Troubleshooting DNS Propagation Issues

Fixing DNS Propagation Problems

After making DNS changes, you may find that some users can access your site while others cannot, or that changes seem to take longer than expected. This guide helps you diagnose and resolve common propagation issues.

Checking Propagation Status

Use these tools to check whether your DNS changes have propagated globally:

• whatsmydns.net – Shows DNS resolution from servers in multiple countries.
• dnschecker.org – Similar global propagation checker.
• Command line: Use nslookup yourdomain.com or dig yourdomain.com to check resolution from your local machine.

Common Causes of Slow Propagation

1. High TTL on Old Records

If the previous DNS record had a high TTL (e.g., 86400 seconds / 24 hours), resolvers worldwide may cache the old record for up to that duration. There is nothing you can do but wait for the cache to expire.

Prevention: Lower the TTL to 300 seconds at least 24 to 48 hours before making changes.

2. Local DNS Cache

Your computer and browser maintain their own DNS caches. Even if global propagation is complete, your local cache may still hold the old record.

Fix:

• Clear your browser cache and restart the browser.
• Flush your OS DNS cache:
  • Windows: ipconfig /flushdns
  • macOS: sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder
  • Linux: sudo systemd-resolve --flush-caches

3. ISP DNS Caching

Some ISPs cache DNS records aggressively and may not respect TTL values. Try switching to a public DNS resolver:

• Cloudflare: 1.1.1.1
• Google: 8.8.8.8

4. Incorrect Records

Double-check your DNS records for common mistakes:

• Typos in IP addresses or hostnames.
• Missing trailing dot on CNAME and MX targets.
• Conflicting records (e.g., a CNAME and A record for the same subdomain).

When to Contact Support

If propagation has not completed after 48 hours and you have verified your records are correct, contact SillyHost support for assistance.