What is DNS (Domain Name System)?

The Domain Name System (DNS) is the distributed directory that turns human-friendly names such as www.example.com into the IP addresses computers use to connect. Every visit to your site — by a person, Googlebot or an AI crawler — starts with a DNS lookup. If that lookup fails or is slow, nothing else about your SEO matters for that request. The system is defined in RFC 1034 and RFC 1035.

The records you’ll meet

$ dig +noall +answer example.com A
example.com.      300   IN   A      203.0.113.10

$ dig +noall +answer www.example.com CNAME
www.example.com.  3600  IN   CNAME  example.cdn-provider.net.

$ dig +noall +answer example.com TXT
example.com.      3600  IN   TXT    "google-site-verification=Xy7…q2c"
example.com.      3600  IN   TXT    "v=spf1 include:_spf.mailhost.example ~all"

The number after the name is the TTL in seconds — how long resolvers may cache the answer.

Why DNS matters for SEO

• Crawl failures. When Googlebot can’t resolve your domain, it can’t fetch anything. Google’s documentation on network and DNS errors explains that persistent DNS errors reduce crawling and, if they continue, can cause URLs to be dropped from the index. Search Console’s Crawl Stats report shows DNS resolution problems.
• Speed. DNS lookup time is part of every first visit’s latency and of TTFB (Time to First Byte) as measured from the browser.
• Migrations. Moving hosts or adding a CDN is mostly a DNS change. Plan it well and users and crawlers never notice.
• Certificates. CAA records and DNS-based validation affect whether your SSL certificate renews — and with it, HTTPS.

Changing DNS safely

1. A day or two before the change, lower the TTL of the records you’ll edit (for example from 86400 to 300 seconds).
2. Make the change once the old, longer TTL has expired everywhere.
3. Keep the old server running until traffic has fully moved — some resolvers cache longer than they should.
4. Raise the TTL again once everything is stable.

“Propagation” is simply caches expiring; lowering TTLs in advance is how you make it fast.

Common mistakes

• A CNAME at the bare domain (zone apex). The DNS rules don’t allow a CNAME alongside the SOA and NS records there; use your provider’s ALIAS/ANAME or CNAME-flattening feature instead.
• Forgetting the www record, or pointing it somewhere different from the apex.
• Deleting the Search Console verification TXT record during a cleanup and losing access.
• A CAA record that excludes the authority your host uses, breaking certificate renewal.
• Letting the domain registration lapse, which takes DNS down with it. Check the expiry date as well as the domain age.

How to check

The DNS Lookup shows A, AAAA, CNAME, MX, NS, TXT, SOA and CAA records for any domain, and parses SPF and DMARC with checks for common mistakes. Check before and after every migration.

Frequently asked questions