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Understand DNS and domains, one clear guide at a time
DNS is the system that turns a domain name into the address of a real server, routes your email, and proves who you are online. These guides explain each piece in plain language — accurate enough for engineers, clear enough for everyone else.
Buying a domain or trying to find out who owns one? The domain ownership and history guides cover WHOIS records, redaction and how to check a domain's past. Watching for lookalike, new or expiring domains, or keeping your own site online? The website monitoring guides cover uptime, SSL certificates and DNS hijacking.
Every guide pairs with a live who.is tool so you can look up real records as you read. Try a DNS lookup →
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Our daily roundup of the most interesting DNS changes across the web — hosting and CDN migrations, network moves, and security-config shifts.
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DNS Fundamentals
What is DNS?
A clear, complete guide to DNS: what the Domain Name System is, the name-to-IP hierarchy, how a query resolves step by step, caching, and zones.
9 min readWHOIS vs RDAP vs DNS
WHOIS and RDAP tell you who registered a domain and when it expires; DNS tells you where it points. Here is exactly what each one answers — and what it cannot.
9 min readIPv4 vs IPv6
IPv4 and IPv6 are the two versions of internet addresses. Learn how they differ, why IPv6 exists, how they coexist, and how each maps to DNS.
9 min readTTL & propagation
How DNS TTL controls caching, what "propagation" really means, and a safe playbook for changing records so updates take minutes, not days.
9 min readDomain Ownership & History
Checking a Domain's History
Six checks to run before you buy a used domain: past owners, drops and re-registrations, old versions of the site, blocklists, DNS and trademarks.
8 min readFinding a Domain's Past Owners
Current WHOIS rarely names the owner. Past WHOIS records, old copies of the site and a few other sources can show who owned a domain before.
7 min read"REDACTED FOR PRIVACY" Explained
Why WHOIS says REDACTED FOR PRIVACY, how that differs from a privacy service, which details stay public, and how to reach or identify the owner.
6 min readNew, Lookalike & Expiring Domains
Typosquatting & Lookalike Domains
How typosquatting and lookalike domains work, the patterns attackers use, how to find the ones copying your brand, and what to do when you find one.
8 min readNewly Registered Domains
What counts as a newly registered domain, what lists of them can show, why security teams treat them with caution, and how to follow the ones you care about.
7 min readExpiring & Dropping Domains
What happens to a domain after it expires, how long until it can be registered again, how to tell where a name is in that process, and the ways to catch it.
8 min readWebsite Monitoring
Uptime Monitoring & 99.9% Uptime
How much downtime 99%, 99.9% and 99.99% uptime allow, how uptime monitoring works, which settings matter, and how to tell if a site is down for everyone.
7 min readSSL Certificate Expiry
What visitors see when an SSL certificate expires, why automatic renewal still fails, how to check an expiry date, and how to get warned before it happens.
7 min readDNS Hijacking
The ways attackers take over a domain’s DNS, the records they change, how to spot a hijack early, and the locks that make one much harder.
8 min readDNS Record Types
DNS record types
A clear, practical guide to the DNS record types you actually use — A, AAAA, CNAME, MX, TXT, NS, SOA, PTR, SRV and CAA — with formats and examples.
11 min readA & AAAA records
A records map a name to an IPv4 address and AAAA records map it to IPv6. Learn their anatomy, how they work together, and how to check yours.
8 min readCNAME records
A CNAME record aliases one name to another canonical name. Learn how resolution follows the chain, the rules that trip people up, and how to check yours.
9 min readSOA records
What the SOA (Start of Authority) record is, its primary nameserver, admin email, serial number, and the refresh/retry/expire/minimum timers that drive DNS.
8 min readPTR & reverse DNS
What PTR records and reverse DNS (rDNS) are, how the in-addr.arpa and ip6.arpa zones work, who controls them, and why they matter for email.
9 min readSRV records
How SRV records advertise the host and port for a named service, what priority, weight, port, and target mean, and the rules that keep them valid.
9 min readEmail & Deliverability
MX records
How MX records route inbound email to the right mail servers, how priority works, and the gotchas (no CNAMEs, no IPs) that break delivery.
9 min readTXT, SPF, DKIM & DMARC
A precise guide to TXT records and the three pillars of email authentication — SPF, DKIM, and DMARC — how each works, where it lives, and how to roll it out.
11 min readDomains & Infrastructure
DNS Security
CAA records
How CAA records tell certificate authorities which CAs are allowed to issue TLS/SSL certificates for your domain — the format, a worked example, and the gotchas.
9 min readDNSSEC
How DNSSEC cryptographically signs DNS records so resolvers can verify answers are authentic and unmodified — what it protects, what it does not, and how to enable it.
11 min read