Appendix A - Using Cisco IOS Software

Table Of Contents

Using Cisco IOS Software

Accessing the Command-Line Interface

Connecting Using Telnet

Connecting to the Console Port

Understanding the Command-Line Interface

Command Modes

User EXEC Mode

Privileged EXEC Mode

Global Configuration Mode

Interface Configuration Mode

Context-Sensitive Help

Command History Features

Displaying the Command History

Editing Previous Commands

Command History Buffer Size

Using Output Modifiers

Understanding Cisco IOS Configuration Files

Downloading the Configuration File

Startup and Run-Time Configuration Files

Displaying the Configuration Files

File Format

Useful Commands

Using Cisco IOS Software

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This appendix describes the basics about using the Cisco IOS software that is installed on every Cisco uBR905 and Cisco uBR925 cable access routers:

•Accessing the Command-Line Interface

•Understanding the Command-Line Interface

•Understanding Cisco IOS Configuration Files

•Useful Commands

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Caution Before attempting to reconfigure the cable access router at a subscriber site, contact your provisioning or billing system administrator to ensure remote configuration is allowed. To ensure proper levels of service for all customers, service providers typically disable remote configuration of the cable modems on their system and allow only the configuration that is specified by the cable provisioning or billing system.

If remote configuration is disabled, any changes you make do not remain in effect after the cable access router is powered off and on, and the router returns to its previous configuration. In some cases, these settings will cause the cable interface to disconnect and may be lost when the cable interface is reset.

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Accessing the Command-Line Interface

The Cisco uBR905 and Cisco uBR925 cable access routers' command-line interface (CLI) can be accessed either through a Telnet connection over a TCP/IP network or by a direct connection to the router's console port. See the following sections for more information.

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Note The Cisco uBR905 and Cisco uBR925 cable access routers also support accessing the CLI through the Cisco web server, but this feature is automatically disabled when the Cable Monitor is active. See "Using the Cable Monitor Tool" for details.

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Connecting Using Telnet

If the cable access router has successfully booted up and is operational and online, you can access its CLI interface by establishing a Telnet connection. Telnet can be used from any computer or terminal that has TCP/IP connectivity with the cable access router. The TCP/IP connectivity can exist either through the Ethernet interface or the cable interface.

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Note As a security measure, you can enter EXEC mode during a Telnet session only if an enable password has been set on the router. If an enable password has not been set, you can display only the current configuration when you log in using Telnet. To change the configuration you must log in through the router's console port.

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Caution Care must be taken if you use a laptop computer to make a Telnet connection through the cable access router's Ethernet, either by connecting the laptop directly to one of the router's Ethernet ports, or by connecting the laptop to a hub that is connected to one of the router's Ethernet ports. If the laptop computer will not be regularly used at the subscriber site, you should power cycle the cable access router after you use the CLI and save your configuration changes. This is also necessary when connecting the laptop to the USB port on the Cisco uBR925 cable access router.

Power cycling the cable access router ensures the laptop computer does not remain in the router's list of allowable Customer Premises Equipment (CPE) devices at the subscriber site. Reinitialization of the cable interface clears out the bridge table and resets the counter that specifies the number of CPE devices being bridged. This is particularly important when the cable access router is configured to operate in a DOCSIS-compliant bridging mode.

If the headend is a Cisco uBR7200 series universal broadband router, the system administrator at the headend might have to issue the clear cable modem host mac address command to remove the laptop computer from its list of CPE devices.

This behavior is required by the DOCSIS specification.

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Connecting to the Console Port

The router's CLI is available by connecting directly to the console port on the back panel of the router. The console port is an EIA/TIA-232 serial interface configured as data communications equipment (DCE) and uses an RJ-45 connector. The port is wired the same as other Cisco routers and uses the same console kit and cable.

The console port can be accessed by any computer or terminal with an RS-232 serial port set for 9600 baud, 8 data bits, no parity, 1 stop bit (9600 8N1). Unless the router's default configuration has been changed, your terminal software should be set to emulate an ANSI, VT100, or compatible terminal.

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Note Typically, the console port is disabled when the CMTS downloads a Cisco IOS configuration file to the router. If this is the case, the CLI can be accessed only through a Telnet connection.

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Understanding the Command-Line Interface

The Cisco IOS command-line interface (CLI) is a text-based interface available on every Cisco router that uses the Cisco IOS software. This allows a network administrator to quickly configure many different models of Cisco routers without having to learn a unique interface for each model.

The following guidelines apply to the CLI:

•The CLI is case-insensitive. For example, you can enter either SHOW VERSION or show version to display the cable access router's software revision.

