Cisco IOS Software and the EXEC Facility Fundamentals

Cisco IOS Software and the EXEC Facility Fundamentals
Cisco IOS Software Basic Skills

Getting Help

Accessing Different Command Modes

Undoing a Command or Feature

Saving Configuration Changes

Working with the EXEC Facility

Choosing a Method of Connecting to the Network

Permitting Users to Connect Directly to the Network

Connecting to the EXEC Facility

Where to Go Next

Cisco IOS Software and the EXEC Facility Fundamentals

If you are new to Cisco IOS software or need help understanding the EXEC facility and how it affects your network setup, you should read this chapter before starting configuration. Otherwise, proceed to Chapter 2, "Starting the AccessPath-TS3 System for the First Time."

Cisco IOS Software Basic Skills

This section describes what you need to know about the Cisco IOS software (the software that runs the Cisco AccessPath-TS3 Model 531 Integrated Access System) before you configure the AccessPath-TS3 system using the command-line interface (CLI). This section includes:

Understanding these concepts will expedite the configuration process. If you have never used the Cisco IOS software or need a refresher, take a few minutes to read this section before you proceed to the next section.

If you are already familiar with the Cisco IOS software, proceed to the section "Working with the EXEC Facility."

Getting Help

Use the question mark (?), Tab, and arrow keys to help you enter commands:

For a list of available commands, enter a question mark:

 
AS01> ?

To complete a command, enter the first few known characters followed by a Tab:

 
AS01> ena<Tab>

 
enable

For a list of command variables, enter the command followed by a space and a question mark:

 
AS01> show ?

To redisplay a command you previously entered, press the up arrow key. You can continue to press the up arrow key for more commands.
To display all the commands that start with a specific character or characters, enter the character(s) followed by a question mark (with no space):

 
AS01> e?

 
enable  end  endnode  exit

Note See the chapter "Configuring the User Interface" in the Configuration Fundamentals Configuration Guide for more information about any aspect of working with the user interface in the Cisco IOS software. The Configuration Fundamentals Configuration Guide is part of the Cisco IOS documentation in Cisco IOS Release 11.1 and later.

Accessing Different Command Modes

In addition to the EXEC facility, you can access several different command modes on AccessPath-TS3 system components. Each command mode permits you to configure different components. Table 1-1 lists the most common components and configuration modes.

You configure global parameters in global configuration mode, interface parameters in interface configuration mode, and line parameters in line configuration mode. For more information about using these configuration modes, see the Configuration Fundamentals Configuration Guide, which is part of the Cisco IOS documentation in Cisco IOS Release 11.1 and later.

Table 1-1 Common Command Modes

Command Mode	Access Method	Prompt	Exit Method
User EXEC	Log in.	AS01>	Use the logout or exit command.
Privileged EXEC	From user EXEC mode, enter the enable EXEC command.	AS01#	To exit back to user EXEC mode, use the disable command.
Global configuration	From privileged EXEC mode, enter the configure terminal command.	AS01(config)#	To exit to privileged EXEC mode, use the exit or end command or press Ctrl-Z.
Interface configuration	Enter the interface type number command, such as interface ethernet 0.	AS01(config-if)#	To exit to global configuration mode, use the exit command. To exit directly to privileged EXEC mode, use the end command or press Ctrl-Z.
Line configuration	Enter the line start-number end-number command, such as line 1 16.	AS01(config-line)#	To exit to global configuration mode, use the exit command. To exit directly to privileged EXEC mode, use the end command or press Ctrl-Z.
System configuration dialog	From privileged EXEC mode, enter the setup command.	Continue with config dialog?	To exit to privileged EXEC mode, press Ctrl-C.

Note You can press Ctrl-Z in any mode to immediately return to enable mode (AS01#), instead of entering exit, which returns you to the previous mode.

Undoing a Command or Feature

If you want to undo a command you entered or disable a feature, enter the keyword no before most commands; for example, no ip routing.

Saving Configuration Changes

You need to enter the copy running-config startup-config command to save your configuration changes to nonvolatile random-access memory (NVRAM) so that they will not be lost if there is a system reload or power outage. For example:

 
AS01# copy running-config startup-config

 
Building configuration...

It might take a minute or two to save the configuration to NVRAM. After the configuration has been saved, the following appears:

 
[OK]

 
AS01#

Proceed to the next section, "Working with the EXEC Facility," for additional information you will need before configuring the AccessPath-TS3 system.

Working with the EXEC Facility

This section introduces the EXEC facility, which you will use to configure your AccessPath-TS3 system.

