What is DNS lookup used for?
DNS Lookup lets you verify what the Internet actually sees for your domain. Unlike a simple local nslookup that uses your configured resolver, this tool queries multiple viewpoints simultaneously.
Main use cases:
- Outage diagnosis -> Is your site down? Check if A/AAAA points to the correct IP
- Post-change verification -> After modification, confirm resolvers have the new value
- Email authentication audit -> Verify SPF, DKIM, DMARC are correctly published
- Migration preparation -> Compare before/after responses to validate the transition
How to use DNS Lookup in 3 steps
Step 1: Enter the domain
Type the domain name to check in the search field. You can enter:
- An apex domain:
captaindns.com - A subdomain:
www.captaindns.com - A specific record:
_dmarc.captaindns.com
Step 2: Choose type and resolver
Record types:
- A: IPv4 address
- AAAA: IPv6 address
- CNAME: Alias to another name
- MX: Mail servers
- TXT: Free text (SPF, DKIM, verifications)
- NS: Name servers
Available resolvers:
- Google DNS (8.8.8.8)
- Cloudflare (1.1.1.1)
- Quad9 (9.9.9.9)
- OpenDNS
- Authoritative server
Step 3: Analyze results
The response displays:
- Data: The record value
- TTL: Time remaining in cache
- Latency: Resolver response time
- RCODE: Status (NOERROR, NXDOMAIN, SERVFAIL)
Understanding TTL and propagation
TTL (Time To Live) is often misunderstood. It's not magical "propagation" - it's simply a cache duration.
| TTL | Meaning | Use case |
|---|---|---|
| 300 (5 min) | Changes visible quickly | Migrations, testing |
| 3600 (1h) | Performance/freshness balance | Common usage |
| 86400 (24h) | Maximum performance | Stable records |
Migration tip:
- 48h before: Lower TTL to 300
- D-Day: Make the change
- After stabilization: Raise TTL to 3600 or more
Iterative trace: understanding resolution
Iterative trace shows each step of DNS resolution, from root to authoritative server.
Example trace for captaindns.com A:
1. Root (.) -> Returns .com servers
Latency: 15ms
2. TLD (.com) -> Returns captaindns.com NS
Latency: 25ms
3. Authoritative (ns1.provider.com) -> Responds A = 203.0.113.50
Latency: 45ms
TTL: 3600
When to use the trace?
- Slow resolution -> Identify which step is slowing down
- Intermittent SERVFAIL -> Find the problematic server
- Difference between resolvers -> Understand where the gap comes from
- Support escalation -> Provide concrete evidence
DNS record types explained
Address records
| Type | Description | Example |
|---|---|---|
| A | IPv4 address | 203.0.113.50 |
| AAAA | IPv6 address | 2001:db8::1 |
Alias and delegation records
| Type | Description | Example |
|---|---|---|
| CNAME | Alias to another name | www -> captaindns.com |
| NS | Name servers | ns1.provider.com |
Email records
| Type | Description | Example |
|---|---|---|
| MX | Mail servers with priority | 10 mail.captaindns.com |
| TXT (SPF) | Sender authentication | v=spf1 include:_spf.google.com -all |
Security records
| Type | Description | Usage |
|---|---|---|
| CAA | Authorized certificate authorities | Controls who can issue certificates |
| DNSKEY | DNSSEC public key | Signature validation |
| DS | Delegation signer | DNSSEC trust chain |
FAQ - Frequently asked questions
Q: How does a DNS lookup work?
A: Your query is sent to the selected resolver (Google, Cloudflare, etc.). The resolver checks its cache or queries the DNS chain (root -> TLD -> authoritative) to get the response.
Q: What's the difference between resolvers?
A: Each resolver has its own cache and may have different responses at any given moment depending on when it cached the value. The authoritative server always provides the freshest response.
Q: What does the displayed TTL mean?
A: TTL (Time To Live) indicates how many seconds the response remains in the resolver's cache before it queries the authoritative server again. Lower TTL = changes visible faster.
Q: When should I use iterative trace?
A: Use the trace to diagnose slow resolution, understand differences between resolvers, or identify delegation or authoritative server issues.
Q: Why do responses differ between resolvers?
A: It's the DNS caching mechanism. If a resolver queried your zone before your modification, it keeps the old response until TTL expiration.
Complementary tools
| Tool | Purpose |
|---|---|
| Propagation Test | Compare responses from dozens of resolvers simultaneously |
| DNS Audit | Check your domain's complete health |
| SPF Inspector | Analyze your SPF record in detail |
| Email Tester | Test SPF/DKIM/DMARC from your server |
Useful resources
- RFC 1035 - Domain Names Implementation (DNS specification)
- Google Public DNS Documentation (usage guide)
- Cloudflare 1.1.1.1 Documentation (Cloudflare resolver)
- IANA - DNS Parameters (official record type registry)