•You can abbreviate commands and keywords to the minimum number of characters that define a unique abbreviation. For example, you can abbreviate the show command to sh (but you cannot abbreviate the show command to just s because several other commands also start with the letter s).

•If you enter an unrecognized command, the router assumes the command is actually the host name of a PC or other router and tries to open a Telnet connection to it. If the router cannot find that host, the connection will eventually time out and the CLI prompt will reappear.

•By default, if a command displays more than one screen of data, it pauses the screen and displays --More-- at the bottom of the screen. You can advance one line at a time by pressing the Return key, advance one screen at a time by pressing the spacebar, or quit by pressing q.

•As a general rule, every configuration command can be disabled by prefixing the command with the keyword no. For example, IP routing is enabled with the ip routing command, and is disabled with the no ip routing command.

•The CLI on the cable access router can be accessed either through a Telnet connection or through a serial connection with its console port. (Web browser access to the CLI is not supported on the cable access router when the Cable Monitor is active.)

These additional topics are covered in the sections that follow:

•The CLI contains many different command modes that allow access to different areas of the cable access router's configuration. Certain commands are available only in a specific command mode. See the next section, "Command Modes".

•The question mark character (?) displays a list of the available commands and can be used to display help about a specific command. See the "Context-Sensitive Help" section.

•You can use the command history feature to quickly recall and edit previous commands. See the "Command History Features" section.

•When commands produce long displays, you can use output modifiers to select which parts of the display you want to see. See the "Using Output Modifiers" section.

Command Modes

The Cisco IOS software has many different modes of operation. Each mode contains its own set of commands that either display or configure a particular aspect of the cable access router's configuration. When you initially log in to the cable access router, you enter user EXEC mode, which provides a limited number of commands that can only display information about the router; you cannot change the router's configuration in user EXEC mode.

To change the router's configuration, you must enter privileged EXEC mode or one of the other configuration modes. Each command mode has a unique prompt so that you can easily see which mode you are in.

Table A-1 shows the most common modes that are used on the cable access router:

Table A-1 Cisco uBR905 and Cisco uBR925 Router Command Modes

Command Mode	Function	Access Method	Prompt 1
User EXEC	Contains a limited number of commands that only display information about the cable access router.	Log in.	Router>
Privileged EXEC	Contains a larger number of display commands, as well as other commands that can change the configuration of the router. Also provides access to the global configuration mode.	From user EXEC mode, enter the enable command.	Router#
Global configuration	Contains commands that can change the operation of the cable access router at a system level and provides access to the interface configuration mode.	From privileged EXEC mode, enter the configure terminal command.	Router(config)#
Interface configuration	Contains commands that change the operation of the router's Ethernet and cable interfaces.	From global configuration mode, enter the interface interface-num command.	Router(config-if)#

1 The prompt always displays the router's hostname. The default hostname is "Router" but this can be changed with the global configuration hostname command.

Table A-1 lists the command modes in the order that they must be accessed. You must log in to a higher-level mode before accessing the next lower mode. For example, before you can enter global configuration mode, you must first log in to user EXEC mode and then privileged EXEC mode. Then you can enter global configuration mode, and if desired, log in to interface configuration mode.

To leave a command mode and return to the previous mode, enter either the exit or end command. See the following sections for more details on each command mode.

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Note For complete information on using the CLI, see the Configuration Fundamentals Configuration Guide, available on CCO and the Documentation CD-ROM.

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User EXEC Mode

When you log in to the cable access router, you automatically enter the user EXEC command mode, which contains commands that only display some parts of the router's configuration. In general, user EXEC commands allow you to connect to remote devices, change terminal settings on a temporary basis, perform basic tests, and list system information.

The user-level prompt consists of the router's name followed by a right angle bracket (>):

Router>

To leave user EXEC mode and log out of the cable access router, enter the logout or exit command.

Privileged EXEC Mode

Before you can enter any commands that change the cable access router's configuration, you must enter privileged EXEC mode. In this mode you can change certain router parameters, use more detailed show commands, and use other configuration modes to change the operation of the router and its interfaces.

To access the privileged EXEC mode, enter the enable command from user EXEC mode. You are then prompted for a password, if one has been set for the privileged EXEC mode. The password does not appear on the screen and is case sensitive. The prompt changes to the router's host name followed by the pound sign (#) to indicate you are now in privileged EXEC mode.

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Note If an enable password has not been set, privileged EXEC mode can be accessed only from the router console, not through a Telnet connection.

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The following example shows how to access privileged EXEC mode:

Router> enable

Password: <password> 

Router# 

To return from privileged EXEC mode to user EXEC mode, use the disable or exit command.

