Remote Management Access to ASA and FWSM
The examples presented so far have considered that there was physical access to the console port of the appliance (or to the hosting Catalyst 6500 for the FWSM). This section examines management connections that rely on remote access protocols (Telnet, SSH, and HTTPS).
Telnet is a classic terminal access protocol that has received much criticism because of its clear text nature. It is highly recommended you replace it with SSH, which provides confidentiality.
At any rate, Telnet can still be useful for testing purposes mainly during initial setup. The commands shown in Example 3-15 specify the following:
- Telnet access is accepted only when it is initiated from source addresses on network 192.168.1.0/24. Further, the packets must arrive through the logical interface called mgmt.
- The authentication of users who have permission to Telnet to the firewall is done using the LOCAL database. (LOCAL is a reserved keyword for ASA and FWSM.)
- The username admin is included in the LOCAL database.
Example 3-15 also displays a sample Telnet session coming from address 192.168.1.201.
Example 3-15. Configuring and Verifying Telnet Access
! Creating a local user username admin password cisco123 privilege 15 ! ! Telnet access is authenticated using the LOCAL Data Base aaa authentication telnet console LOCAL ! ! Defining source addresses that can initiate Telnet Access to the Firewall telnet 192.168.1.0 255.255.255.0 mgmt ! ! Initiating a Telnet session to ASA DMZ# telnet 192.168.1.2 Trying 192.168.1.2 ... Open User Access Verification Username:admin Password: ******** Type help or '?' for a list of available commands. ASA5505>enable Password: ***** ASA5505# ! ! Displaying connections to the Firewall ASA5505# show conn all | include Identity TCP mgmt 192.168.1.201:35313 NP Identity Ifc 192.168.1.2:23, idle 0:00:00, bytes 1017, flags UOB ! ASA5505# who 0: 192.168.1.201
If remote CLI access to the firewalls is needed, SSH is the protocol of choice. It provides the same terminal services that Telnet does but with the significant advantage of encrypting traffic between client and server (the firewall receiving the connection).
Because SSH uses RSA public keys to encrypt the sessions, you need to have consistent timing information. Example 3-16 shows not only how to manually adjust and verify timing information, but also how to create a domain name and generate RSA keys.
Example 3-17 shows how to visualize SSH-related information in the Running-config. Notice that the default timeout value for SSH sessions is 5 minutes.
Example 3-16. Recommended Tasks Before Starting SSH Configuration
! Setting Local Time (before generating the cryptographic keys) ASA5505# clock set 19:05:00 november 15 2009 ! ! Verifying Time Information ASA5505# show running-config clock clock timezone BRT -3 ! ASA5505# show clock detail 19:18:00.569 BRT Sun Nov 15 2009 Time source is user configuration ! ! Configuring a domain-name ASA5505(config)# domain-name mylab.lab ! ! Removing (if needed) any previously generated RSA keys ASA5505(config)# crypto key zeroize rsa WARNING: All RSA keys will be removed. WARNING: All device digital certificates issued using these keys will also be removed. Do you really want to remove these keys? [yes/no]: yes ! ! Generating new RSA Cryptographic Keys ASA5505(config)# crypto key generate rsa modulus 1024 INFO: The name for the keys will be: <Default-RSA-Key> Keypair generation process begin. Please wait... ! ! Displaying the RSA Public Keys ASA5505# show crypto key mypubkey rsa Key pair was generated at: 19:24:29 BRT Nov 15 2009 Key name: <Default-RSA-Key> Usage: General Purpose Key Modulus Size (bits): 1024 Key Data: 30819f30 0d06092a 864886f7 0d010101 05000381 8d003081 89028181 008e60c4 bce3e63a 47aa12c4 e78c0a76 f2faf41c 5d8d461a 4978a5f6 0a4ac11b 26585f61 d6b5adcb f5ce2430 a96c6fb9 d09f2187 3525255a 349e015e 37d0dd79 90e2b2f1 5e968993 b9bb9cde 557ba395 e0b20f7c 0049b0d8 5d901902 fe8269ce 74f06a7f 16713eea 8fe2a0a8 9ddeb2c3 1d258249 d16e6fc4 5a3b4fb6 be977bbf 55020301 0001
Example 3-17. SSH Configuration
ASA5505# show running-config | include ssh aaa authentication ssh console LOCAL ssh 192.168.1.0 255.255.255.0 mgmt ssh timeout 5
HTTPS Access Using ASDM
The Adaptive Security Device Manager (ASDM) is an intuitive and easy-to-use GUI that accompanies every member of the ASA family. The interface provides a nice graphical abstraction for the actual commands that are used not only to implement the features but also to verify their operation, thus allowing users who are already familiar with classic firewall concepts (even from other vendors) to easily adapt their knowledge to the new GUI and immediately start working.
Documenting ASDM usage with its uncountable configuration and monitoring screens is beyond the scope of this book. However, the preparation of firewall devices to accommodate ASDM management is covered.
ASDM uses the HTTPS protocol for communications between the management station and the firewall. After properly loading the ASDM image on the device's flash memory, a web browser can be employed for the first access to the device, with the underlying goal of installing the ASDM launcher application on the administrator's PC.
Example 3-18 shows the preliminary tasks for enabling HTTPS access and assumes that the remote user has been granted the highest privilege level (priv-lvl = 15) and that the requests arrive though the logical interface called mgmt. In the example, the user named admin is authenticated against the LOCAL database and should start the management session from a host that belongs to the 192.168.1.0/24 subnet. The example also contains information about location of the ASDM image in the device flash (disk0: in this case) and how to find it within the show version output.
Example 3-18. Enabling HTTPS Access on ASA
! Assigning the highest privilege level (15) to the HTTPS user usernameadmin password ****** privilege 15 ! ! Defining allowed source IP Addresses. Authentication using the LOCAL Data Base http 192.168.1.0 255.255.255.0 mgmt aaa authentication http consoleLOCAL ! ! Enabling the HTTPS server http server enable ! ! Defining the location of the ASDM image asdm image disk0:/asdm-621.bin ! ! Verifying Operating System and ASDM versions ASA5505# show version | include Version Cisco Adaptive Security Appliance Software Version 8.2(1) Device Manager Version 6.2(1)
Figure 3-4 portrays the web browser access to the HTPPS server on the device whose management interface is configured with the address 192.168.1.2 (https://192.168.1.2).
Figure 3-4 First HTTPS Access and Initial ASDM Page
From this screen, select the Install ASDM Launcher and Run ASDM option and follow these steps:
- Step 1. Authenticate with the credentials configured in Example 3-18 when the Connect to 192.168.1.2 window displays.
- Step 2. From the File Download - Security Warning window, save the ".msi" file locally.
- Step 3. Run the ".msi" file and install the ASDM Launcher application.
- Step 4. After starting the ASDM Launcher, fill in the IP address (192.168.1.2 in this case) and the credentials (username/password).
- Step 5. After accepting the device certificate, the main ASDM page displays (Figure 3-5). This screen summarizes information for the device, including available licenses, interface status, and system resources status.
Figure 3-5 ASDM Home Page - Device Dashboard
Figure 3-6 depicts the base ASDM screen for Interface Configuration on an ASA 5505 appliance. Notice that the full path to this particular screen, Configuration > Device Setup> Interfaces, displays on the top of the right pane.
Figure 3-6 Base ASDM Page for Interface Configuration
Figure 3-7 shows a sample ASDM screen that helps perform the Monitoring task of verifying the ARP table. The complete path for viewing this table is represented at the top of the right pane (Monitoring > Interfaces > ARP Table).
Figure 3-7 Base ASDM Page for ARP Table Monitoring