Break name resolution five ways and find each one from the symptom

applied · 80 min · Objective 2.1

Task

Create five distinct resolution faults on your own machine, one at a time, and prove that each can be identified from its symptom plus one command -- then revert every one and confirm it.

Steps

  1. Record the working baseline in lab/dns/baseline.txt: the configured resolvers, a successful lookup, and a successful connection.
  2. Create five faults, one at a time, reverting each before the next: an entry in the hosts file pointing a name you control at the wrong address; no resolver configured; a resolver address that is unreachable; a stale cached answer after a hosts file change; and a query for a name that does not exist.
  3. For each, record in lab/dns/faults.csv with header fault,symptom,command_that_found_it,output_signature,seconds.
  4. For at least two faults, query a specific resolver directly and record in lab/dns/direct.md how the answers differed between your configured resolver and the direct query.
  5. Revert everything, confirm the baseline behaviour returns, and record the confirmation in lab/dns/reverted.txt with one line per fault.

Verify

grep -c . lab/dns/baseline.txt
awk -F, 'NR>1 && NF>=5 {n++} END {print n" fault(s) recorded"}' lab/dns/faults.csv
awk -F, 'NR>1 {print $3}' lab/dns/faults.csv | sort -u | wc -l
grep -c . lab/dns/direct.md
grep -c . lab/dns/reverted.txt

Five faults with a symptom and a finding command each, at least two distinct commands used, the direct-query note present, and five revert confirmations. If one command found all five, the faults were not distinct enough.

Notes

The hosts file entry is the one worth remembering. It overrides everything, never expires, and an unexpected entry on a user's machine is a finding rather than a curiosity.

This is an independent study companion for CompTIA A+ Core 1 220-1201 and is not produced by or endorsed by CompTIA.