Cisco ASA 5500 Series Configuration Guide using the CLI, 8.4 and 8.6

Enabling ICMP Debugging Messages and Syslog Messages

Debugging messages and syslog messages can help you troubleshoot why your pings are not successful. The ASA only shows ICMP debugging messages for pings to the ASA interfaces, and not for pings through the ASA to other hosts. To enable debugging and syslog messages, perform the following steps:

	Command	Purpose
Step 1	debug icmp trace   hostname(config)# debug icmp trace	Shows ICMP packet information for pings to the ASA interfaces.
Step 2	logging monitor debug   hostname(config)# logging monitor debug	Sets syslog messages to be sent to Telnet or SSH sessions. Note You can alternately use the logging buffer debug command to send log messages to a buffer, and then view them later using the show logging command.
Step 3	terminal monitor   hostname(config)# terminal monitor	Sends the syslog messages to a Telnet or SSH session.
Step 4	logging on   hostname(config)# logging on	Enables syslog message generation.

To enable ICMP inspection to the default global policy, perform the following steps:

Examples

The following example shows a successful ping from an external host (209.165.201.2) to the ASA outside interface (209.165.201.1):

The output shows the ICMP packet length (32 bytes), the ICMP packet identifier (1), and the ICMP sequence number (the ICMP sequence number starts at 0, and is incremented each time that a request is sent).

Pinging ASA Interfaces

To test whether the ASA interfaces are up and running and that the ASA and connected routers are operating correctly, you can ping the ASA interfaces. To ping the ASA interfaces, perform the following steps:

Step 1 Draw a diagram of your single-mode ASA or security context that shows the interface names, security levels, and IP addresses.

Note Although this procedure uses IP addresses, the ping command also supports DNS names and names that are assigned to a local IP address with the name command.

The diagram should also include any directly connected routers and a host on the other side of the router from which you will ping the ASA. You will use this information in this procedure and in the procedure in the “Passing Traffic Through the ASA” section. (See Figure 82-1.)

Figure 82-1 Network Diagram with Interfaces, Routers, and Hosts

Step 2 Ping each ASA interface from the directly connected routers. For transparent mode, ping the management IP address. This test ensures that the ASA interfaces are active and that the interface configuration is correct.

A ping might fail if the ASA interface is not active, the interface configuration is incorrect, or if a switch between the ASA and a router is down (see Figure 82-2). In this case, no debug messages or syslog messages appear, because the packet never reaches the ASA.

Figure 82-2 Ping Failure at the ASA Interface

If the ping reaches the ASA, and it responds, debugging messages similar to the following appear:

If the ping reply does not return to the router, then a switch loop or redundant IP addresses may exist (see Figure 82-3).

Figure 82-3 Ping Failure Because of IP Addressing Problems

Step 3 Ping each ASA interface from a remote host. For transparent mode, ping the management IP address. This test checks whether the directly connected router can route the packet between the host and the ASA, and whether the ASA can correctly route the packet back to the host.

A ping might fail if the ASA does not have a return route to the host through the intermediate router (see Figure 82-4). In this case, the debugging messages show that the ping was successful, but syslog message 110001 appears, indicating a routing failure.

Figure 82-4 Ping Failure Because the Security Appliance has No Return Route

Passing Traffic Through the ASA

After you successfully ping the ASA interfaces, make sure that traffic can pass successfully through the ASA. For routed mode, this test shows that NAT is operating correctly, if configured. For transparent mode, which does not use NAT, this test confirms that the ASA is operating correctly. If the ping fails in transparent mode, contact the Cisco TAC.

