Screen output varies, depending on Cisco IOS Software level and router configuration.Router Help Functions Suppose that a user wants to set the router clock.. debug Debugging functions se
Trang 1Screen output varies, depending on Cisco IOS Software level and router configuration.
Router Help Functions
Suppose that a user wants to set the router clock If the necessary command is not
known, that user can use the help function to check the syntax for setting the clock
The following exercise illustrates one of the many uses of the help function The task is
to set the router clock Assuming that the command is not known, proceed using the
following steps:
Step 1 Use ? to find the command for setting the clock The help output shows
that the clock command is required
Step 2 Check the syntax for changing the time
Step 3 Enter the current time by using hours, minutes, and seconds, as shown
The system indicates that additional information needs to be provided to complete the command The help output in Example 11-12 shows that
the set keyword is required
debug Debugging functions (see also 'undebug')
delete Delete a file
dir List files on a filesystem
disable Turn off privileged commands
disconnect Disconnect an existing network connection
elog Event-logging control commands
enable Turn on privileged commands
erase Erase a filesystem
exit Exit from the EXEC
help Description of the interactive help system
More Example 11-12 Clock set Keyword
Cisco# clok
Translating "clok" domain server (255.255.255.255)
% Unknown command or computer name, or unable to find computer address
continues
Example 11-11 Privileged EXEC Mode Commands (Continued)
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Step 4 Check the syntax for entering the time, and enter the current time using
hours, minutes, and seconds As shown in Example 11-13, the system again indicates that additional information is required to complete the command
Cisco# cl?
clear clock
Cisco# clock
% Incomplete command.
Cisco# clock ? set Set the time and date
Cisco# clock set
% Incomplete command.
Cisco# clock set ? hh:mm:ss Current Time
Example 11-13 Clock Time and Date Set Format
Cisco# clock set 19:50:00
% Incomplete command.
Cisco# clock set 19:50:00 ? <1-31> Day of the month MONTH Month of the year
Cisco# clock set 19:50:00 14 7 ^
% Invalid input detected at '^' marker.
Cisco# clock set 19:50:00 14 July
% Incomplete command.
Cisco# clock set 19:50:00 14 July ? <1993-2035> Year
Example 11-12 Clock set Keyword (Continued)
Trang 3Step 5 Press Ctrl + P or the up arrow to repeat the previous command entry
automatically Then add a space and a question mark (?) to reveal the additional arguments Now the command entry can be completed
Step 6 The caret symbol (^) and help response indicate that there is an error
The placement of the caret symbol shows where the possible problem
is located To input the correct syntax, re-enter the command up to the
point where the caret symbol is located, and then enter a question mark (?).
Step 7 Enter the year, using the correct syntax, and press Enter to execute the
command
The user interface provides syntax checking by placing a ^ where the error occurred
The ^ appears at the point in the command string where an incorrect command,
key-word, or argument was entered The error location indicator and interactive help system
enable syntax errors to be found and easily corrected
Cisco IOS Software Editing Commands
The user interface includes an enhanced editing mode that provides a set of editing
key functions with which the user can edit a command line as it is being typed Use
the key sequences indicated in Table 11-2 to move the cursor at the command line for
corrections or changes Although enhanced editing mode automatically is enabled with
the current software release, it can be disabled if written scripts do not interact well
while enhanced editing is enabled To disable enhanced editing mode, type terminal no
editing at the privileged EXEC mode prompt.
