DNS (Domain Name System) is like the phone book of the internet. We type google.com, and DNS figures out the IP address (like 142.250.80.46) so our browser knows where to connect.
Without DNS, we’d have to memorize IP addresses for every website. Nobody wants that.
The Resolution Flow
When we type a URL in the browser, here’s what happens behind the scenes:
Most lookups never reach step 4 because caching is aggressive. The resolver already knows the answer from previous queries.
DNS Record Types
These are the building blocks of DNS configuration.
| Record | Purpose | Example |
|---|---|---|
| A | Maps domain to IPv4 address | pman47.cc → 144.24.126.230 |
| AAAA | Maps domain to IPv6 address | pman47.cc → 2001:db8::1 |
| CNAME | Alias pointing to another domain | www.pman47.cc → pman47.cc |
| MX | Mail server for the domain | pman47.cc → mail.pman47.cc (priority 10) |
| TXT | Arbitrary text (SPF, DKIM, verification) | v=spf1 include:_spf.google.com ~all |
| NS | Which nameservers are authoritative | pman47.cc → ns1.hostinger.com |
A CNAME can’t coexist with other records on the same name. So we can’t have a CNAME at the root domain (pman47.cc) — only on subdomains (www.pman47.cc). Some providers offer “ALIAS” or “ANAME” records to work around this.
TTL — Time to Live
Every DNS record has a TTL (in seconds) that tells caches how long to keep the answer.
TTL 300→ cache for 5 minutes (good for records we might change)TTL 86400→ cache for 24 hours (good for stable records)- Before a migration, lower the TTL to 60-300 so changes propagate fast
DNS Lookup Commands
dig and nslookup are our go-to tools for DNS debugging.
# dig — the gold standard
dig pman47.cc # query A record
dig pman47.cc AAAA # query IPv6 record
dig pman47.cc MX # query mail records
dig pman47.cc +short # just the IP, no extra info
dig @8.8.8.8 pman47.cc # query using Google's DNS
# nslookup — simpler alternative
nslookup pman47.cc
nslookup -type=MX pman47.cc# Trace the full resolution path
dig pman47.cc +trace
# Check all record types
dig pman47.cc ANY +shortCommon DNS Gotchas
- Propagation delay — DNS changes can take minutes to hours to spread worldwide because of caching. Lower the TTL before making changes.
- CNAME at root — Most providers don’t allow it. Use an A record for the naked domain.
- /etc/hosts — Local override file. The OS checks this before DNS. Useful for testing:
127.0.0.1 myapp.local. - DNS caching — If things look wrong after a change, flush the local cache:
sudo systemd-resolve --flush-caches(Linux) orsudo dscacheutil -flushcache(macOS).
In simple language, DNS is just a giant distributed phone book. We give it a name, it gives us back a number. The whole system is designed to be fast (caching) and reliable (multiple levels of servers).