DNS Explained (Domain Name System)
DNS works like a phonebook for the internet. It translates human-readable domain names (e.g., amazon.com) into IP addresses (e.g., 205.251.242.103) that computers use to locate each other.
How DNS Resolution Works
1. User types "amazon.com" in browser
2. Computer asks DNS Resolver (usually from ISP/router)
3. Resolver checks cache, or asks Root -> TLD (.com) -> Authoritative server
4. Authoritative server returns IP address
5. Browser connects to that IP address
Common DNS Record Types
- A record: maps a domain to an IPv4 address
- AAAA record: maps a domain to an IPv6 address
- CNAME: alias pointing to another domain name
- MX record: specifies mail servers for a domain
Why IT Support Needs This
"This website won't load" issues are often DNS problems. Common fixes include flushing the DNS cache or checking DNS server settings.
Useful Commands
- Windows:
ipconfig /flushdns,nslookup amazon.com - macOS:
sudo dscacheutil -flushcache - Linux:
sudo systemd-resolve --flush-caches
Common Interview Talking Point
"If a user can't reach a specific website but others work fine, I'd check whether it's a DNS issue by trying nslookup on the domain, and testing if accessing the site by its raw IP address works."