Synchronous Logging Cisco

8 min read Oct 11, 2024

Synchronous Logging in Cisco Devices: A Comprehensive Guide

In the realm of network management, synchronous logging plays a crucial role in providing real-time insights into network events. This powerful feature allows Cisco devices to forward logs to a central logging server, ensuring that critical information is readily available for analysis and troubleshooting. Understanding synchronous logging is paramount for network administrators seeking to maintain a secure and efficient network infrastructure.

Why Synchronous Logging?

Traditionally, Cisco devices relied on asynchronous logging, where log messages were buffered locally and sent periodically to a logging server. However, this approach presented several limitations:

Delayed Logging: Asynchronous logging could introduce significant delays in receiving log messages, making it difficult to track and respond to events in a timely manner.
Log Loss: In scenarios with high network traffic or device overload, log messages might be dropped or lost during transmission, resulting in incomplete event records.
Limited Visibility: Asynchronous logging hindered real-time visibility into network events, potentially delaying troubleshooting and incident resolution.

Synchronous logging addresses these drawbacks by enabling the immediate forwarding of log messages to a designated logging server. This real-time approach offers numerous advantages:

Real-time Visibility: With synchronous logging, network administrators can access log messages in real-time, providing instant insights into network events as they occur.
Improved Troubleshooting: The availability of immediate log data empowers network administrators to quickly pinpoint the root cause of issues, leading to faster troubleshooting and resolution.
Enhanced Security Monitoring: Real-time log access enhances security monitoring by promptly revealing suspicious activities, enabling prompt intervention and mitigating potential threats.

How Synchronous Logging Works

Synchronous logging relies on a simple yet effective mechanism. When a log message is generated on a Cisco device, it is immediately sent to the designated logging server. This process occurs in real-time, without buffering or delay, ensuring immediate delivery.

Key Components:

Logging Server: A dedicated server responsible for receiving and storing log messages from Cisco devices.
Logging Facility: A configuration parameter on the Cisco device that specifies the destination for log messages.
Logging Level: A configuration parameter that controls the severity level of log messages to be sent to the logging server.
Logging Transport Protocol: The network protocol used to transmit log messages (e.g., UDP, TCP).

Configuring Synchronous Logging

Configuring synchronous logging is straightforward and can be achieved through the Cisco IOS command-line interface (CLI).

Steps:

Configure the logging server:
```
logging host 
```
Replace <server IP address> with the actual IP address of your logging server.
Specify the logging facility:
```
logging facility 
```
<facility level> specifies the severity levels of log messages to be forwarded. Common facilities include:
- local0-local7: User-defined logging facilities.
- auth: Authentication-related messages.
- daemon: System daemon messages.
- kern: Kernel messages.
- mail: Mail system messages.
- syslog: General system messages.
- user: User-level messages.
Set the logging level:
```
logging 
```
<severity level> determines the severity of log messages to be forwarded. Common levels include:
- emergency: Critical system failure.
- alert: Immediate action required.
- critical: Serious system errors.
- error: Non-critical errors.
- warning: Potential problems or warnings.
- notice: Informational messages.
- info: General informational messages.
- debug: Detailed debugging information.
Choose the logging transport protocol:
```
logging transport 
```
<protocol> can be either udp or tcp. UDP is generally preferred for its lightweight nature, while TCP provides reliable delivery.

Example:

logging host 192.168.1.100
logging facility local0-local7
logging level 7
logging transport udp

This configuration sends all log messages from the device to the logging server with the IP address 192.168.1.100, using UDP as the transport protocol.

Best Practices for Synchronous Logging

Configure Logging Server: Ensure that the logging server is properly configured to receive and store log messages from Cisco devices.
Secure Logging: Implement security measures to protect the logging server from unauthorized access.
Log Rotation: Configure log rotation to manage storage space on the logging server, preventing it from becoming overwhelmed.
Monitor Log Data: Regularly review and analyze log data to identify trends, potential issues, and security events.
Test and Validate: After configuring synchronous logging, thoroughly test the setup to ensure that log messages are being received correctly on the logging server.

Conclusion

Synchronous logging is an essential feature for network administrators seeking real-time visibility into network events. By enabling immediate log forwarding to a central server, it provides valuable insights for troubleshooting, security monitoring, and overall network management. Proper configuration and best practices ensure that synchronous logging effectively serves its purpose, enhancing network performance and security.