DNS Lookups
"It's always DNS."
Half the networking problems you'll debug come down to DNS. Let's master the tools.
dig - The Gold Standard
Terminal
$dig google.com
;; QUESTION SECTION:
;google.com. IN A
;; ANSWER SECTION:
google.com. 299 IN A 142.250.185.78
Short Answer
Terminal
$dig +short google.com
142.250.185.78
+short gives just the IP - perfect for scripts.
Query Specific Record Types
Terminal
$dig MX google.com +short
10 smtp.google.com.
20 smtp2.google.com.
$dig NS google.com +short
ns1.google.com.
ns2.google.com.
$dig TXT google.com +short
"v=spf1 include:_spf.google.com ~all"
Common record types:
| Type | Contains |
|---|---|
| A | IPv4 address |
| AAAA | IPv6 address |
| MX | Mail servers |
| NS | Name servers |
| TXT | Text records (SPF, DKIM, etc.) |
| CNAME | Alias to another domain |
Query Specific DNS Server
Terminal
$dig @8.8.8.8 google.com +short
142.250.185.78
@8.8.8.8 uses Google's DNS instead of system default. Useful for testing.
nslookup - Quick and Simple
Terminal
$nslookup google.com
Server: 127.0.0.53
Address: 127.0.0.53#53
Non-authoritative answer:
Name: google.com
Address: 142.250.185.78
Use Specific Server
Terminal
$nslookup google.com 8.8.8.8
(uses Google's DNS)
host - Simplest Option
Terminal
$host google.com
google.com has address 142.250.185.78
google.com has IPv6 address 2607:f8b0:4004:800::200e
google.com mail is handled by 10 smtp.google.com.
Terminal
$host 142.250.185.78
78.185.250.142.in-addr.arpa domain name pointer lga25s71-in-f14.1e100.net.
host IP does reverse DNS (IP to name).
Checking DNS Configuration
Terminal
$cat /etc/resolv.conf
nameserver 127.0.0.53
nameserver 8.8.8.8
This shows which DNS servers your system uses.
Troubleshooting DNS
Site Won't Load - Is It DNS?
Terminal
$dig example.com +short
(empty - no response)
$dig @8.8.8.8 example.com +short
93.184.216.34
Local DNS failed, Google's works → local DNS problem.
Wrong IP Being Returned
Terminal
$dig mysite.com +short
1.2.3.4
$# Expected 5.6.7.8 - DNS cache is stale
DNS Propagation
After changing DNS records, it can take hours to propagate. Test with different DNS servers to check propagation:
hljs bash
dig @8.8.8.8 site.com # Google
dig @1.1.1.1 site.com # Cloudflare
dig @9.9.9.9 site.com # Quad9
Knowledge Check
How do you check if a DNS issue is with your local DNS server specifically?
Quick Reference
| Command | Purpose |
|---|---|
dig domain | Full DNS query |
dig +short domain | Just the IP |
dig @8.8.8.8 domain | Use specific DNS server |
dig MX domain | Mail server records |
nslookup domain | Simple lookup |
host domain | Simplest lookup |
host IP | Reverse lookup |
Key Takeaways
digis the most powerful DNS tooldig +shortfor quick IP lookups- Test different DNS servers to isolate problems
- Check
/etc/resolv.conffor DNS configuration - "It's always DNS" - check DNS first when debugging
Next: making HTTP requests with curl.