Global Configuration Mode

The global configuration mode contains commands that change configuration parameters that affect the operation of the entire cable access router, such as routing and bridging functions, as opposed to changing the operation of a single interface. To log in to global configuration mode, enter the configure  terminal from privileged EXEC mode. The prompt changes to the router's host name followed by "(config)#" to indicate that you are now in global configuration mode.

The following example shows how to access global configuration mode:

Router# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Router(config)#

To exit global configuration mode and return to privileged EXEC mode, enter the exit or end command, or press Ctrl-Z.

Interface Configuration Mode

The interface configuration mode configures features for an individual interface. The Cisco uBR905 cable access router supports the following interfaces:

•Ethernet0—Ethernet interface on the back panel of the router

•cable-modem0—Cable interface that connects to the cable network

•Loopback0—Internal interface used primarily for debugging

The Cisco uBR925 cable access router supports the following interfaces:

•Ethernet0—Ethernet interface on the back panel of the router

•cable-modem0—Cable interface that connects to the cable network

•USB0—Universal Serial Bus (USB) interface that connects to a PC

•Loopback0—Internal interface used primarily for debugging

To log in to interface configuration mode, enter the interface command followed by the name of the interface to be configured. The prompt changes to the router's host name followed by "(config-if)#" to indicate that you are now in interface configuration mode.

For example, to configure the cable interface on the cable access router, enter the following commands from global configuration mode:

Router(config)# interface cable-modem 0 

Router(config-if)#

To exit interface configuration command mode and return to global configuration mode, enter the exit command, or press Ctrl-Z.

Context-Sensitive Help

The Cisco IOS CLI contains a context-sensitive help feature that can display a list of the commands that are available for the current command mode. The context-sensitive help can also display the syntax for a particular command, and complete a partially entered command.

Table A-2 shows the different ways you can access the context-sensitive help.

Table A-2 Context-Sensitive Help for the Command -Line Interface

Command	Purpose
help	Obtains a brief description of the help system in any command mode.
?	Lists all commands available for a particular command mode.
partial-command?	Obtains a list of commands that begin with a particular character string. (Do not enter a space before the question mark.)
partial-command<Tab>	Completes a partial command name. (Do not enter a space before entering the tab character.)
command ?	Lists a command's associated keywords. (A space must precede the question mark.)
command keyword ?	Lists a keyword's associated arguments. (A space must precede the question mark.)

The context-sensitive help displays only the commands and options that are appropriate for the current command mode. For example, to display the available show commands in the user EXEC mode, enter show ? as shown in the following example:

 uBR905> show ? 

  backup            Backup status

  bootflash:        display information about bootflash: file system

  call              Show Calls

  cca               CCA information

  class-map         Show QoS Class Map

  clock             Display the system clock

  compress          Show compression statistics

  dial-peer         Dial Plan Mapping Table for, e.g. VoIP Peers

  dialer            Dialer parameters and statistics

  exception         exception information

  flash:            display information about flash: file system

  gateway           Show status of gateway

  history           Display the session command history

  hosts             IP domain-name, lookup style, nameservers, and host table

  location          Display the system location

  num-exp           Number Expansion (Speed Dial) information

  policy-map        Show QoS Policy Map

  ppp               PPP parameters and statistics

  queue             Show queue contents

  queueing          Show queueing configuration

  radius            Shows radius information

  rmon              rmon statistics 

  sessions          Information about Telnet connections

  sgcp              Display Simple Gateway Control Protocol information

  snmp              snmp statistics

  tacacs            Shows tacacs+ server statistics

  template          Template information

  terminal          Display terminal configuration parameters

  traffic-shape     traffic rate shaping configuration

  translation-rule  Show translation rule table

  users             Display information about terminal lines

  version           System hardware and software status

  voice             Voice port configuration & stats 

uBR905> 

Entering the same help command in privileged EXEC or global configuration mode displays a different list of show commands. To display a list of available commands that start with "t" enter the following:

uBR905> t? 

telnet  terminal  traceroute  tunnel

uBR905> 

Command History Features

The CLI command history feature remembers the commands that you have entered during the current session. You can use this feature to repeat or change previous commands without retyping them. See the following sections for more information.

Displaying the Command History

To recall commands from the history buffer, use one of the commands shown in Table A-3.

Table A-3 Recalling Previous Commands

Command	Purpose
Press Ctrl-P or the up arrow key.1	Recalls commands in the history buffer, beginning with the most recent command. Repeat to recall successively older commands.
Press Ctrl-N or the down arrow key.1	Returns to more recent commands in the history buffer after recalling commands with Ctrl-P or the up arrow key. Repeat to recall successively more recent commands.
show history	Lists the last several commands you have just entered (user EXEC mode only).

