DNSSEC Validation Failed: Diagnosis and Repair

Troubleshooting Guide • Updated December 2024

DNSSEC validation failure means a validating resolver rejected your DNS response as untrustworthy. This causes SERVFAIL responses and makes your domain unreachable for users on validating resolvers.

Site Down? If your site is currently unreachable, skip to the Emergency Fix section.

Common Causes of Validation Failure

1. Expired Signatures

RRSIG records have expiration timestamps. If your zone isn't re-signed before expiration, validation fails.

Symptoms: Site worked previously, now fails on validating resolvers.

Fix: Re-sign your zone. Most managed DNS providers (Cloudflare, Route 53) handle this automatically. If self-hosted, check your signing daemon.

2. DS Record Mismatch

The DS record at the parent zone doesn't match your DNSKEY. This breaks the chain of trust.

Symptoms: Validation failed immediately after enabling DNSSEC or changing providers.

Fix: Verify the DS record values at your registrar match what your DNS provider requires. Even one wrong character causes failure.

3. Missing DS Record

Zone is signed but no DS record exists at the parent. Resolvers can't establish trust.

Symptoms: DNSSEC shows enabled at DNS provider, but verification tools show "insecure" or validation fails.

Fix: Add the DS record at your domain registrar. This is separate from your DNS provider.

4. Algorithm Mismatch

DS record specifies a different algorithm than the actual DNSKEY uses.

Fix: Regenerate the DS record from current keys, or reconfigure keys to match registered algorithm.

Diagnostic Steps

Check with dig

dig +dnssec +cd yourdomain.com @8.8.8.8

The +cd flag disables validation—if this returns results but without +cd fails, you have a validation problem.

Use Online Analyzers

Check Signature Expiration

dig +dnssec yourdomain.com RRSIG

Look for the expiration timestamp in RRSIG records. If past, signatures have expired.

Emergency Fix: Disable DNSSEC

If your site is down and you need it restored immediately:

Remove DS Record First

Log in to your registrar and delete the DS record. This is critical—removing DNSSEC at the DNS provider first causes extended outage.

Wait for Propagation

DS record removal can take 1-48 hours depending on TTL. Check with dig DS yourdomain.com until empty.

Disable at DNS Provider

After DS is removed from parent zone, disable DNSSEC at your DNS provider.

Important Order: Always remove DS at registrar BEFORE disabling DNSSEC at DNS provider. Reversing this order causes outage until DS TTL expires.

Prevention

  • Use managed DNSSEC: Cloudflare, Route 53, and similar providers handle signatures automatically
  • Monitor expiration: Set alerts for signature expiration if self-managed
  • Test before changes: Use staging domain to test DNSSEC changes
  • Document DS records: Keep records of current DS values for quick comparison

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