What you will learn
- Trace a DNS lookup
- Know A, CNAME, MX, TXT records
- Debug resolution failures
New to this? Start here
The basics, in plain English
Humans remember names like google.com, but computers only talk in numbers (IP addresses). DNS is the system that looks up a name and returns its number, like a phonebook for the internet.
- Domain name
- A human-friendly name for a site, like example.com.
- DNS
- The “Domain Name System”: the service that turns a name into the IP address behind it.
- Resolve
- The act of looking up a name and getting back its address.
- A record
- A DNS entry that maps a name directly to an IP address.
- CNAME
- A DNS entry that points one name at another name (an alias).
- TTL
- “Time to live”: how long an answer can be cached before asking again. This is why DNS changes feel slow.
01
Resolution
A resolver walks from root to TLD to authoritative servers. Caching and TTLs make it fast but also cause stale-record headaches.
Try it yourself
bash
$dig example.com A↳Look up the A record (the IPv4 address) for the domain.$dig example.com MX +short↳Find the mail servers for the domain, output trimmed.$nslookup example.com↳Quick interactive DNS lookup.$dig +trace example.com↳Walk the full DNS chain from root servers down, step by step.↳ lines explain what each command does — only the commands get copied
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