To ping between hosts on different interfaces, perform the following steps:

	Command	Purpose
Step 1	access-list ICMPACL extended permit icmp any any   hostname(config)# access-list ICMPACL extended permit icmp any any	Adds an access list to allow ICMP traffic from any source host. Note By default, when hosts access a lower security interface, all traffic is allowed through. However, to access a higher security interface, you need the preceding access list.
Step 2	access-group ICMPACL in interface interface_name   hostname(config)# access-group ICMPACL in interface inside	Assigns the access list to each source interface. Repeat this command for each source interface.
Step 3	class-map ICMP-CLASS match access-list ICMPACL policy-map ICMP-POLICY class ICMP-CLASS inspect icmp service-policy ICMP-POLICY global   hostname(config)# class-map ICMP-CLASS hostname(config-cmap)# match access-list ICMPACL hostname(config)# policy-map ICMP-POLICY hostname(config-pmap)# class ICMP-CLASS hostname(config-pmap)# inspect icmp hostname(config)# service-policy ICMP-POLICY global	Enables the ICMP inspection engine and ensures that ICMP responses may return to the source host. For a host to access a lower security interface, you must enable ICMP inspection. However, to access a higher security interface, you must enable ICMP inspection and the preceding access list. Note Alternatively, you can also apply the ICMP access list to the destination interface to allow ICMP traffic back through the ASA.
Step 4	logging on   hostname(config)# logging on	Enables syslog message generation. If the ping succeeds, a syslog message appears to confirm the address translation for routed mode (305009 or 305011) and that an ICMP connection was established (302020). You can also enter either the show xlate or show conns command to view this information. If the ping fails for transparent mode, contact Cisco TAC. For routed mode, the ping might fail because NAT is not configured correctly (see Figure 82-5). In this case, a syslog message appears, showing that the NAT failed (305005 or 305006). If the ping is from an outside host to an inside host, and you do not have a static translation, the following syslog message appears: %ASA-3-106010: deny inbound icmp. Note The ASA only shows ICMP debugging messages for pings to the ASA interfaces, and not for pings through the ASA to other hosts.

Figure 82-5 Ping Failure Because the ASA is Not Translating Addresses

Disabling the Test Configuration

After you complete your testing, disable the test configuration that allows ICMP to and through the ASA and that prints debugging messages. If you leave this configuration in place, it can pose a serious security risk. Debugging messages also slow the ASA performance.

To disable the test configuration, perform the following steps:

Determining Packet Routing with Traceroute

You can trace the route of a packet using the traceroute feature, which is accessed with the traceroute command. A traceroute works by sending UDP packets to a destination on an invalid port. Because the port is not valid, the routers along the way to the destination respond with an ICMP Time Exceeded Message, and report that error to the ASA.

Tracing Packets with Packet Tracer

The packet tracer tool provides packet tracing for packet sniffing and network fault isolation, as well as detailed information about the packets and how they are processed by the ASA. If a configuration command did not cause the packet to drop, the packet tracer tool provides information about the cause in an easily readable manner.

In addition, you can trace the lifespan of a packet through the ASA to see whether the packet is operating correctly with the packet tracer tool. This tool enables you to do the following:

• Debug all packet drops in a production network.
• Verify the configuration is working as intended.
• Show all rules applicable to a packet, along with the CLI commands that caused the rule addition.
• Show a time line of packet changes in a data path.
• Inject tracer packets into the data path.
• Search for an IPv4 or IPv6 address based on the user identity and the FQDN.

To trace packets, enter the following command:

Handling TCP Packet Loss

To troubleshoot TCP packet loss, see the “Customizing the TCP Normalizer with a TCP Map” section for more information.

Recovering Passwords for the ASA

To recover passwords for the ASA, perform the following steps:

Step 1 Connect to the ASA console port according to the instructions in “Accessing the Appliance Command-Line Interface” section.

Step 2 Power off the ASA, and then power it on.

Step 3 After startup, press the Escape key when you are prompted to enter ROMMON mode.

Step 4 To update the configuration register value, enter the following command:

Step 5 To set the ASA to ignore the startup configuration, enter the following command:

The ASA displays the current configuration register value, and asks whether you want to change it:

Step 6 Record the current configuration register value, so you can restore it later.

Step 7 At the prompt, enter Y to change the value.

The ASA prompts you for new values.

Step 8 Accept the default values for all settings, except for the "disable system configuration?" value.

Step 9 At the prompt, enter Y.

Step 10 Reload the ASA by entering the following command:

The ASA loads the default configuration instead of the startup configuration.

Step 11 Access the privileged EXEC mode by entering the following command:

Step 12 When prompted for the password, press Enter.

