DNS Resolution

CSC-263 · Semester IV · Computer Networks

beginner25 minAvailable

DNS Resolution Walkthrough

Follow an iterative resolution from root servers down to the authoritative nameserver

UDP/53

Hostname

Enter a hostname and press Resolve to walk the resolution chain.

Lab brief

Objective

Trace a host name from the root of the DNS hierarchy to its authoritative answer and interpret the returned resource records.

Theory & concepts

DNS is a distributed hierarchy. A recursive resolver asks a root server which server handles .com, asks the .com TLD server which server is authoritative for the domain, and finally asks the authoritative server for the address. Every answer is cached for its TTL.

Rendering diagram…

Recursive DNS resolution walks the hierarchy, then caches the answer.

Prerequisites

Lesson: The Domain Name System
Lesson: Application layer principles

Instructions

1Enter a domain name and start the resolution trace.
2Watch each hop: root, TLD and authoritative server.
3Inspect the resource records returned at each step.
4Identify the A record, its value and its TTL.
5Resolve a second name and compare the number of hops.
6Explain what would happen if the authoritative server were down.

Tasks

Full resolution trace
Resolve www.example.com and list every server consulted.
Identify record types
Find A and CNAME records in a trace of a name with aliases.
Caching and TTL
Re-resolve the same name and observe which answers come from the cache.
Failure analysis
Simulate a downed authoritative server and explain the timeout.

Self-check

The resolution path from root to authoritative server is traced correctly.
The student identifies A, AAAA, CNAME and NS records in output.
The role of TTL and caching is explained.
The student explains the impact of server failures on resolution.

Environment

resolver consolerecord inspectorhierarchy visualizationcache simulation