How To Enable Full Logging For Named/Bind/DNS Service?

Modifying the named.conf File

The named.conf file is usually in the /etc/named/ or /etc/bind/ directory, based on your system. To set up full logging, change the logging section in this file. The logging section has a structure with channels and categories.

sudo cp /etc/named/named.conf /etc/named/named.conf.backup

Setting Up Logging Channels

Logging channels say where log messages go and how they look. You can make multiple channels for different log types. Here's an example of a channel:

channel example_channel {
    file "/var/log/named/example.log" versions 3 size 5m;
    severity dynamic;
    print-time yes;
};

This channel writes logs to a file, keeps three versions, limits file size to 5MB, uses dynamic severity, and adds timestamps.

Defining Log Categories

Log categories group related log messages. Named/Bind uses various categories for different event types. Some common categories are:

• default: Catches all messages not sent to other channels
• general: Messages about server operation
• database: Messages about zone loading and maintenance
• security: Messages about access control and authentication
• queries: Records incoming queries (if enabled)
• client: Client-related messages

To assign a category to a channel, use this syntax:

category example_category { example_channel; };

By setting up multiple channels and categories, you can create a logging system that captures all needed information about your DNS server's operation.

logging {
    channel default_file {
        file "/var/log/named/default.log" versions 3 size 5m;
        severity dynamic;
        print-time yes;
    };
    channel security_file {
        file "/var/log/named/security.log" versions 3 size 5m;
        severity info;
        print-time yes;
    };
    channel query_file {
        file "/var/log/named/query.log" versions 3 size 5m;
        severity info;
        print-time yes;
    };

    category default { default_file; };
    category security { security_file; };
    category queries { query_file; };
};

Creating Separate Log Files

Using separate log files for different categories has benefits:

1. Easier troubleshooting: Find specific information quickly without searching through a large, combined log file.
2. Better organization: Each log file contains related events, making it easier to analyze patterns.
3. Improved performance: Writing to multiple files can be faster than writing to a single file, especially on systems with high query volumes.

Example file paths and naming conventions:

/var/log/named/default.log
/var/log/named/security.log
/var/log/named/query.log
/var/log/named/zone-transfer.log
/var/log/named/update.log

Use clear names that show the content of each log file.

Configuring Log Rotation

Log rotation is important because it:

1. Prevents log files from growing too large and using too much disk space.
2. Makes it easier to archive and manage older log data.
3. Helps maintain system performance by keeping log files at a manageable size.

To set up log rotation in the logging configuration:

1. Use the "versions" parameter to specify the number of old log files to keep.
2. Use the "size" parameter to set the maximum size of each log file before rotation occurs.

Example:

channel example_channel {
    file "/var/log/named/example.log" versions 5 size 10m;
    severity dynamic;
    print-time yes;
};

This configuration keeps 5 versions of the log file and rotates when the file reaches 10 MB.

Setting Appropriate Severity Levels

Named/Bind offers several severity levels for logging:

1. critical
2. error
3. warning
4. notice
5. info
6. debug (with levels 1-3)

Guidance for choosing severity levels:

• Use "critical" and "error" for serious issues that need immediate attention.
• Use "warning" for potential problems that don't immediately affect operations.
• Use "notice" or "info" for routine operational information.
• Use "debug" levels for detailed troubleshooting, but be careful as they can generate large volumes of logs.

Example:

channel security_channel {
    file "/var/log/named/security.log" versions 3 size 5m;
    severity warning;
    print-time yes;
};

channel query_channel {
    file "/var/log/named/query.log" versions 3 size 5m;
    severity info;
    print-time yes;
};

In this example, security-related logs use the "warning" severity to capture important security events, while query logs use "info" to record routine query information.

channel debug_channel {
    file "/var/log/named/debug.log" versions 2 size 20m;
    severity debug 3;
    print-time yes;
};

category default { debug_channel; };

Restarting the Named Service

After changing your logging configuration, restart the Named service to apply the changes. The restart command depends on your operating system:

For systemd-based systems (like modern Ubuntu or CentOS):

sudo systemctl restart named

For older init.d-based systems:

sudo service named restart

For FreeBSD:

sudo service named restart

After restarting, check the system logs to confirm that the Named service started without errors.

sudo systemctl status named

sudo service named status

Checking Log Files

To verify that logs are generated correctly:

1. Wait a few minutes after restarting the service to allow log entries to accumulate.
2. Check the log files you set up in the named.conf file.
3. Use the 'tail' command to view the most recent log entries:

   sudo tail -f /var/log/named/example.log

4. Look for timestamps that match the current time, indicating new log entries.

Tips for reading log entries:

• Note the severity level of each entry.
• Look for patterns in the types of events logged.
• Check that the expected categories (queries, security, etc.) are in the logs.

Common Logging Issues and Solutions

1. No logs generated:

   • Check file permissions on the log directory and files.
   • Verify that the paths in named.conf are correct.
   • Make sure the Named service is running.

2. Wrong severity levels:

   • Review the severity settings in named.conf.
   • Adjust severity levels to capture the needed information.

3. Missing log categories:

   • Check that all needed categories are defined in named.conf.
   • Make sure each category is linked to a valid channel.

4. Log files growing too fast:

   • Review and adjust the size and versions settings in the channel configurations.
   • Consider increasing log rotation frequency.

5. Errors in named.conf:

   • Use the named-checkconf tool to validate your configuration:

     named-checkconf /etc/named.conf

   • Fix any syntax errors reported by the tool.

6. Performance issues due to too much logging:

   • Consider reducing the logging level for high-volume categories like queries.
   • Use separate physical disks for log files if possible to reduce I/O contention.

By following these steps and fixing common issues, you can make sure that your Named service is logging correctly and providing the information you need for monitoring and troubleshooting.

Balancing Logging Detail and System Resources

Detailed logging can affect system performance. More logs need more CPU and disk I/O, which can slow DNS responses. Consider these points:

1. CPU usage: Debug level logging can increase CPU usage.
2. Disk space: Detailed logs can fill up your disk quickly.
3. I/O operations: Frequent log writes can slow other disk operations.

To balance logging and performance:

1. Start with minimal logging and increase as needed.
2. Monitor system resources when changing log levels.
3. Use log rotation to manage file sizes.
4. Log to a separate disk to reduce I/O contention.
5. Adjust severity levels based on your needs.

Using Query Logging Selectively

Query logging records all DNS queries received by the server. This has benefits and drawbacks.

Benefits of query logging:

1. Identifies patterns in DNS usage.
2. Helps troubleshoot specific issues.
3. Can detect potential security threats.

Drawbacks of query logging:

1. Generates large amounts of data quickly.
2. Can impact performance on busy servers.
3. May raise privacy concerns.

When to use query logging:

1. During troubleshooting for specific issues.
2. On less busy servers where performance impact is small.
3. When investigating potential security incidents.
4. For short periods to analyze traffic patterns.

When enabling query logging, consider:

1. Logging to a separate file with rotation policies.
2. Using sampling to log only some queries.
3. Enabling it only on specific name servers.
4. Reviewing the need for query logging and disabling when not needed.

By managing your logging setup, you can gather needed information while minimizing the impact on your DNS server's performance.