Accessing the Cisco ASA Appliances
Cisco ASA provides two types of user interface:
- Command-line interface (CLI)
- Graphical user interface (GUI)
The CLI provides nongraphical access to the Cisco ASA. The CLI can be accessed from a console, Telnet, or Secure Shell (SSH) session. Telnet and SSH are discussed later in the chapter, in the "Remote System Management" Section. The security appliance can also use Adaptive Security Device Manager (ASDM), a GUI-based application to configure the different security and networking features. ASDM is discussed in later chapters within Part V, "Adaptive Security Device Manager."
Establishing a Console Connection
A new security appliance, by default, has no IP addresses assigned to its interfaces. To access the CLI, you need to have a successful connection to the console port of the security appliance. The console port is a serial asynchronous port with the settings listed in Table 4-1.
|
Parameters |
Value |
|---|---|
|
Baud rate |
9600 |
|
Data bits |
8 |
|
Parity |
None |
|
Stop bits |
1 |
|
Flow control |
Hardware |
The console port on the security appliance can be connected to a serial port on a PC using a flat rolled console cable, with a DB9 serial adapter on one end and a RJ-45 port on the other. The DB9 side of the cable goes to the serial port of a PC, while the RJ-45 end of the cable goes to the console port of the security appliance, as illustrated in Figure 4-1.
Figure 4-1. Console Port Connectivity from a Computer
After connecting the console cable to the security appliance and the computer, launch terminal-emulation software, such as HyperTerminal or TeraTerm, to send and receive output. You can launch HyperTerminal by navigating to Start > Programs > Accessories > Communications > HyperTerminal on a Windows-based PC. The initial configuration window of HyperTerminal is shown in Figure 4-2. In the Connection Description dialog box, you can enter a connection name to identify this session as a unique connection. A connection name of Console Connection to the Cisco ASA is specified in Figure 4-2. You can choose an icon to associate with the connection entry. After filling out the connection name and selecting an icon, click OK to proceed to the Connect To window.
Figure 4-2. Initial Configuration of HyperTerminal
Specify the connection type in the Connect To window. Because the console port uses an asynchronous serial connection, the HyperTerminal setting must use a COM port. As illustrated in Figure 4-3, COM3 is being set up for the serial connection to the security appliance. After you are done, click OK to proceed to the last configuration window.
Figure 4-3. Setting HyperTerminal Connection Type
The next window is used to configure port properties, such as the baud rate and flow control. Figure 4-4 shows HyperTerminal set up with the values listed in Table 4-1. After configuring the port settings, click OK to complete the configuration setup.
Figure 4-4. Setting HyperTerminal Port Specification
The HyperTerminal application is ready to transmit and receive data from the security appliance. If you press Enter a few times, you should see a ciscoasa> prompt in the HyperTerminal window, as shown in Figure 4-5.
Figure 4-5. Initial Command Prompt in HyperTerminal
The next section describes how to use the CLI after establishing a successful console connection.
Command-Line Interface
After a successful console connection, the security appliance is ready to accept your commands. The Cisco ASA contains a similar command set structure as a Cisco IOS router and offers the following access modes:
- User mode, also known as user access mode
- Privileged mode
- Configuration mode
- Sub-configuration mode
- ROMMON mode
User mode, shown as the hostname with a > sign, is the first mode of access available when you log into the security appliance. This mode offers a limited set of commands that is useful in obtaining basic information about the security appliance. One of the important commands in this mode is enable, which prompts a user to specify a password to log into privileged mode.
Privileged mode, shown as the host name with a # sign, gives full access to a user after a successful logon. This mode also allows execution of all the commands that are available in user mode. The security appliance offers a rich set of monitoring and troubleshooting commands to check the health of different processes and features in the security appliance. One of the important commands in this mode is configure terminal, which places a user in configuration mode.
Note
The security appliance enables you to restrict what a user can do by implementing command authorization. This is covered in Chapter 7, "Authentication, Authorization, and Accounting (AAA)."
Configuration mode, displayed as the host name with a (config)# prompt, allows a user to enable or disable a feature, set up security and networking components, and tweak the default parameters. This mode not only allows the user to configure the security appliance, but also allows the use of all the commands that are available in the user and privileged modes. A user may enter into the sub-configuration mode of different features from this mode.
Sub-configuration mode, displayed as the hostname with a (config-xxxx)# prompt, lets a user configure specific networking or security features on the security appliance. The xxxx is replaced by the process/feature keyword that is being configured on the security appliance. For example, if a user is setting up specific parameters on an interface, the prompt changes to (config-if). Sub-configuration mode allows the user to execute all the configuration mode commands as well as the user and privileged mode commands.
In Example 4-1, a user logs into privileged mode from user access mode by typing the enable command. The security appliance prompts a user to specify a password to gain privileged mode access. If the security appliance has the default configuration, it uses a null (no) password to grant access. After logging into privileged mode, the user types configure terminal to access configuration mode. The user enters into interface subconfiguration mode by typing the interface GigabitEthernet0/0 command. To go back to the previous mode, the user can enter exit or quit, as shown in Example 4-1.
Example 4-1. Accessing the Privileged and Configuration Modes
ciscoasa> enable Password: ciscoasa# configure terminal ciscoasa(config)# interface GigabitEthernet0/0 ciscoasa(config-if)# exit ciscoasa(config)# exit ciscoasa#
In the preceding example, the administrator of the security appliance typed exit twice to return to the privileged mode prompt. Optionally, you can type end to return to privileged mode from any configuration mode.
Tip
Like a Cisco IOS router, the security appliance also allows you to press the Tab key to complete a partial command. For example, to enter a show command, type sho and press the Tab key. The security appliance displays the complete show command on the screen.
The security appliance allows you to abbreviate commands and keywords to the number of characters that identify a distinct abbreviation. For example, you can abbreviate the enable command as en.
All the supported options and arguments of a command are displayed when you type ? after the command. For example, you can type show ? to see all the options that are supported under the show command.
The security appliance also provides a brief description and command syntax when you type help followed by the command. For example, when you type help reload, the security appliance shows the command syntax for reload, a description, and the supported arguments.
The security appliance uses ROMMON mode (Read-Only-Memory Monitor mode) when it does not find a bootable image or when an administrator forces it to enter into that mode. In ROMMON mode, you can use a TFTP server to load a system image into the security appliance. ROMMON mode is also used to recover the system password, discussed later in this chapter under "Image Recovery Using ROMMON."