DNS Fundamentals
More to discover ↗A DNSSEC rollover replaces signing keys while keeping a valid chain of trust in place. Learn what to check before changing keys, how to stage a zone-signing key or key-signing key rollover, and when it is safe to remove old material.
Read article ↗DNSSEC helps a validating resolver detect forged DNS answers, but it does not encrypt queries, secure a website or make every DNS record trustworthy. Learn how its chain of trust works, where its limits are, and what to check when a signed domain stops resolving.
Read article · 4 min↗An SRV record tells compatible applications which host and port to use for a service. Learn how its fields work, how clients choose among multiple records, and what to check when a connection fails.
Read article · 4 min↗Glue records help DNS resolvers find a domain’s nameservers when those nameservers sit inside the domain they serve. Learn how the circular dependency arises, where glue is published, and what to check when a delegation is not working.
Read article · 3 min↗A DNS reply is easier to understand when you separate what was asked, what was answered, which servers are responsible, and what supporting records were included. Learn how to read the question, answer, authority, and additional sections without mistaking a referral for a final answer.
Read article · 4 min↗Learn how to use dig to request A, AAAA, MX, TXT, CNAME and other DNS record types, then read the response without mistaking an empty answer for a missing domain.
Read article · 4 min↗A PTR record lets a reverse DNS lookup find a name associated with an IP address. Learn how reverse lookup names work, who controls PTR records, and how to check a result without confusing it with ordinary forward DNS.
Read article · 4 min↗DNS lookups are often quick exchanges over UDP, but some answers and DNS operations need TCP. Learn how the two transports work, why a resolver may retry a query, and what a transport change means when troubleshooting.
Read article · 3 min↗The zone apex is the root of a DNS zone, while subdomains are names beneath it. Understanding the difference helps you place website, email, and verification records at the names where they will actually be used.
Read article · 4 min↗A wildcard DNS record can answer queries for names you have not created individually, but it is not a blanket rule for every subdomain. Learn how matching works, why existing names can block a wildcard, and what to check when a wildcard seems to be ignored.
Read article · 4 min↗A DNS TTL tells a cache how long it may reuse an answer about a record. Learn how the countdown works, why different users can see different answers after a change, and what TTL does—and does not—control.
Read article · 4 min↗TXT records can publish more than email settings. Learn how they help verify domain ownership, where to place them, why exact formatting matters, and how to check a record without disturbing existing DNS entries.
Read article · 4 min↗The Start of Authority record identifies a DNS zone and carries values used for zone transfers and negative caching. Learn what each field means, what it does not tell you, and how to read one safely.
Read article · 4 min↗NS records name the servers responsible for a DNS zone. Learn how they appear at delegation points and inside authoritative zones, how resolvers use them, and why glue records are sometimes needed.
Read article · 4 min↗A CNAME points one hostname to another hostname, while A and AAAA records point directly to IP addresses. Learn when an alias makes maintenance easier, when direct address records are better, and which DNS limitations to check before making the change.
Read article · 4 min↗A and AAAA records connect hostnames to different kinds of IP addresses. Learn how their formats differ, why a hostname might have both, and what to check when one connection path fails.
Read article · 4 min↗A DNS record is easier to understand when you read it one field at a time. Learn what the owner name, TTL, class, type, and value mean, and how to interpret common differences between zone files and lookup results.
Read article · 4 min↗A domain name is built from labels separated by dots, but its written form can depend on context. Learn how hostnames and fully qualified domain names relate, why a trailing dot matters in DNS tools and zone files, and how to read common names without confusing them with URLs.
Read article · 4 min↗A DNS zone is the portion of the domain name system managed as one administrative unit. Learn how zones relate to domains, what happens at a delegation boundary, and which records help a zone answer queries.
Read article · 4 min↗A stub resolver is the device-side part of a typical DNS lookup. Learn how it turns an app’s request into a DNS question, checks local answers, chooses a resolver and handles the reply.
Read article · 4 min↗A DNS lookup involves two different jobs: finding the right place to ask and providing the answer for a domain. Learn how recursive and authoritative servers work together, what caching changes, and which server to check when a record seems wrong.