1 The arrow keys function only on ANSI-compatible terminals such as VT100s.

Editing Previous Commands

When you display a previous command using Ctrl-P or Ctrl-N, you can edit that command to correct any errors or to change a parameter. This allows you to quickly give a series of similar commands without having to retype each command.

Table A-4 shows the most commonly used editing commands.

Table A-4 Editing Previous Commands 

Command 1	Purpose
Press Ctrl-A	Moves to the beginning of the line.
Press Ctrl-B	Moves back one character.
Press <Esc>-B	Moves back to the previous word.
Press Ctrl-D	Deletes the character at the cursor position.
Press Ctrl-E	Moves to the end of the line.
Press Ctrl-F	Moves forward one character.
Press <Esc>-F	Moves forward one word.
Press Ctrl-K	Deletes all characters from the cursor to the end of the line.
Press Ctrl-U or Ctrl-X	Deletes all characters from the cursor to the beginning of the line.
Press Ctrl-W	Deletes a single word.

1 These editing commands are similar to those used in the EMACS text editor.

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Note Additional editing commands are given in the Configuration Fundamentals Configuration Guide, available on CCO and the Documentation CD-ROM.

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Command History Buffer Size

By default, the command history feature stores the ten most recent commands in its history buffer. You can change the size of this buffer for the current terminal session with the terminal history command:

uBR905> terminal history size 20 

uBR905> 

The terminal no history size command resets the number of lines saved in the history buffer to the default of 10 lines.

Using Output Modifiers

Many of the cable access router's commands output a great deal of information that takes many screens to display. You can use the Cisco IOS software's output modifiers to filter the output of almost any command, so that you can display only those lines you are interested in.

The output modifier feature is invoked by using the pipe symbol (|). To use this feature, enter a command as normal but add a space and the pipe symbol at the end of the command line. Then add one of the keywords shown in Table A-5.

Table A-5 Using Output Modifiers

Command	Purpose
begin regular expression	Displays the first line that matches the regular expression, and then all other lines that follow that line.
include regular expression	Displays all lines that match the regular expression.
exclude regular expression	Displays all lines except those that match the regular expression.

To filter the output from the show ip traffic command to display only those lines that include the word "error," enter the following:

uBR905>show ip traffic | include error 

         0 format errors, 0 checksum errors, 1 bad hop count

  Rcvd: 0 format errors, 0 checksum errors, 0 redirects, 4 unreachable

  Total: 0/0, 0 checksum errors, 0 format errors

  Total: 0/0, Format errors: 0/0, Checksum errors: 0/0

  Rcvd: 134 total, 0 checksum errors

  Rcvd: 23 total, 0 checksum errors, 9 no port

  Rcvd: 17 total, 0 checksum errors, 1 no port 

Understanding Cisco IOS Configuration Files

Cisco IOS configuration files are text files that contain Cisco IOS commands to configure the cable access router when it boots up and is first configured. These commands are the same commands that could be given manually at the router's CLI interface; however, putting them in a configuration file avoids having to retype them whenever the router is reset.

Downloading the Configuration File

Usually, the Cisco IOS configuration file is specified as part of the DOCSIS configuration file. In this situation, the service provider creates and maintains both the DOCSIS and Cisco IOS configuration files for the routers, and those files are stored on TFTP servers located at the provider's headend plant.

The cable access router automatically loads the DOCSIS configuration file when first connected to a cable network and powered on. If the DOCSIS configuration file specifies that a Cisco IOS configuration file is to be loaded, the router uses the TFTP protocol to download that file and then executes the file so that the non-DOCSIS routing and interface parameters are correctly configured.

When the DOCSIS configuration file specifies that a Cisco IOS configuration file should be downloaded, the cable access router automatically takes the following steps to ensure that the configuration cannot be changed by the user at the remote site:

1. Ends all current Telnet sessions (if any).

2. Disables console access.

3. Deletes the current Cisco IOS configuration, if any.

4. Downloads the Cisco IOS configuration file.

5. After configuring itself according to the commands in the Cisco IOS configuration file, the router comes online and starts sending traffic.

If the DOCSIS configuration file does not specify that a Cisco IOS configuration file should be loaded, the network administrator can log in to the router's CLI interface and manually load the file using the copy tftp command. (In this situation, console access is not disabled, which allows users at the remote site to modify the configuration if desired.)

