DNS Time Long Troubleshooting Guide
Issue Description
DNS resolution time is consistently longer than expected.
Normal DNS Time
| Quality | DNS Time |
|---|---|
| Good | <50ms |
| Normal | 50-200ms |
| Poor | >200ms |
Systematic Analysis Approach
Step 1: Identify Pattern
- Which regions affected?
- Which ISPs affected?
- When did it start?
- Is it continuous or intermittent?
Step 2: Check DNS Path
1. Local DNS (LDNS) → Recursive DNS
2. Recursive DNS → Root DNS
3. Root DNS → TLD DNS
4. TLD DNS → Authoritative DNS
Step 3: Analyze Each Hop
- LDNS response time
- Recursive DNS time
- Authority chain length
- Each query response time
Step 4: Identify Bottleneck
- Slow LDNS
- Slow recursive DNS
- Long authority chain
- Network latency to DNS servers
Common Causes
DNS Server Issues
- LDNS server overload
- Recursive DNS slow
- Authoritative DNS slow
- DNS cache misses
Network Issues
- High latency to DNS servers
- Packet loss to DNS servers
- Routing issues
- DNS server distance
Configuration Issues
- Too many CNAME records
- Long DNS chain
- Missing DNS records
- DNS misconfiguration
Resolution Steps
Quick Fixes
- Use public DNS (8.8.8.8, 1.1.1.1)
- Increase DNS cache TTL
- Reduce CNAME chain
- Fix DNS configuration
Long-term Solutions
- Deploy local DNS resolvers
- Implement DNS caching
- Optimize DNS records
- Use DNS preload/prefetch
Monitoring
- Set up DNS time alerts
- Monitor DNS trends
- Track DNS provider performance
- Regular DNS audits
Tools
- nslookup: Test DNS resolution
- dig: Detailed DNS information
- DNSViz: DNS visualization
- DNSPerf: DNS performance comparison