DNS Resolution Workbench

DNS Resolution Workbench

Step through recursive client queries, iterative resolver lookups, referrals, authoritative answers, cache hits, CNAME chains, and NXDOMAIN behavior

Interactive DNS resolution animation for learning recursive resolvers, iterative queries, root and TLD referrals, authoritative answers, TTL caching, CNAME chains, and negative caching.

Animation DNS Recursive Resolver Caching

DNS Resolution Workbench

Follow a hostname lookup from an IoT device to a recursive resolver, then through root, TLD, and authoritative DNS servers. Each step highlights who is asking, who is answering, what gets cached, and why a later lookup can be much faster.

Step 0/0Resolution progress

ReadyCurrent message

Cache emptyResolver cache state

No answer yetClient result

TrySelect NXDOMAIN, request AAAA for missing.iotclass.org, and Step from the Recursive Resolver through root, TLD, and authority.

ObserveLookup outcome becomes NXDOMAIN, Resolver cache state stores the negative answer for TTL 120 s, and a repeat lookup avoids upstream messages.

ExplainThe resolver follows referrals until 1 authoritative zone answers; its SOA-derived negative TTL permits caching non-existence just as a positive TTL bounds address reuse.

Technical boundariesThe trace omits DNSSEC validation, glue/bailiwick rules, EDNS truncation, TCP/DoT/DoH transport, retries, lame delegations, anycast selection, cache eviction, and concurrent queries.

Colour keyfundamentals identitycurrent / primaryreference / datasuccesscautionerror / failure

Scenarios

Controls

Record type A A - IPv4 address AAAA - IPv6 address

What To Watch

A client normally asks one recursive resolver. The resolver performs iterative work upstream and returns the final answer or error.

Recursive requestClient asks the resolver to finish the lookup.

ReferralRoot and TLD servers point the resolver closer to authority.

AuthoritativeThe zone server returns the final record or NXDOMAIN.

TTL cacheCached records avoid upstream queries until TTL expires.

Resolution Path

Choose Step or Play

No query sent yetCurrent packet

Start with a client requestWhy this step matters

Resolver has not answeredLookup outcome

Resolver Cache

Name	Type	Cached value	TTL	Status

Learning Diagnosis

Mode pendingStep through the lookup to see where recursive behavior stops and iterative behavior begins.

Cache not used yetThe resolver cache is empty until a response with a TTL is stored.

Troubleshooting signalA DNS failure can be a local resolver issue, an upstream referral problem, an authoritative error, or simply a cached negative answer.

Resolver Transcript

Quick Reference

DNS Actors

• Stub resolver: client-side code in the OS or app.
• Recursive resolver: performs lookup work for the client.
• Authoritative server: holds the zone data for a name.

Resolution Flow

• Client asks resolver recursively.
• Resolver asks root, TLD, then authoritative servers iteratively.
• Resolver returns an answer, CNAME chain, or DNS error.

TTL And Cache

• Positive answers are cached for their TTL.
• Negative answers can be cached using SOA-derived timing.
• Short TTLs speed changes but increase query load.

How To Read The Animation

Orange messageA query or referral-seeking request is moving away from the resolver.

Green messageAn answer, referral, CNAME, cache response, or error is moving back toward the resolver or client.

Cache tableRows appear when the resolver can reuse information. A cache-hit scenario starts with valid cached data.

Technical Accuracy Notes

Recursive vs IterativeThe client-to-recursive-resolver request is modeled as recursive. Root, TLD, and authoritative interactions are modeled as iterative resolver queries and referrals.

What Is SimplifiedUDP/TCP fallback, EDNS, DNSSEC validation, glue details, resolver selection, search suffixes, and transport encryption are intentionally omitted from the main animation.

IoT RelevanceDevices often rely on DHCP-provided resolvers, cloud endpoint names, MQTT broker names, and cached DNS behavior during intermittent connectivity.

Source Links

RFC 1034 - Domain ConceptsDefines DNS hierarchy, zones, resolvers, recursive service, and caching concepts.

RFC 1035 - DNS ImplementationDefines DNS message and resource record details used by classic DNS lookups.

RFC 2308 - Negative CachingExplains caching of negative DNS answers such as NXDOMAIN.