DNS & Technical

DNS propagation is the process by which updated DNS records spread to resolvers and caching servers around the world. When you change a DNS record, each server must wait for its cached copy to expire (based on the TTL value) before fetching the new record. Full propagation typically takes a few hours but can take up to 48 hours in rare cases.

An A record maps a domain directly to an IPv4 address (e.g., 192.0.2.1), while a CNAME (Canonical Name) record points a domain to another domain name instead of an IP address. CNAMEs are useful for aliases — for example, pointing www.example.com to example.com. You cannot use a CNAME at the root (apex) of a domain alongside other records.

Nameservers are servers that store the DNS records for your domain and answer queries about it. When someone types your domain into a browser, their DNS resolver contacts your domain's nameservers to find the correct IP address. You set your nameservers at your registrar, typically pointing to your hosting provider or DNS management service.

TTL (Time to Live) is a value in seconds attached to each DNS record that tells resolvers how long to cache the record before fetching a fresh copy. A low TTL (e.g., 300 seconds) means changes propagate quickly but increases query load on your nameservers. A high TTL (e.g., 86400 seconds / 24 hours) reduces query load but slows propagation of updates.

DNSSEC (Domain Name System Security Extensions) adds cryptographic signatures to DNS records, allowing resolvers to verify that responses have not been tampered with — protecting against DNS spoofing and cache poisoning attacks. It is recommended for domains where security is critical, though it requires support from both your registrar and DNS provider, and misconfiguration can make your domain unreachable.

An MX (Mail Exchanger) record is a DNS record that specifies which mail servers are responsible for accepting email messages on behalf of a domain. Each MX record includes a priority value — lower numbers indicate higher priority — so multiple mail servers can be configured for redundancy. Without a correctly configured MX record, email sent to your domain will not be delivered.

A TXT (Text) record is a DNS record that stores human-readable or machine-readable text associated with a domain. TXT records have many uses: domain ownership verification (for Google Search Console, for example), email authentication via SPF and DKIM, DMARC policies, and other service configurations. A single domain can have multiple TXT records, though conflicts between SPF records must be avoided.

An AAAA record maps a domain name to an IPv6 address — the 128-bit successor to IPv4 that provides a vastly larger address space. IPv6 addresses look like '2001:0db8:85a3::8a2e:0370:7334'. Hosting providers increasingly support dual-stack configurations where both an A record (IPv4) and an AAAA record (IPv6) point to the same server, allowing clients to connect over either protocol.

A DNS zone file is a plain-text file stored on a nameserver that contains all DNS records for a domain — including A, AAAA, CNAME, MX, TXT, NS, and SOA records. It begins with a Start of Authority (SOA) record that describes the zone's primary nameserver and administrative contact. Most hosting control panels and DNS providers abstract zone file editing behind a graphical interface, but understanding the format is useful for advanced configurations and migrations.

A wildcard DNS record uses an asterisk (*) as the leftmost label and matches any subdomain that does not have a more specific record defined. For example, '*.example.com' would resolve for 'anything.example.com'. Wildcards are commonly used by platforms that generate per-user or per-tenant subdomains. They can also be used with wildcard SSL certificates to secure all subdomains under a single certificate.

The root DNS servers are 13 logical server clusters (labeled A through M) at the top of the DNS hierarchy. They hold the authoritative list of all TLD nameservers and are the starting point of every recursive DNS lookup when a resolver has no cached answer. The 13 addresses are operated by organizations including ICANN, Verisign, NASA, and university research networks, and are replicated via anycast across hundreds of physical locations worldwide for resilience and speed.

Anycast is a network routing technique where multiple servers share the same IP address and incoming traffic is automatically routed to the nearest or best-performing server. DNS providers like Cloudflare and Google use anycast to serve DNS queries from data centers close to the user, reducing latency. Anycast also provides DDoS resilience — attack traffic is distributed across many nodes rather than overwhelming a single server.

Reverse DNS (rDNS) maps an IP address back to a domain name using PTR (Pointer) records stored in the in-addr.arpa zone for IPv4 or ip6.arpa for IPv6. A forward lookup maps domain → IP; a reverse lookup maps IP → domain. PTR records are controlled by whoever owns the IP block (typically your hosting provider or ISP), not your registrar. Correctly configured reverse DNS is important for email deliverability — many mail servers reject messages from IPs without matching rDNS.