The password is blank.

Step 13 Load the startup configuration by entering the following command:

Step 14 Access the global configuration mode by entering the following command:

Step 15 Change the passwords, as required, in the default configuration by entering the following commands:

Step 16 Load the default configuration by entering the following command:

The default configuration register value is 0x1. For more information about the configuration register, see the command reference.

Step 17 Save the new passwords to the startup configuration by entering the following command:

Disabling Password Recovery

To disable password recovery to ensure that unauthorized users cannot use the password recovery mechanism to compromise the ASA, enter the following command:

On the ASA, the no service password-recovery command prevents you from entering ROMMON mode with the configuration intact. When you enter ROMMON mode, the ASA prompts you to erase all Flash file systems. You cannot enter ROMMON mode without first performing this erasure. If you choose not to erase the Flash file system, the ASA reloads. Because password recovery depends on using ROMMON mode and maintaining the existing configuration, this erasure prevents you from recovering a password. However, disabling password recovery prevents unauthorized users from viewing the configuration or inserting different passwords. In this case, to restore the system to an operating state, load a new image and a backup configuration file, if available.

The service password-recovery command appears in the configuration file for information only. When you enter the command at the CLI prompt, the setting is saved in NVRAM. The only way to change the setting is to enter the command at the CLI prompt. Loading a new configuration with a different version of the command does not change the setting. If you disable password recovery when the ASA is configured to ignore the startup configuration at startup (in preparation for password recovery), then the ASA changes the setting to load the startup configuration as usual. If you use failover, and the standby unit is configured to ignore the startup configuration, then the same change is made to the configuration register when the no service password recovery command replicates to the standby unit.

Resetting the Password on the SSM Hardware Module

To reset the password to the default of “cisco” on the SSM hardware module, enter the following command:

Note Make sure that the SSM hardware module is in the Up state and supports password reset.

Command

Purpose

hw-module module 1 password-reset Reset the password on module in slot 1? [confirm] y hostname# y

Where 1 is the specified slot number on the SSM hardware module. Note On the AIP SSM, entering this command reboots the hardware module. The module is offline until the rebooting is finished. Enter the show module command to monitor the module status. The AIP SSM supports this command in version 6.0 and later. On the CSC SSM, entering this command resets web services on the hardware module after the password has been reset. You may lose connection to ASDM or be logged out of the hardware module. The CSC SSM supports this command in the most recent version of 6.3, dated January 2010, and later releases.

Viewing Debugging Messages

Because debugging output is assigned high priority in the CPU process, it can render the system unusable. For this reason, use debug commands only to troubleshoot specific problems or during troubleshooting sessions with Cisco TAC. Moreover, it is best to use debug commands during periods of less network traffic and fewer users. Debugging during these periods decreases the likelihood that increased debug command processing overhead will affect system use. To enable debugging messages, see the debug commands in the command reference.

Capturing Packets

Capturing packets is sometimes useful when troubleshooting connectivity problems or monitoring suspicious activity. We recommend that you contact the Cisco TAC if you want to use the packet capture feature. See the capture command in the command reference.

Viewing the Crash Dump

If the ASA crashes, you can view the crash dump information. We recommend contacting Cisco TAC if you want to interpret the crash dump. See the show crashdump command in the command reference.

Coredump

A coredump is a snapshot of the running program when the program has terminated abnormally, or crashed. Coredumps are used to diagnose or debug errors and save a crash for future off-site analysis. Cisco TAC may request that users enable the coredump feature to troubleshoot application or system crashes on the ASA. See the coredump command in the command reference.

Monitoring Per-Process CPU Usage

You can monitor the processes that run on the CPU. You can obtain information about the percentage of CPU that is used by a certain process. CPU usage statistics are sorted in descending order to display the highest consumer at the top. Also included is information about the load on the CPU per process, at 5 seconds, 1 minute, and 5 minutes before the log time. This information is updated automatically every 5 seconds to provide real-time statistics.You can use the show process cpu-usage sorted command to find a breakdown of the process-related load-to-CPU that is consumed by any configured contexts.