Choosing a Method of Connecting to the Network

The prompt that appears when you first log in to any AccessPath-TS3 System Shelf is called the EXEC prompt. When you access the EXEC prompt, you are accessing the EXEC facility and starting an EXEC session. You can log in through the following ports on an Access Server :

Console port
LAN or WAN interface
Asynchronous interface

This section discusses how to configure the Access Servers to permit remote clients to dial in and gain access to network resources (such as printers and file servers).

You can enable remote clients to dial in and access network resources in two ways:

Have them access the EXEC facility and then access network resources via the EXEC session
Have them connect directly to the network and bypass the EXEC facility

In general, you should give system administrators access to the EXEC facility, but give dial-in clients access only to the network. The next section, "Permitting Users to Connect Directly to the Network," describes how to enable users to log in to the network without ever seeing the Access Server .

Permitting Users to Connect Directly to the Network

When a user dials in to the AccessPath-TS3 system, the Cisco IOS software running on the Access Server can detect the incoming protocol automatically if you configure it to autoselect the protocol. To autoselect the Point-to-Point Protocol (PPP), issue two commands: the async mode interactive asynchronous interface configuration command and the autoselect ppp line configuration command. After you have issued these commands, if the Cisco IOS software detects that the remote device is using PPP, it can negotiate PPP sessions automatically.

Caution Autoselect bypasses security dialogs for users who log in to an EXEC session on the AccessPath-TS3 system. If you configure a line to detect PPP automatically, Cisco recommends that you use Challenge Handshake Authentication Protocol (CHAP) authentication. For complete security information, see Chapter 5, "Configuring Security for the AccessPath-TS3 System."

Figure 1-1 shows the authentication process when autoselect is used.

Figure 1-1 Flowchart of EXEC Facility and Autoselect Authentication Options

Timesaver If you issue the autoselect ppp line configuration command, you must first issue the async mode interactive asynchronous interface configuration command. The async mode interactive command enables the interface to select a protocol type dynamically. If you do not enter the async mode interactive command before you issue the autoselect ppp command, the following warning message appears: "%Autoselect w/o the interface command `Async mode interactive' is useless." See Chapter 8, "Configuring Multichassis Multilink PPP," for more information.

Figure 1-2 shows an example of what clients see when they connect to the network using PPP.

Figure 1-2 Client Connection to an IP Network Using Windows 95 PPP Application

After clients using PPP connect to the network, they have access to all IP network resources, such as UNIX hosts for Telnet or FTP sessions, other PCs on the network, or Windows NT servers.

Connecting to the EXEC Facility

If you permit users to dial in to the EXEC facility, they can use terminal services (such as Telnet), run an asynchronous protocol over the line, or use one of many other access services. For example, users who are permitted to dial in to the EXEC facility can enter the ppp command to initiate a PPP session with a device on the network.

To enable users to log in to the EXEC facility, issue the autoselect during-login line configuration command. When Cisco IOS software detects a carriage return, the user is connected to the EXEC facility. You also access the EXEC facility any time you log in to and configure the AccessPath-TS3 system through the System Controller.

There are two primary levels to the EXEC facility:

User-level EXEC mode, which is what you see when you first log in to an Access Server , whether from a remote client, or through a console port connection:

 
AS01>

Privileged-level EXEC mode, which provides access to configuration mode. To enter privileged-level EXEC mode, issue the enable command, enter the enable password, and press Return, as shown in the following example:

 
AS01> enable 

 
Password: <password>

 
AS01# 

AccessPath-TS3 system network administrators should protect privileged level EXEC mode with a password that only network administrators know. This gives users access only to the user-level EXEC mode so that they can issue commands to connect with other network devices (such as the ppp command) and prevents them from changing the configuration of the AccessPath-TS3 system.

For an overview of configuration mode, see the section, "Accessing Different Command Modes." For information about configuring security, see Chapter 5, "Configuring Security for the AccessPath-TS3 System."

Where to Go Next

Now that you have learned some Cisco IOS and EXEC facility software basics, you are ready to configure the AccessPath-TS3 system using the CLI.

Remember that:

You can use the question mark (?), Tab, and arrow keys to help you enter commands.
Each command mode restricts you to a set of commands. If you are having difficulty entering a command, check the prompt and then enter the question mark (?) for a list of available commands. You might be in the wrong command mode or using the wrong syntax.
If you want to disable a feature, enter the keyword no before the command; for example, no ip routing.
You need to save your configuration changes to NVRAM so that they will not be lost if there is a system reload or power outage. Any of the following commands will do this: write, write memory, or write running-config startup-config.

Table of Contents

Cisco IOS Software and the EXEC Facility Fundamentals

Cisco IOS Software Basic Skills

Getting Help

Accessing Different Command Modes

Undoing a Command or Feature

Saving Configuration Changes

Working with the EXEC Facility

Choosing a Method of Connecting to the Network

Permitting Users to Connect Directly to the Network

Connecting to the EXEC Facility

Where to Go Next