4.0 CCNA - IP Services

4.5 Syslog Features and Configuration

Syslog configuration

Configuring syslog on a Cisco IOS device (example configuration):

Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# logging host 10.0.0.1
Router(config)# logging trap warnings
Router(config)# end
Router#

In this example, the syslog server is configured to receive log messages from the router at IP address 10.0.0.1. The logging trap warnings command specifies that only warning, error, critical, alert, and emergency messages should be sent to the syslog server.

Once the configuration is complete, you can verify the syslog configuration by using the following command:

Verification:

Router# show logging
Syslog logging: enabled (0 messages dropped, 0 messages rate-limited, 0 flushes, 0 overruns)
No Active Message Discriminator.

No Inactive Message Discriminator.

Console logging: level debugging, 0 messages logged, xml disabled,
             filtering disabled
Monitor logging: level debugging, 0 messages logged, xml disabled,
             filtering disabled
Buffer logging: level debugging, 0 messages logged, xml disabled,
             filtering disabled
Logging Exception size (4096 bytes)
Count and timestamp logging messages: disabled
Persistent logging: disabled
No active filter modules.
ESM: 0 messages dropped
Trap logging: level warnings, xml disabled,
             Filter logging: disabled
Logging to 10.0.0.1 (udp port 514, audit disabled,
             link up),
             0 messages logged,
             xml disabled, sequence number disabled,
             filtering disabled

Router#

This output confirms that syslog logging is enabled, and that the syslog server is set to receive warning, error, critical, alert, and emergency messages. The show logging command also displays information about the status of other logging facilities, such as console logging, buffer logging, and trap logging.

Monitor, Console, and Buffer logging

Monitor, Console, and Buffer logging are three different types of logging in Cisco IOS devices.

1. Monitor logging: The monitor logging facility sends log messages to a terminal line interface on the device. These messages can be used for debugging purposes or to provide real-time information about the device's activities.

2. Console logging: The console logging facility sends log messages to the console line interface of the device. This facility is useful for capturing messages that are generated during the initial configuration and startup of the device, or for debugging connectivity issues.

3. Buffer logging: The buffer logging facility stores log messages in a memory buffer on the device. This facility is useful for storing log messages that would otherwise be lost if the device experiences a crash or other issue. The log messages can be viewed later by using the show logging command.

Each of these logging facilities provides a different type of information that can be used to monitor and troubleshoot network devices. By configuring logging to multiple facilities, administrators can obtain a comprehensive view of the device's activities, which can be useful for resolving issues and optimizing network performance.

Troubleshooting using syslog

Syslog is a powerful tool that can be used for troubleshooting network issues. Here are some steps you can take to troubleshoot using syslog:

1. Identify the source of the issue: Before you can begin troubleshooting, you need to identify the source of the issue. This may be a device, a service, or an application that is experiencing problems.

2. Check the syslog messages: Once you have identified the source of the issue, you can check the syslog messages on the relevant devices to see if they contain any information that can help you diagnose the problem. To do this, you can use the show logging command on the devices to view the log messages.

3. Search for keywords: If you have a lot of log messages to go through, you can use the pipe (|) and the include (| include) command to search for specific keywords that may be related to the issue. For example, if you are having issues with a specific service, you can search for log messages that contain the name of that service.

4. Analyze the syslog messages: Once you have found the relevant log messages, you need to analyze them to determine the root cause of the issue. This may involve looking for patterns in the messages, comparing messages from different devices, or cross-referencing the messages with other information you have about the network.

5. Resolve the issue: Once you have identified the root cause of the issue, you can take steps to resolve it. This may involve making configuration changes, restarting services, or replacing faulty hardware.

Syslog can be a valuable tool for network administrators, as it provides detailed information about the activities of network devices, and can help you resolve issues more quickly.