Predict what a VPN changes, then verify each prediction

short · 40 min · Objective 2.2

Task

Write down what you expect a VPN to change about a machine's view of the network, then measure each one -- because the surprises are where the model is wrong, and the model is what answers the exam's scenario questions.

Steps

  1. BEFORE connecting, write lab/vpn/predictions.csv with header item,before,predicted_after covering: apparent public address, default gateway, configured DNS servers, reachability of a device on your own local network, and the route table's default entry.
  2. Capture the actual before-state for each item into lab/vpn/before.txt.
  3. Connect, capture the after-state into lab/vpn/after.txt, and fill lab/vpn/actual.csv with header item,before,after,matched.
  4. Record in lab/vpn/tunnel.md whether the connection is split or full tunnel, and state the evidence -- the route table, not the vendor's description.
  5. Disconnect, confirm the before-state returns, and record it in lab/vpn/restored.txt. Where you had no VPN available, write lab/vpn/skipped.md naming which steps were not run and why.

Verify

These checks run in a POSIX shell: Terminal on macOS or Linux, and on Windows Git Bash (it comes with Git for Windows) or WSL. A stock Windows PowerShell or Command Prompt has no awk or grep, so there the first line fails.

awk -F, 'NR>1 && NF>=3 {n++} END {print n" prediction(s)"}' lab/vpn/predictions.csv
test -s lab/vpn/before.txt && echo "before captured"
if test -s lab/vpn/actual.csv; then
  awk -F, 'NR>1 && NF>=4 {n++} END {print n" item(s) compared"}' lab/vpn/actual.csv
  grep -Eic 'split|full' lab/vpn/tunnel.md
elif test -s lab/vpn/skipped.md; then
  echo "skip documented"
else
  echo "NEITHER a comparison nor a documented skip"
fi

Five predictions written before any measurement, a captured before-state, and either a completed comparison or a documented skip. A lab that cannot be run completely should say so precisely rather than be reported as done.

Notes

The prediction file must be written first. Filling it in after the measurement turns a test of your model into a transcription exercise, and the whole value here is finding out where the model was wrong.

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