Cisco# clock set 19:50:00 14 July 2003
Cisco#
Table 11-2 Editing Commands
Command Description
continues
Example 11-13 Clock Time and Date Set Format (Continued)
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The editing command set provides a horizontal scrolling feature for commands that extend beyond a single line on the screen When the cursor reaches the right margin, the command line shifts ten spaces to the left The first ten characters of the line cannot
be seen, but a user can scroll back and check the syntax at the beginning of the com-mand To scroll back, press Ctrl+ b or the left arrow key repeatedly until the beginning
of the command entry is reached Ctrl + a returns a user directly to the beginning of the line
In Example 11-14, the command entry extends beyond one line When the cursor first reaches the end of the line, the line is shifted ten spaces to the left and is redisplayed The dollar sign ($) indicates that the line has been scrolled to the left Each time the cursor reaches the end of the line, the line again is shifted ten spaces to the left
Screen output varies, depending on the Cisco IOS Software level and router configuration The Ctrl + z command backs out of configuration mode This command returns the user to the privileged EXEC mode prompt
Router Command History
The user interface provides a history, or record, of commands that have been entered This feature is particularly useful for recalling long or complex commands or entries With the command history feature, the following tasks can be completed:
■ Set the command history buffer size
■ Disable the command history feature
Example 11-14 Extension of Command Entry
Cisco>$ value for our customers, employees, investors, and partners
Table 11-2 Editing Commands (Continued)
Command Description
Trang 5By default, the command history is enabled and the system records ten command lines
in its history buffer To change the number of command lines that the system records
during a terminal session, use the terminal history size or the history size commands
The maximum number of commands is 256 Table 11-3 shows command history
commands
To recall commands in the history buffer, beginning with the most recent command,
press Ctrl + p Continue to press Ctrl + p or the up arrow key to recall successively
older commands To return to more recent commands in the history buffer, after using
the Ctrl + p or the up arrow, press Ctrl + n or the down arrow key repeatedly to recall
successively more recent commands
When typing commands, as a shortcut, you can enter the unique characters for a
com-mand Press the Tab key, and the interface finishes the entry When the typed letters
uniquely identify the command, the Tab key simply acknowledges visually that the
router has understood the specific command that was intended
On most computers, additional select and copy functions are available A previous
command string can be copied and then pasted or inserted as the current command
entry
Table 11-3 Router Command History
recalls the last (previous) command
recalls the most recent command
terminal history [size numberof-lines] Sets the command buffer size
terminal no editing Disables advanced editing features
Router> terminal editing Re-enables advanced editing features
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Cisco IOS Software Fundamentals
Like any computer, a router or switch cannot function without an operating system Cisco calls its operating system the Cisco Internetwork Operating System, or Cisco IOS Software It is the embedded software architecture in almost all of the Cisco routers and Catalyst switches Some Catalyst switches use a Cisco command-line interface (CLI) A router does not become functional until it loads Cisco IOS Software Without
an operating system, the hardware has no capability Cisco IOS Software provides the following network services:
■ Basic routing and switching functions
■ Reliable and secure access to networked resources
■ Network scalability
Operation of Cisco IOS Software
Cisco IOS Software devices have three distinct operating environments or modes:
The startup process of the router normally loads into RAM and performs in one of these operating environments The configuration register setting can be used by system administrators to control which of these modes is used by the router to load
The ROM monitor performs the bootstrap process and provides low-level functionality and diagnostics The ROM monitor is used to recover from system failures and to recover a lost password The ROM monitor cannot be accessed through any of the network interfaces, but only through a console port session
When the router is running in boot ROM mode, only a limited subset of the Cisco IOS Software feature set is available Boot ROM allows write operations to Flash memory and is used primarily to replace the Cisco IOS Software image that is stored in Flash
Lab Activity Command Line Fundamentals
In this lab, you log into a router in both user and privilege modes You use several basic router commands to determine how the router is configured You also become familiar with the router help facility and use the command history and editing features
Trang 7memory The Cisco IOS Software image can be modified in boot ROM mode by using
the copy tftp flash command, which copies an IOS image stored on a TFTP server into
the Flash memory of the router
The normal operation of a router requires the full Cisco IOS Software image from
Flash memory In some devices, the IOS is performed directly from Flash However,
most Cisco routers require a copy of the Cisco IOS Software image to be loaded into
RAM and also executed from RAM Some Cisco IOS Software images are stored in
Flash in a compressed format and must be expanded when copied to RAM
To see the Cisco IOS Software image and version that is running, use the show version
command, which also indicates the configuration register setting The show flash
com-mand in Example 11-15 verifies that the system has sufficient memory to load a new
Cisco IOS Software image
Cisco IOS Software Features
Cisco provides Cisco IOS Software images for devices spanning a wide range of
net-work product platforms To optimize the Cisco IOS Software required by various
product platforms, Cisco is working to develop many different Cisco IOS Software
images Each image represents a different feature set that serves the various device
platforms, available memory resources, and customers’ needs
Numerous Cisco IOS Software images exist for different Cisco device models and
feature sets However, the basic configuration command structure is the same The
configuration and troubleshooting skills acquired on any one device apply across a
wide range of products
The naming convention for the different Cisco IOS Software releases contains three parts:
■ The platform on which the image runs
■ The special capabilities supported in the image
■ Where the image runs and whether it has been zipped or compressed
Example 11-15 Verifying the Cisco IOS Software Image
Cisco> show flash
System flash directory:
File Length Name/status
1 8022152 /c2500-i-l.121-16.bin
[8022216 bytes used, 366392 available, 8388608 total]
8192K bytes of processor board System flash (Read ONLY)
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This material is covered in more detail in Chapter 14, “Managing Cisco IOS Software.” The Cisco IOS Software naming conventions, image content, and other details are subject to change
After choosing the options that meet the network requirements, select a Cisco IOS Software release that is supported by the hardware The software requirements of each device are listed in the “Cisco Product Documentation” section of the Documentation
CD The Cisco Software Advisor is an interactive tool that provides the most current information
One of the main considerations when selecting a new IOS image is that it is compatible with the router flash and RAM memory In general, the newer the release is and the
more features it provides, the more memory it requires Use the show version
com-mand, as shown in Example 11-13, from the Cisco device to check the current image and available Flash memory The Cisco support site has tools available to help determine the amount of Flash memory and RAM required for each image
Before installing a new Cisco IOS Software image on the router, check to see if the router meets the memory requirements for that image To see the amount of RAM,
issue the show version command and look for the following output in Example 11-16.
