Slow DNS resolution

Problem Summary

Slow DNS resolution delays the first connection to a domain before any file can be downloaded.

Performance Impact

• Delayed requests: DNS lookup happens before TCP and TLS connection setup
• Third-party cost: Many external domains multiply lookup time
• Worse first load: New visitors have fewer cached DNS results
• Regional variance: DNS performance can differ by location

How to Detect

1. Waterfall charts: Look for long DNS phases
2. WebPageTest: Test from multiple regions
3. DNS tools: Compare authoritative and recursive lookup times

Solutions

1. Use Reliable DNS Hosting

Move DNS to a fast, globally distributed provider when lookup time is consistently high.

2. Reduce External Domains

Each third-party domain adds connection setup work.

3. Add Preconnect Selectively

<link rel="preconnect" href="https://example.com">

4. Avoid Overusing DNS Prefetch

Hints help only for domains that are truly needed soon.