Configuring Syslog on Cisco Routers

Syslog is a protocol used by network devices and other systems to send log messages to a central logging server. Cisco routers and switches can be configured to send their log messages to a syslog server, which helps network administrators monitor and troubleshoot their networks more effectively.

What is Syslog?

Syslog is a standard protocol defined in RFC 3164 that allows devices to send log messages across IP networks. These messages contain information about system events, errors, warnings, and other important notifications. The protocol uses UDP port 514 by default.

Syslog Severity Levels

Syslog uses eight severity levels to categorize messages:

• 0 - Emergency: System is unusable
• 1 - Alert: Action must be taken immediately
• 2 - Critical: Critical conditions
• 3 - Error: Error conditions
• 4 - Warning: Warning conditions
• 5 - Notice: Normal but significant condition
• 6 - Informational: Informational messages
• 7 - Debug: Debug-level messages

Basic Syslog Configuration

To configure a Cisco router to send syslog messages to a remote server, use the following commands:

Router(config)# logging host 192.168.1.100
Router(config)# logging trap informational
Router(config)# logging facility local0
Router(config)# logging source-interface loopback0

Let's break down each command:

• logging host 192.168.1.100 - Specifies the IP address of the syslog server
• logging trap informational - Sets the severity level for messages sent to the syslog server
• logging facility local0 - Sets the syslog facility code
• logging source-interface loopback0 - Specifies the source interface for syslog messages

Additional Configuration Options

You can also configure the following additional options:

Enable Logging

Router(config)# logging on

Set Buffer Size

Router(config)# logging buffered 8192

Configure Console Logging

Router(config)# logging console warnings

Configure Terminal Logging

Router(config)# logging monitor debugging

Verifying Syslog Configuration

To verify your syslog configuration, use the following show commands:

Router# show logging
Router# show logging history

The show logging command displays the current logging configuration and recent log messages stored in the router's buffer.

Testing Syslog

You can test your syslog configuration by generating a test message:

Router# send log "This is a test syslog message"

This command sends a test message to all configured logging destinations.

Best Practices

• Use a dedicated management network for syslog traffic when possible
• Configure appropriate severity levels to avoid overwhelming the syslog server
• Use NTP to synchronize time between devices for accurate log timestamps
• Configure multiple syslog servers for redundancy
• Regularly review and analyze syslog messages for network health and security

Conclusion

Configuring syslog on Cisco routers is essential for effective network monitoring and troubleshooting. By centralizing log messages on a syslog server, network administrators can more easily track events, identify problems, and maintain network security. Remember to configure appropriate severity levels and use best practices to ensure your logging system provides valuable insights without overwhelming your infrastructure.