The highlighted line shows how much main and shared memory is installed in the router Some platforms use a fraction of dynamic RAM (DRAM) as shared memory The memory requirements take this into account, so both numbers must be added to determine the amount of DRAM installed on the router
To determine the amount of free Flash memory, issue the show flash command, as
shown in Example 11-17
Example 11-16 show version Command Output
Cisco> show version Cisco Internetwork Operating System Software output omitted
image file is "flash:/c2500-i-l.121-16.bin"
cisco 2600 (68030) processor (revision N) with 6144K/2048K bytes of memory.
Trang 9The show version Command
The show version command displays information about the Cisco IOS Software version
that currently is running on the router This includes the configuration register and the
boot field setting
■ Cisco IOS Software version and descriptive information
■ Router up time
■ Last restart method
■ System image file and location
■ Router platform
■ Configuration register setting
Router User Interface
Recall that the Cisco IOS Software uses a command-line interface (CLI) as its
tradi-tional console environment Cisco IOS Software is a core technology that extends
across most of the Cisco product line Its operation details vary, depending upon the
internetworking device using it
This CLI environment is accessible through several methods:
■ Through a console session A console uses a low-speed serial connection directly
from a computer or terminal to the console connection on the router This method does not require the configuration of network services on the router
■ Through a dialup connection by using a modem or a null modem connected to
the router AUX port This method does not require the configuration of network services on the router, either
Example 11-17 show flash Command Output
Cisco> show flash
System flash directory:
File Length Name/status
1 8022152 /c2500-i-l.121-16.bin
[8022216 bytes used, 366392 available, 8388608 total]
8192K bytes of processor board System flash (Read ONLY)
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■ Through a Telnet connection to the router as a virtual terminal To establish a Telnet session to the router, at least one interface must be configured for IP Virtual terminal sessions also must be configured for login and passwords
Router User Interface and Modes
The Cisco CLI uses a hierarchical structure This structure requires entry into different modes to accomplish particular tasks For example, interface configuration mode must
be entered to configure a router interface From interface configuration mode, all con-figurations entered apply only to that particular interface Each command mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode
Cisco IOS Software provides a command interpreter service known as the command executive (EXEC) After each command is entered, the EXEC validates and executes the command
As a security feature, Cisco IOS Software separates the EXEC sessions into two access levels These levels are user EXEC mode and privileged EXEC mode, which is also known as enable mode
User EXEC mode allows only a limited number of basic monitoring commands This often is referred to as a view-only mode The user EXEC level does not allow any com-mands that could change the configuration of the router The user EXEC mode can be identified by the > prompt
Privileged EXEC mode provides access to all router commands Privileged EXEC mode can be protected by requiring a user ID and a password This mode allows only autho-rized users to access the router Configuration and management commands require that the network administrator be at the privileged EXEC level Global configuration mode and all other more specific configuration modes can be reached only from privi-leged EXEC mode Priviprivi-leged EXEC mode can be identified on the CLI session by the
# prompt
To access the privileged EXEC level from the user EXEC level, enter the enable
com-mand at the > prompt If a password is configured, the router asks for a password at this point For security reasons, a Cisco network device will not show the password that is entered When the correct password is entered, the router prompt changes to #, indicating that the user is now at the privileged EXEC level Entering a question mark (?) at the privileged EXEC level reveals many more command options than those avail-able at the user EXEC level