Read article · 4 min↗DNS names form a hierarchy. Learn how the root, top-level domains, registered domains, subdomains and hostnames fit together, and how delegation helps a resolver find an answer.
Read article · 4 min↗When a site loads only sometimes, one of its IPv4 addresses may lead to a failing server. Learn how to list the addresses, test each one while preserving the correct hostname, and distinguish a server fault from DNS caching or another connectivity problem.
Read article · 4 min↗A domain can point to the right server and still show an HTTPS certificate warning. Learn how to separate DNS problems from certificate, hosting, and local-network issues without ignoring the warning.
Read article · 4 min↗A domain can resolve successfully while its website still returns an error. Learn what HTTP 404 and 500 responses tell you, how to check whether you reached the intended site, and what to investigate next.
Read article · 4 min↗A correct DNS answer does not guarantee that a server will serve the correct website. Learn how hostnames, HTTPS settings, proxies and redirects affect what visitors see, then follow a practical troubleshooting sequence.
Read article · 4 min↗When a website opens on mobile data but fails on home Wi-Fi, the difference is a useful troubleshooting clue—not proof that the website or your router is broken. Learn how to narrow the problem down to one device, your home network, DNS, or a particular connection path.
Read article · 4 min↗A VPN can change which DNS resolver your device uses, which networks it can reach, and whether a private domain name is available. Learn how to compare results safely and narrow down whether the problem is DNS, caching, or connectivity.
Read article · 4 min↗If a website works on one computer but not another, a local hosts file may be sending the domain to an unexpected IP address. Learn how to find the file, compare local resolution with DNS, and remove an outdated override safely.
Read article · 4 min↗A browser with secure DNS enabled may use a different resolver from the one your command-line tool queries. Learn how resolver choice, caches, VPNs, address types and browser behavior can produce different results—and how to compare them safely.
Read article · 4 min↗When a domain works for some visitors but not others, its authoritative nameservers may be serving different answers. Learn how to identify the delegated servers, query each one directly, compare the results, and decide what to check next.
Read article · 4 min↗A CNAME can point a website name through one or more aliases before DNS reaches an address. Learn how to follow that chain, recognize missing or circular links, and check the fix without confusing DNS failures with web redirects.
Read article · 4 min↗A website can appear healthy on IPv4 while its IPv6 address leads to timeouts or errors. Use this step-by-step approach to separate DNS problems from client-network, server, firewall, and application issues.
Read article · 4 min↗The bare domain and its www version are separate hostnames. Learn how to check DNS records, hosting settings, HTTPS certificates, and redirects to find out why one works while the other fails.
Read article · 4 min↗A registrar dashboard can show one set of nameservers while DNS answers appear to come from another. Learn how to check the parent delegation, compare it with authoritative nameserver responses, and narrow down the cause without making unnecessary changes.
Read article · 4 min↗When a website works on one network but not another, comparing DNS answers can help narrow down the cause. Learn how to query each resolver, interpret differences, and avoid mistaking normal caching or location-based answers for a fault.
Read article · 4 min↗A new hostname can be correctly configured yet continue to appear missing to some visitors. Learn how negative DNS caching works, what to check, and when waiting is the right next step.
Read article · 4 min↗A DNS update does not always move every visitor to a new server at once. Learn how to check authoritative records, cached answers, IPv6 addresses, redirects and hosting settings to find what is keeping a site on its old destination.
Read article · 4 min↗A DNS timeout does not always mean a domain is broken. Learn how to locate the failing step, compare resolvers, check authoritative nameservers, and distinguish network problems from other DNS errors.
Read article · 4 min↗A DNS SERVFAIL response means a resolver could not complete a query. Learn how to compare resolvers, check delegation and DNSSEC, and identify when the problem is local or domain-wide.
Read article · 4 min↗NXDOMAIN means a DNS resolver could not find the name it queried. If a domain or subdomain should exist, check the exact name, the authoritative DNS configuration, delegation, and cached negative answers before changing records.
Read article · 4 min↗A website can fail before your browser finds the server, while connecting to it, or during the HTTPS handshake. Learn how to identify where the failure occurs and choose a useful next check.
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