The DNS Library
Technical reference for DNS concepts, infrastructure, security, and filtering.
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Stub Resolvers: The DNS You Actually Use
An explanation of stub resolvers, the DNS components that run on endpoints and decide how name resolution behaves before any query leaves the device.
Why DNS Behavior Differs by Operating System
An explanation of how and why DNS resolution behavior varies across macOS, Windows, Linux, and mobile operating systems.
mDNS, LLMNR, and Local Name Resolution
Why local name resolution protocols exist, how they work, and how they interact with conventional DNS.
DNS Search Domains and Suffix Expansion
How operating systems modify and expand names before sending DNS queries, and why this behavior often surprises engineers.
VPNs, Split DNS, and Surprising Resolution Paths
How DNS behaves unexpectedly when traffic is split across multiple networks or trust boundaries, and why VPNs change where DNS questions are sent.
How DNS Filtering Works
A conceptual explanation of how DNS filtering fits into the DNS resolution process, and what is actually happening when a domain is blocked.
DNS 101: Introduction to the Domain Name System
An introduction to DNS explaining what problem it solves, why it is designed as a distributed system, and how its core roles fit together.
How DNS Resolution Works (At a High Level)
A conceptual walk through how a domain name becomes an answer, focusing on the resolution flow rather than individual record types.
Domain Names, Labels, and the DNS Namespace
An explanation of how domain names are structured, how labels function, and how the hierarchical DNS namespace enables delegation and resolution.
DNS Zones and Delegation
How the DNS namespace is divided into zones, how authority is delegated, and why zone boundaries shape control, caching, and failure behavior.
DNS Caching and TTL: How DNS Remembers (and Forgets)
An explanation of how DNS caching works, what TTL really controls, and why DNS changes propagate unevenly across the internet.
Recursive vs Authoritative DNS: Who Answers What, and Why
An explanation of the two major DNS server roles, how they interact during resolution, and why the separation matters operationally.
Anycast and DNS: Why the Same IP Exists Everywhere
An explanation of how IP anycast works, why it is heavily used in DNS infrastructure, and what it means operationally when the same address appears to exist in many places at once.
DNS at Scale: Latency, Load, and Failure Domains
How DNS behavior changes when systems grow large, and why latency, load, and failure domains dominate real-world design.
Common DNS Failure Modes and What They Look Like
An explanation of common DNS failure modes including SERVFAIL, timeouts, stale data, and partial outages, with guidance on what they mean and where they originate.
Change Management in DNS
Why DNS changes that seem simple often propagate slowly, inconsistently, or unexpectedly in real systems.
Why Attackers Use DNS
An architectural explanation of why DNS is frequently abused, rooted in how the protocol is designed and operated.
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How DNS Filtering Works
A conceptual explanation of how DNS filtering fits into the DNS resolution process, and what is actually happening when a domain is blocked.
Why Attackers Use DNS
An architectural explanation of why DNS is frequently abused, rooted in how the protocol is designed and operated.
mDNS, LLMNR, and Local Name Resolution
Why local name resolution protocols exist, how they work, and how they interact with conventional DNS.
DNS Search Domains and Suffix Expansion
How operating systems modify and expand names before sending DNS queries, and why this behavior often surprises engineers.