by pressing £UCtrl+B£u (or the £Uleft arrow£u key) repeatedly.
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If you press £UEsc+B£u you move back a word at a time.
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Alternatively, you can press £UCtrl+A£u to return directly to the start of the line.
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You can use several Cisco IOS commands to examine the status of a router.
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Each command allows you to examine a different configurable component of the router.
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You log in to the router and enter privileged mode.
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You type £Rshow version£r to display the configuration of the system hardware, the software version, the names and sources of configuration files, and the boot images.
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Here you can see

• the current version of 
  the Cisco IOS being used
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• how long the router has 
  been up
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• how the system was 
  restarted
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• where the operating 
  system was loaded from
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You press the space bar to see the next screen.
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You can find information about the router's interfaces.
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And you can check the value of the configuration register.
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To display information about the active processes you type £Rshow processes£r.
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First you can check the overall CPU utilization in the previous five seconds, minute, and five minutes.
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PID represents the ID number of each process.
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Q tells you the process queue priority (£RH£righ, £RM£redium, or £RL£row).
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Ty represents a test of the status of the process.
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PC is the current program counter.
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Runtime (in milliseconds) denotes the CPU time that the process has used.
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Invoked represents the number of times the process has been invoked.
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uSecs tells you the microseconds of CPU time for each process invocation.
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Stacks shows you the low watermark/total stack space available, in bytes.
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TTY tells you which terminal controls the process.
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Process displays the name of the process.
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To see how the management system allocates memory for different purposes in the router you type £Rshow memory£r.
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The first section of the display includes summary statistics about the activities of the system memory allocator.
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The information here includes the amount of memory in use, and the size of the largest available free block.
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The second section of the display is a block-by-block listing of memory use.
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You can scroll down to see more, and you type £Rq£r to quit back to the privileged mode prompt.
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You can get a closer look at the buffers by typing £Rshow buffers£r.
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You can see from the example shown here that there are different buffer sizes available.
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<F>You can examine flash memory more closely by typing £Rshow flash£r.
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You can also see the size of the files, and the amount of flash memory free.
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You can see what hardware interfaces are on the router by typing £Rshow interfaces£r.
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In this example, you press the space bar to see the details of the Ethernet (E0) interface.
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You can show what protocols are configured on the router by typing £Rshow protocols£r.
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In the example shown here, IP is running, but the other protocol options are not.
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IP is configured on the Ethernet interface and on the serial ports.
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You can examine IP further by typing £Rshow ip protocol£r.
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<F>In this example, IP is using RIP as its routing protocol.
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Let's log in to a router, SanFran, now.
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You press £UReturn£u to get started.
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Now that you are in User Mode, let's access privileged mode.
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You type £Renable£r to access Privileged mode.
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You can also abbreviate the enable command to £Ren£r, £Rena£r, and so on.
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Then you supply a password.
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The prompt indicates that you are now in Privileged mode.
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You type £R?£r to see Privileged mode commands.
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And you press the space bar to see each screen of information.
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You type £Rdisable£r to exit Privileged mode and get back to User mode.
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You can abbreviate the disable command to £Rdisa£r, £Rdisab£r, or £Rdisabl£r.
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Let's end this session now by logging out.
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You type £Rlogout£r to log out of the router.
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You can abbreviate the Logout command to £Rlogo£r.
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This ends the session.
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Let's use Cisco commands to examine the status of some of a router's configurable components.
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Assume you have logged in and have entered Privileged mode.
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First we'll check the version of the Cisco IOS.
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You type £Rshow version£r to see the version of Cisco IOS.
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The Cisco IOS version number is shown here.
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The information displayed includes how long the router is up.
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You can see how the system restarted.
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You can then press £Uspace£u bar to see more.
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Alternatively, you can press £UEnter£u to see more information one line at a time.
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Here you can see the value of the configuration register.
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This setting of the register indicates that the router should load a Cisco IOS image from flash memory.
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Now let's examine the processes that are running on the router.
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You can see which processes are running on the router by typing £Rshow processes£r.
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The EXEC process has PID 1.
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It has medium priority and is currently running.
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The asterisk (*) indicates that a process is currently running.
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You can also see the CPU time the process has used (in milliseconds), the number of times the process has been invoked, and the microseconds of CPU time for each process invocation.
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If you press £Uspace£u bar in this case you return to the router prompt.
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Say you press £UCtrl+P£u to recall the command and look at the processes again.
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You can see that the processes information has changed.
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Now let's examine how the memory management system allocates memory for different purposes in the router.
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You type £Rshow memory£r to examine the memory statistics.
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The first section deals with the activities of the system memory allocator.
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And the second gives you a block-by-block listing of memory use.
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You quit back to the router prompt by typing £Rq£r.
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Let's look now at the router's interfaces.
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You can see what hardware interfaces are on the router by typing £Rshow interfaces£r.
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You press the space bar to see the details of the Ethernet (E0) interface.
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Here you can see the physical, burned-in address (bia) of the interface.
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You can also check the serial interfaces.
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In this example, both are configured.
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Let's look finally at what protocols are running on the router.
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You type £Rshow protocols£r to display the protocols that are configured on the router.
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So in this case IP is enabled.
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And you also see the associated configuration information for each of the router's interfaces.
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