Episode 1 — Fundamentals / 1.1 — How The Internet Works

1.1 — Exercise Questions: How the Internet Works

Practice questions for all five subtopics in Section 1.1. Mix of short-answer, diagram, and hands-on exercises. Try each without peeking at the hints first.

How to use this material (instructions)

  1. Read lessons in order — README.md, then 1.1.a → 1.1.e.
  2. Answer closed-book first — only open hints after a real attempt.
  3. Hands-on — actually run suggested commands (dig, curl, DevTools); passive reading is not enough.
  4. Redo misses — retry wrong items the next day.
  5. Interview prep — pair with 1.1-Interview-Questions.md for polished model answers.

1.1.a — History of the Web (Q1–Q8)

Q1. Name the three technologies Tim Berners-Lee invented that form the foundation of the web. For each, write one sentence explaining what it does.

Q2. Exercise: Draw a timeline on paper with at least 8 key dates between 1969 and 2020. For each, write the event and why it mattered.

Q3. Explain the difference between the Internet and the World Wide Web in your own words. Give two examples of services that run on the internet but are NOT part of the web.

Q4. Compare Web 1.0, Web 2.0, and Web 3.0 by filling out a table with these rows: Mode (read/write/own), Content type, Architecture (centralized/decentralized), Example platform, Business model.

Q5. Why was CERN's decision to release the WWW into the public domain in 1993 so important? What might have happened if they had patented it instead?

Q6. What problem was Tim Berners-Lee trying to solve at CERN? Why couldn't existing systems (email, FTP) solve it adequately?

Q7. Name three iconic websites or services from each era: Web 1.0, Web 2.0, and Web 3.0 (nine total).

Q8. Scenario: A friend says "Web 3.0 will completely replace Web 2.0 like Web 2.0 replaced Web 1.0." Is this accurate? Explain why the versions layer rather than replace.

1.1.b — How Computers Communicate (Q9–Q18)

Q9. List all 7 layers of the OSI model from bottom (Layer 1) to top (Layer 7). For each, name one protocol or technology that operates at that layer.

Q10. What is the mnemonic for remembering the OSI layers? Write it out and match each word to its layer.

Q11. Exercise: Draw the TCP/IP 4-layer model side by side with the OSI 7-layer model. Draw arrows showing which OSI layers map to which TCP/IP layers.

Q12. Explain encapsulation in 3–4 sentences. What happens to data as it moves DOWN the protocol stack from Application to Physical?

Q13. Explain the TCP 3-way handshake step by step. What flags are set in each packet (SYN, ACK)? Why are 3 steps needed instead of 2?

Q14. Compare TCP and UDP. Create a table with columns for: Connection type, Reliability, Ordering, Speed, Overhead, Use cases (at least 3 each).

Q15. What is a port number? Why do we need ports in addition to IP addresses? List at least 8 well-known ports and their services from memory.

Q16. What is the difference between the client-server model and peer-to-peer? Give two real-world examples of each.

Q17. What is a PDU (Protocol Data Unit)? Name the PDU at each layer: Application, Transport, Network, Data Link, Physical.

Q18. Hands-on: Open a terminal and run netstat -an (or ss -tuln on Linux). Identify at least 3 listening ports on your machine and guess which service each belongs to.

1.1.c — How Data Travels Worldwide (Q19–Q28)

Q19. What percentage of international internet traffic travels through submarine cables? Why are satellites not the primary method for bulk internet traffic?

Q20. Describe the cross-section of a submarine cable. Name at least 4 layers from outside to inside and explain the purpose of each.

Q21. What is DWDM (Dense Wavelength Division Multiplexing) and why is it important for fiber optic capacity? Explain in plain English.

Q22. What is a repeater in the context of submarine cables? How often are they placed, and how are they powered?

Q23. Exercise: Explain how a 1 MB image is transmitted over the internet. Calculate how many packets are needed (assume MTU of 1,500 bytes and IP/TCP header overhead of 40 bytes). Show your math.

Q24. What is the difference between circuit switching (old phone system) and packet switching (the internet)? Which is more efficient for internet traffic, and why?

Q25. Explain what a routing table is and how routers make forwarding decisions. What is a default route?

Q26. Name and briefly describe three routing protocols: BGP, OSPF, and RIP. Which one connects ISPs to each other?

Q27. What is an Internet Exchange Point (IXP)? Why do they make the internet faster and cheaper? Name at least 2 major IXPs.

Q28. Hands-on: Run traceroute google.com (macOS/Linux) or tracert google.com (Windows). Count the hops. Identify which hops are your local network, your ISP, and the destination network.

1.1.d — Domain Names, IP & MAC Addresses, Routing (Q29–Q40)

Q29. Break down the URL https://blog.example.co.uk:8443/articles/hello?lang=en#intro into all its parts: scheme, subdomain, SLD, TLD, port, path, query string, fragment.

