DNS Troubleshooting Cheat Sheet: 10 Checks Every Sysadmin Should Know

DNS Troubleshooting Cheat Sheet: 10 Checks Every Sysadmin Should Know Tags: dns, networking, devops, webdev Every sysadmin has been there — a website goes down, email stops delivering, or SSL certificates expire at 2 AM. Having a systematic troubleshooting workflow saves hours of guesswork. Here are 10 essential DNS and network checks I run on every issue, with the commands and free online tools to do them instantly. 1. DNS Propagation Check When you update DNS records, changes don't happen instantly. DNS propagation can take up to 48 hours depending on TTL values. What to check: Query multiple global DNS servers to see if your changes have propagated. dig @8.8.8.8 example.com A dig @1.1.1.1 example.com A dig @9.9.9.9 example.com A Or check 30+ servers at once with DNS Propagation Checker . 2. WHOIS / RDAP Lookup Domain expired? Ownership dispute? WHOIS tells you registration dates, registrar, and nameservers. whois example.com RDAP is the modern replacement — structured JSON, no rate