4.5 - Syslog Features and How to Use Them

Greetings, Tech Talkers!

This is Tor, your trusted network engineering uplink! Today, we're exploring the world of Syslog, a vital tool for network monitoring and troubleshooting. Syslog provides a standardized way for devices to send event messages, making it easier to track and analyze what's happening across your network.

In this article, we'll delve into what Syslog is, how it works, and how to configure it on Cisco devices. By the end, you'll understand how to harness Syslog to keep your network running smoothly and efficiently.

Let's get started!

What is Syslog?

Syslog is a protocol used for logging system messages and events from network devices. It allows devices like routers, switches, servers, and firewalls to send log messages to a central server, known as a Syslog server or Syslog collector.

Key Features of Syslog:

• Centralized Logging: Collects logs from multiple devices in one place.

• Standardization: Provides a consistent format for log messages.

• Severity Levels: Categorizes messages based on importance.

• Facility Codes: Identifies the source of the log message within the system.

Syslog Message Format

A typical Syslog message includes:

1. Timestamp: Indicates when the event occurred.

2. Hostname or IP Address: Identifies the source device.

3. Facility Code: Denotes the type of process that generated the message.

4. Severity Level: Indicates the importance of the message.

5. Message Content: Describes the event or issue.

Syslog Severity Levels

Syslog messages are assigned severity levels ranging from 0 to 7:

Configuring Syslog on Cisco Devices

Example Scenario:

• Configure a Cisco router to send Syslog messages to a Syslog server at IP address `192.0.2.100`.

Configuration Steps:

1. Specify the Syslog Server:

Router(config)# logging host 192.0.2.100

2. Set the Logging Trap Level:

   1. Determines the severity level of messages sent to the Syslog server.

  Router(config)# logging trap [level]

Example:

Router(config)# logging trap informational

This will send messages with severity levels 0 to 6.

3. Include Timestamps in Logs (Recommended):

Router(config)# service timestamps log datetime msec

Adds date and time to log messages.

4. Include Sequence Numbers (Optional):

Router(config)# service sequence-numbers

Adds sequence numbers to log messages for easier tracking.

5. Log Messages to Internal Buffer (Optional):

Router(config)# logging buffered [size] [level]

Example:

Router(config)# logging buffered 8192 informational

Stores log messages in the router's RAM for later viewing.

Configuring Syslog Server

To collect and analyze Syslog messages, you'll need a Syslog server. Popular options include:

• Syslog-ng

• rsyslog

• SolarWinds Kiwi Syslog Server

• Graylog

Basic Steps:

1. Install Syslog Server Software:

• Choose a Syslog server that meets your needs and install it on a server machine.

2. Configure the Syslog Server to Receive Logs:

• Ensure it's set up to listen for incoming Syslog messages (usually on UDP port 514).

3. Set Up Log Rotation and Archiving (Optional):

• Implement log rotation to manage disk space.

4. Secure the Syslog Server:

• Restrict access to authorized personnel.

• Implement firewalls and access control lists.

Viewing Syslog Messages on the Router

To view stored log messages on the router:

Router# show logging

This command displays the contents of the logging buffer.

Filtering Logs by Severity

You can adjust which messages are displayed on the console or terminal:

• Console Logging:

Router(config)# logging console [level]

• Terminal Logging (When Using Telnet/SSH):

Router(config)# logging monitor [level]

Example:

Router(config)# logging console warnings

Only messages with severity levels 0 to 4 will be displayed on the console.

Best Practices

• Set Appropriate Severity Levels:

• Avoid overwhelming the Syslog server with unnecessary messages.

• Synchronize Time Across Devices:

• Use NTP to ensure accurate timestamps.

• Secure Syslog Communications:

• Consider using Secure Syslog (e.g., Syslog over TLS) for sensitive environments.

• Monitor and Analyze Logs Regularly:

• Use tools to analyze logs for trends or issues.

• Implement Log Rotation and Archiving:

• Manage disk space and comply with data retention policies.

Troubleshooting Syslog

Common Issues:

• No Logs Received by Syslog Server:

  • Verify network connectivity between devices and server.

  • Ensure firewalls are not blocking UDP port 514.

Incorrect Timestamps:

• Check time settings and NTP configuration on devices.

Overwhelming Log Volume:

• Adjust logging levels to reduce unnecessary messages.

Useful Commands:

• `show logging`

• `show logging history`

• `debug logging` *(Use with caution.)*

Wrapping It Up

Syslog is an indispensable tool for network administrators, providing insights into the health and performance of network devices. By effectively configuring and utilizing Syslog, you can proactively identify and resolve issues, ensuring your network operates smoothly.

Until next time, Tech Talkers, keep your logs centralized and your networks optimized!

Thanks,

Tor – Your trusted network engineering uplink