Q30. What is the difference between a generic TLD (.com, .org) and a country-code TLD (.uk, .jp)? Name 3 examples of each.

Q31. Compare IPv4 and IPv6. Create a table with rows for: Address size, Format/notation, Total addresses, NAT requirement, Header complexity, Example address.

Q32. What are the three private IP address ranges defined in RFC 1918? Write them in CIDR notation and state how many addresses each range contains.

Q33. What is 127.0.0.1? What is 0.0.0.0? What is 169.254.x.x? Explain each special address.

Q34. Explain the difference between a MAC address and an IP address. At which OSI layer does each operate? Which one changes at every router hop, and which stays the same end-to-end?

Q35. Exercise: A packet travels from your laptop through 3 routers to a server. Fill in a table showing the Source MAC, Dest MAC, Source IP, and Dest IP at each hop. Which values change and which stay the same?

Q36. What is NAT (Network Address Translation)? Draw a simple diagram showing 3 devices with private IPs sharing one public IP through a router. Explain how the router tracks which response belongs to which device.

Q37. What is ARP (Address Resolution Protocol)? Describe the 3-step process: ARP Request (broadcast), ARP Reply (unicast), ARP Cache.

Q38. What does /24 mean in CIDR notation? How many total IP addresses and usable host addresses does a /24 subnet have? Why are 2 addresses unusable?

Q39. Exercise: Given the network 10.0.0.0/8, calculate: total addresses, usable hosts, network address, and broadcast address.

Q40. Hands-on: Run arp -a on your machine. What devices appear? Can you identify your router's MAC address? Run ifconfig (macOS/Linux) or ipconfig /all (Windows) and find your own MAC and IP addresses.

1.1.e — ISP and DNS (Q41–Q52)

Q41. What are the three tiers of ISPs? For each tier, explain their role and give an example.

Q42. What is the difference between transit and peering in the context of ISP interconnection?

Q43. Exercise: Draw the complete DNS resolution process for www.github.com. Include all 7 steps: browser cache, OS cache, recursive resolver, root server, TLD server, authoritative server, and the response path back.

Q44. Name at least 6 DNS record types and explain what each one does (A, AAAA, CNAME, MX, NS, TXT, SOA, PTR, SRV — pick any 6).

Q45. What is TTL (Time To Live) in DNS? Why would a site use a low TTL (e.g., 60 seconds) vs a high TTL (e.g., 86400 seconds)?

Q46. Describe the 4 levels of DNS caching. At which level is caching most impactful for reducing DNS traffic?

Q47. What is DHCP? Describe the 4-step DORA process (Discover, Offer, Request, Acknowledge). What 4 pieces of information does your device receive?

Q48. Compare ISP DNS with public DNS providers (Google 8.8.8.8, Cloudflare 1.1.1.1, Quad9 9.9.9.9). List at least 2 pros and 2 cons of switching from ISP DNS to a public provider.

Q49. What is DNS spoofing (cache poisoning)? How does DNSSEC protect against it?

Q50. What is the difference between DNS-over-HTTPS (DoH) and DNS-over-TLS (DoT)? What problem do both solve that regular DNS does not?

Q51. Hands-on: Use dig google.com or nslookup google.com to look up a domain. Identify the IP address, TTL, and which name server answered. Try dig google.com MX to see mail server records.

Q52. Hands-on: Use dig +trace google.com to see the full DNS resolution chain from root to authoritative. Identify each server in the chain and the record type returned at each step.

Comprehensive Exercises (Q53–Q60)

Q53. Mega-Exercise: Write a complete narrative (at least 15 steps) of what happens when you type https://www.amazon.com and press Enter — from URL parsing to the rendered page. Cover: URL parsing, HSTS, DNS, TCP handshake, TLS handshake, HTTP request, server processing, HTTP response, rendering pipeline. Reference concepts from all 5 sub-topics.

Q54. Diagram Exercise: Draw the physical path of a packet traveling from your laptop in London to a server in San Francisco. Include: your Wi-Fi router, ISP local node, ISP backbone, submarine cable landing station, transatlantic cable, US landing station, IXP, destination ISP, and the server's data center.

Q55. Comparison Exercise: Create a master comparison table for: Domain Name vs IP Address vs MAC Address. Rows: Layer, Scope, Format, Who assigns it, Does it change?, Survives routing?, Analogy.

Q56. Calculation Exercise: Light travels through fiber at ~200,000 km/s. The submarine cable distance from London to New York is approximately 6,000 km. Calculate the minimum one-way latency and round-trip time (RTT). Why is real-world RTT higher than this theoretical minimum?

Q57. Scenario: Your website is down. Users report "DNS_PROBE_FINISHED_NXDOMAIN" in their browsers. What does this error mean? List 5 possible causes and the steps you would take to diagnose each one.