A CAA (Certification Authority Authorization) record specifies which certificate authorities (CAs) are permitted to issue SSL/TLS certificates for your domain. By publishing a CAA record, you can restrict certificate issuance to one or more trusted CAs, reducing the risk of a rogue CA issuing an unauthorized certificate for your domain. CAA records are checked by CAs before issuance but do not prevent already-issued certificates from remaining valid.

DNS over HTTPS (DoH) is a protocol that encrypts DNS queries inside standard HTTPS traffic, preventing ISPs, network administrators, or attackers on the same network from seeing which domains you look up. DoH is supported by major browsers including Chrome and Firefox, as well as public resolvers like Cloudflare (1.1.1.1) and Google (8.8.8.8). While DoH improves privacy, it can bypass local network DNS filtering, which is a consideration for enterprise environments.

DNS over TLS (DoT) encrypts DNS queries using the TLS protocol on a dedicated port (853), keeping DNS traffic private from eavesdroppers. Unlike DNS over HTTPS (DoH), DoT uses a separate port that network operators can identify and manage, making it more suitable for enterprise environments where DNS traffic needs to be audited. Both DoT and DoH offer similar privacy benefits; the main difference is how they blend in with other traffic.

DNS load balancing distributes traffic across multiple servers by returning different IP addresses in response to the same domain query. In its simplest form — round-robin DNS — multiple A records are added for the same hostname, and resolvers cycle through them. More sophisticated approaches use weighted records, geographic routing (returning the nearest server's IP based on the client's location), and health-check-based failover to automatically remove IPs for unhealthy servers.

A glue record is an A record stored at the parent TLD zone that provides the IP address of a nameserver whose hostname is within the domain it serves — breaking what would otherwise be a circular dependency. For example, if ns1.example.com is a nameserver for example.com, the .com registry must hold the IP address of ns1.example.com (a glue record) so resolvers can find it. Glue records are required when you set up custom (vanity) nameservers using your own domain.

DNS delegation is the process by which a parent zone grants authority over a subdomain to another set of nameservers. For example, the root zone delegates .com to Verisign's nameservers, and Verisign's zone delegates example.com to whatever nameservers the registrant configures. This hierarchy of delegations forms the distributed, decentralized structure of the global DNS. Each delegation is recorded with NS records in the parent zone.

An NS (Name Server) record identifies the authoritative nameservers for a DNS zone. When a resolver is looking up a domain, it uses NS records to find which nameservers hold the authoritative answers. Every domain must have at least two NS records — a primary and a secondary — for redundancy. NS records are set both at your registrar (to tell the registry where your zone lives) and within your zone file itself.

DNS caching stores the results of DNS queries locally — in your operating system, your browser, or your ISP's recursive resolver — so that repeated lookups for the same domain do not require a full trip back to the authoritative nameserver. Each cached record is kept for the duration specified by its TTL (Time to Live). Caching dramatically speeds up browsing but means DNS changes do not take effect immediately for users who have recently visited a domain.

An authoritative DNS server holds the official DNS records for a domain and answers queries with definitive answers — it does not guess or ask elsewhere. A recursive DNS resolver (like your ISP's DNS or Cloudflare 1.1.1.1) accepts queries from clients and works through the DNS hierarchy — asking root servers, then TLD servers, then authoritative servers — to resolve a name. Resolvers cache results to improve speed; authoritative servers do not recurse.

An SRV (Service) record specifies the hostname and port number for specific services running on a domain. The record format includes the service name, protocol, priority, weight, port, and target hostname — for example, '_xmpp-client._tcp.example.com'. SRV records are widely used by VoIP (SIP), instant messaging (XMPP), and game servers to allow clients to discover service endpoints automatically without hardcoding ports.

Flushing your local DNS cache forces your device to fetch fresh DNS records instead of using stale cached results. On Windows, open Command Prompt and run 'ipconfig /flushdns'. On macOS, run 'sudo dscacheutil -flushcache && sudo killall -HUP mDNSResponder'. On Linux with systemd-resolved, run 'sudo systemd-resolve --flush-caches'. Browsers also maintain their own DNS cache; in Chrome, you can clear it via chrome://net-internals/#dns.

DNS failover is a technique that automatically changes DNS records to redirect traffic away from a failed server to a healthy backup. Monitoring agents continuously check server health; when a primary server goes down, the DNS provider updates the record (typically an A or CNAME) to point to a secondary server. Because DNS changes are subject to TTL-based caching, failover is fastest when TTL values are kept low (e.g., 60–300 seconds). Managed DNS providers like Cloudflare and AWS Route 53 offer built-in failover routing policies.