Trace a three-tier design onto a real path

applied · 45 min · Objective 1.6

Task

Take a path you can actually measure — your laptop to a service on the internet — and map each hop onto the architectural tier it represents: access, distribution, core, edge, transit. Architecture questions on the exam are disguised "where does this device sit" questions, and doing this once makes them concrete.

Steps

  1. Run traceroute -n 1.1.1.1 and save the output. Use tracert -d 1.1.1.1 on Windows.
  2. Annotate hop 1. It is your default gateway, and it is playing both the access and distribution role that a small network collapses into one box.
  3. Find the hop where the address stops being private (10.x, 172.16–31.x, 192.168.x) or carrier-grade NAT (100.64.x). That transition is your network edge — everything before it is yours, everything after is your provider's.
  4. Look up two or three of the public hops with whois and note where the organisation name changes. Each change is a peering or transit boundary.
  5. Draw the result as five or six boxes with the tier names on them. Compare your drawing with the three-tier diagram from the lesson and note what a home or small-office network collapses.

Verify

traceroute -n -m 12 1.1.1.1
ip route show default
whois $(traceroute -n -m 5 1.1.1.1 | awk 'NR>1 && $2 ~ /^[0-9]/ {print $2}' | tail -1) | grep -iE "orgname|netname|descr" | head -3

Hop 1 must equal the gateway ip route show default reports. The whois lookup must name an organisation that is not you — that is the proof you have crossed the edge rather than assumed it.

Notes

Two things commonly surprise people here. Private addresses inside your ISP's network are normal, not a misconfiguration — that is carrier-grade NAT. And asterisks in the middle of a traceroute are usually a router that declines to generate ICMP, not a broken hop; if later hops reply, the path is fine.

Keep the annotated output. Lesson 38's methodology lab asks you to reason about where a fault could be on exactly this kind of path.