Q58. Scenario: You run traceroute to a remote server and notice latency jumps from 20ms to 180ms at hop #5. What might be happening at that hop? Name 3 possible explanations.

Q59. Explain-It Marathon: Without notes, explain each of the following in under 30 seconds each:

  1. The difference between the internet and the web
  2. What TCP's 3-way handshake does
  3. Why data is split into packets
  4. What NAT does
  5. The DNS resolution chain (7 steps)

Q60. Build Exercise: Set up a simple web server on your local machine (using Python: python3 -m http.server 8080 or Node.js). Access it from your browser at http://localhost:8080. Then use curl -v http://localhost:8080 and identify the request line, response status, and at least 3 headers.

Answer Hints

(Short reminders — expand in your own words when studying.)

QHint
Q1HTML (structure), HTTP (transfer protocol), URL (addressing).
Q21969 ARPANET, 1971 email, 1983 TCP/IP, 1989 WWW proposal, 1990 first browser, 1991 public, 1993 public domain, 1995 JS.
Q3Internet = global network infrastructure; Web = service on top (HTTP/HTML). Email (SMTP), FTP are non-web internet services.
Q41.0: read/static/decentralized/GeoCities/banner ads. 2.0: read-write/dynamic/centralized/Facebook/ads. 3.0: own/user-owned/decentralized/Ethereum/tokens.
Q5Free access enabled explosive growth. Patent = licensing fees per page view would have killed adoption.
Q6Scientists used incompatible systems. Email lacks hyperlinks; FTP requires knowing exact paths. He wanted universal linked documents.
Q9Physical, Data Link, Network, Transport, Session, Presentation, Application.
Q12Each layer adds its own header. Data → Segment (TCP hdr) → Packet (IP hdr) → Frame (L2 hdr+trailer) → Bits.
Q13SYN (client→server), SYN-ACK (server→client), ACK (client→server). 3 steps needed so both sides agree on sequence numbers.
Q14TCP: connection-oriented, reliable, ordered, slower, higher overhead, web/email/file. UDP: connectionless, unreliable, unordered, faster, lower overhead, gaming/video/DNS.
Q15Port = apartment number on an IP building. HTTP=80, HTTPS=443, SSH=22, DNS=53, SMTP=25, FTP=21, MySQL=3306, PostgreSQL=5432.
Q19~95%+. Satellites have higher latency (~600ms vs ~60ms) and lower bandwidth.
Q21Multiple wavelengths (colors) of light on one fiber, each carrying independent data. Multiplies capacity enormously.
Q231,000,000 bytes / (1500 - 40) bytes = ~685 packets.
Q24Circuit: dedicated path held for entire session (wasteful). Packet: shared path, packets routed independently (efficient).
Q29scheme=https, subdomain=blog, SLD=example, TLD=co.uk, port=8443, path=/articles/hello, query=lang=en, fragment=intro.
Q31IPv4: 32-bit, dotted decimal, 4.3B, NAT needed, variable header, 192.168.1.1. IPv6: 128-bit, hex:colon, 340 undecillion, no NAT needed, fixed header, 2001:db8::1.
Q3210.0.0.0/8 (16.7M), 172.16.0.0/12 (1M), 192.168.0.0/16 (65K).
Q34MAC = L2, local, hardware-burned, changes each hop. IP = L3, global, assigned by DHCP/admin, stays same end-to-end.
Q36Router maps (private IP:port) ↔ (public IP:port) in a NAT table. Uses port numbers to track which internal device gets each response.
Q38/24 = first 24 bits are network. 256 total, 254 usable. Network address (first) and broadcast address (last) are reserved.
Q41Tier 1: global backbone (Lumen). Tier 2: regional (Vodafone). Tier 3: local last-mile (your cable company).
Q42Transit = paying for traffic routing ($$). Peering = free mutual exchange at IXP.
Q45Low TTL: fast failover/load balancing changes. High TTL: less DNS traffic, faster for users, but slower to propagate changes.
Q47DORA: Discover (broadcast), Offer (server proposes), Request (client accepts), Acknowledge (server confirms). Gets: IP, subnet mask, gateway, DNS servers.
Q49Attacker injects fake DNS responses redirecting to malicious site. DNSSEC signs records cryptographically so forgeries are detected.
Q53Cover: URL parse → HSTS → cache → DNS (7 steps) → TCP 3-way → TLS handshake → HTTP GET → server LB/proxy/app/DB → HTTP 200 + HTML → DOM/CSSOM → layout → paint → composite → subresource fetches.
Q56One-way: 6000 / 200000 = 0.03s = 30ms. RTT: 60ms. Real-world higher due to: non-straight cable path, router processing, queuing, protocol overhead.

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