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My primary BIND server does not answer authoritatively, the secondary works as expected. What is wrong?

2 min read 27-10-2024
the ifix
My primary BIND server does not answer authoritatively, the secondary works as expected. What is wrong?

When managing a DNS (Domain Name System) infrastructure, it’s vital for both primary and secondary BIND (Berkeley Internet Name Domain) servers to function correctly. If you encounter an issue where your primary BIND server does not respond authoritatively while the secondary server works as expected, it’s essential to diagnose and resolve the underlying problems.

Problem Scenario

Original Code/Setup:

# Assume the zone file configuration in named.conf is correct.
zone "example.com" {
    type master;
    file "/etc/bind/db.example.com";
    allow-transfer { secondary_ip; };
};

Issue: The primary BIND server does not answer authoritatively.

Understanding the Issue

The primary BIND server should be authoritative for the zones it manages, meaning it responds to queries about these zones with the definitive answer. If it does not respond authoritatively, it could lead to various DNS resolution issues.

Possible Causes

  1. Configuration Errors:

    • Ensure that the named.conf file is correctly set up. The zone type should be defined as master for the primary server.
    • Check the zone file syntax for errors. A misconfigured DNS record may cause BIND to fail silently.

  2. DNS Record Issues:

    • Ensure the DNS records in the zone file are correctly defined. The absence of NS (Name Server) or SOA (Start of Authority) records could lead to the server appearing non-authoritative.

  3. BIND Service Status:

    • Verify if the BIND service is running without errors. Use systemctl status bind9 (on Linux) to check the service status.

  4. Firewall or Network Issues:

    • Firewall settings may block DNS queries to your primary server. Check if the DNS port (UDP 53) is open.

  5. Permissions on Zone Files:

    • The BIND process needs appropriate permissions to read zone files. Ensure that the user running BIND has read permissions on the zone file.

Diagnostic Steps

To troubleshoot, follow these diagnostic steps:

  1. Check BIND Logs: Look into the BIND logs located in /var/log/syslog or /var/log/named/named.log to identify any errors or warnings when starting the service or when processing queries.

  2. Use Dig Command: Utilize the dig command to test authoritative responses:

    dig @your_primary_server_ip example.com NS

    If this command returns answers indicating your primary server is non-authoritative, then you may need to examine the configuration further.

  3. Verify Zone File: Confirm that your zone file includes valid entries and is correctly formatted. Example:

    $TTL 86400
@   IN  SOA ns1.example.com. admin.example.com. (
        2023101001 ; Serial
        3600       ; Refresh
        1800       ; Retry
        604800     ; Expire
        86400 )    ; Negative Cache TTL
;
@   IN  NS  ns1.example.com.
ns1 IN  A   192.0.2.1

Conclusion

By methodically analyzing the configuration and connectivity of your primary BIND server, you can pinpoint the issues causing it to not answer authoritatively. Often, this issue can be resolved by correcting configuration errors, ensuring the service is running correctly, and validating the DNS records.

Additional Resources

By following the guidance in this article, you can effectively troubleshoot your BIND server and ensure that it operates as intended, providing authoritative DNS responses for your domains.

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