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Note The DOCSIS configuration file is a binary file that must be in the specific format given by the DOCSIS 1.0 specification; it configures DOCSIS and cable-related parameters. The Cisco IOS configuration file is a text file that can be in any arbitrary format, as long as the lines in that file contain valid commands that could be given at the router's CLI interface. Typically, the Cisco IOS configuration file sets routing parameters and whatever other parameters are needed for special feature sets, such as the firewall features.

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Startup and Run-Time Configuration Files

The startup configuration file is a Cisco IOS configuration file stored in the router's nonvolatile Flash memory and is automatically run whenever the router is reset or powered on. When a DOCSIS configuration file specifies that a Cisco IOS configuration file should be downloaded, that Cisco IOS configuration file automatically becomes the startup configuration file.

The run-time configuration file is the Cisco IOS configuration file that the router is currently using as it operates. When a router is first powered on or reset, the run-time configuration file is the same as the startup configuration file.

However, when you make configuration changes to the router, either by using the CLI or by using SNMP commands, the run-time configuration file is updated with those changes. Over time, the run-time configuration file has a different configuration than the startup configuration file. Resetting the router automatically erases the run-time configuration and restores the startup configuration.

If you want to save your changes to the router's configuration, you must save the run-time configuration as the startup configuration file. To do so, enter the following global configuration command:

copy running-config startup-config 

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Note Any changes you make to either the startup or run-time configuration are automatically overwritten when the router is rebooted, if the DOCSIS configuration file specifies that a new Cisco IOS configuration file must be downloaded from the TFTP server. If this is the case, you must also manually update the Cisco IOS configuration file on the TFTP server to preserve any configuration changes that you make.

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To restore the startup configuration without resetting the router, enter the following global configuration command:

copy startup-config running-config 

Displaying the Configuration Files

You can display the startup and run-time configuration files with the following global configuration commands:

show startup-config  
show running-config  

The cable access router displays the appropriate configuration file in a format that you can capture and save on a TFTP server so it can be downloaded to another router.

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Note The configuration files do not contain any commands that restore the router to its default values. For example, if you enable IP routing with the ip routing command, this is not saved in the configuration files because this is the default configuration. However, if you disable IP routing with the no ip routing command, this is saved in the configuration file.

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The show command uses exclamation marks (!) to create blank lines as spacers. These extra lines do not affect the functionality of the router; they exist only to make the configuration files more readable.

File Format

The Cisco IOS configuration file is an ASCII text file that contains any Cisco IOS configuration commands to configure the cable access router. The router is automatically put into the global configuration mode when the file is executed. But if you use commands for another command mode, you must give the appropriate global configuration command to enter that other command mode first.

For example, to configure the cable interface on the cable access router, you must first enter interface mode with the following command:

interface cable 0  

You can use exclamation marks (!) to create comments and blank lines in your own configuration files. These comments and blank lines are not preserved when the file is loaded into the router. However, they are useful for communicating information to other administrators who might be working with the files on the TFTP server.

Useful Commands

Table A-6 lists some of the most commonly-used commands for the cable access router.

Table A-6 Useful Commands 

Command	Command Mode	Purpose
banner	Global configuration	Displays and configures the login banners that appear when a user first logs in and when a user moves to a different command mode.
configure terminal	User EXEC	Enters global configuration mode.
copy startup-config running-config	Global configuration	Configures the router with its boot-up configuration file.
enable	User EXEC	Enters privileged EXEC mode.
exit	All modes	Leaves the current command mode and returns to the next higher level. If currently in user EXEC mode, logs you out of the router.
hostname	Global configuration	Sets the router's hostname.
logout	User EXEC	Logs out of user EXEC mode and the cable access router.
show flash	User EXEC	Displays the content of the router's Flash memory, which contains the Cisco IOS software image that was loaded.
show history	User EXEC	Displays the most recently-entered commands.
show interfaces	User EXEC	Displays the configuration and status of each of the router's interfaces.
show ip arp	User EXEC	Displays the contents of the router's current address resolution protocol (ARP) table.
show ip dhcp server statistics	User EXEC	Displays the contents of the router's DHCP database.
show ip interface	User EXEC	Displays the IP configuration and status for the router's Ethernet and cable interfaces.
show ip protocols	User EXEC	Displays the IP routing protocol parameters and status.
show ip rip database	User EXEC	Displays the contents of the Routing Information Protocol (RIP) database.
show ip route	User EXEC	Displays the contents of the router's current IP routing table.
show ip traffic	User EXEC	Displays statistics for the IP traffic sent through the router.
show protocols	User EXEC	Displays the currently-configured protocols for each interface.
show running-config	Privileged EXEC	Displays the active configuration.
show startup-config	Privileged EXEC	Displays the configuration loaded into the router at bootup.
show version	User EXEC	Displays the cable access router's software and hardware versions.