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Hands-on 05-ipv4: Lab

Guided practice + break/fix + lab gate.

Show commands for:
Class 15: IPv4 addresses and gateways
Class 15 visual reference. Use it as the map, then prove it in the reading, lesson, and lab.

Overview

Module: Module 1: Infrastructure & Addressing
Activity type: Lab (Practice)
Objective: Given a host, the learner can read IPv4 address, mask, and gateway; explain network vs host bits; contrast classful charts with classless /24 math; and decide same-LAN vs via-gateway delivery.

Learn

Before you start

  • Reading complete
  • Lesson Feynman teach-back drafted (you may refine after the lab)
Hands-on

Guided lab

Use the machine you actually lab on. Replace example IPs with yours.

Path A: Read the trio and classify network vs host

1

Capture interface facts.

Windows (CMD / PowerShell)
ipconfig
ipconfig /all
Get-NetIPConfiguration | Format-List InterfaceAlias, IPv4Address, IPv4DefaultGateway
Linux / macOS (Terminal)
ip -br addr
ip route
ip -4 addr show
2

Workbook table: adapter name, IPv4, mask, gateway, DHCP or static.

3

Apply the 255/0 hack. Circle network octets vs host octets. Write one sentence: “Every host on my LAN shares _ and differs in _.”

4

List three other devices on the same LAN (phone, AP, Proxmox, printer). Confirm their IPs share the network portion you predicted (check each device’s status page or arp/ip neigh after a ping).

Linux / macOS (Terminal)
ping -c 2 GATEWAY-IP
ping -c 2 OTHER-LAN-HOST
ip neigh
Windows (CMD / PowerShell)
ping -n 2 GATEWAY-IP
ping -n 2 OTHER-LAN-HOST
arp -a

Path B: Same LAN vs via gateway

1

Same-network test: ping another LAN host; expect success (firewall permitting).

2

Off-network test: ping 1.1.1.1 (or another known Internet IP). Expect success only if WAN works.

Linux / macOS (Terminal)
ping -c 3 1.1.1.1
traceroute -n 1.1.1.1 | head
# First hop should be your default gateway on a normal home setup
ip route | awk '/default/ {print}'
Windows (CMD / PowerShell)
ping -n 3 1.1.1.1
tracert -d 1.1.1.1
# First hop should be your Default Gateway
3

Workbook: “First hop to the Internet was ____ (gateway). Local NAS ping did / did not need that hop for delivery decision.”

Path C: Usable-address math on your `/24`

1

If your mask is 255.255.255.0, compute:
- network address
- broadcast address
- theoretical host count (254)
- practical leftover after gateway (document your gateway IP)

2

Optional stretch: on the router admin UI (screenshot secrets removed), note DHCP pool start/end. Compare pool size to your math.

3

Static caution (do not break production): pick an unused address inside the subnet but outside the DHCP pool if you later static a lab VM. Record the choice; do not implement on a critical host until Class 1/Proxmox needs it.

Path D: Classes, loopback, and ping

1

Classify your LAN IP by first octet using the A–E chart. Write: class letter, default classful mask, and your actual mask. Are they the same? (Most home LANs are Class C looking with a /24 mask, or Class A looking 10.x with a classless /24.)

2

Workbook contrast: one row for “classful default size,” one row for “my real network size.” One sentence: “Classful told me _; classless/mask told me _.”

3

Loopback proof

Windows (CMD / PowerShell)
ping -n 4 127.0.0.1
ping -n 2 127.0.0.2
Linux / macOS (Terminal)
ping -c 4 127.0.0.1
ping -c 2 127.0.0.2
4

Workbook: “Loopback succeeded / failed. I would / would not assign a 127.x address to a NAS.” Circle Class D and E on the chart and write “not for unicast hosts.”

Break / fix

Break / fix

Break/fix

  1. Disconnect Wi-Fi / unplug Ethernet → ipconfig / ip addr loses address or shows disconnected → restore → address returns (DHCP) or static returns.

  2. Wrong mental model: pretend a host 10.0.0.5 is “local” to your 192.168.1.0/24 without a router, explain why the mask says no.

  3. Gateway down simulation (lab only): if you can safely shut WAN on a test router, confirm LAN pings still work while 1.1.1.1 fails, proves local vs remote paths.

  4. Class vs mask: take a 10.x address with mask 255.255.255.0 and explain to a partner why calling it “a Class A network of 16 million hosts” would be wrong for your LAN.

  5. Loopback vs LAN: with Wi-Fi off, confirm ping 127.0.0.1 still works while ping 1.1.1.1 fails, local stack vs Internet path.

Fix chart

Feedback / common mistakes

  • Mixing up private LAN IP with public WAN IP.
  • Calling every dotted number “the IP” and ignoring mask/gateway.
  • Assuming all LANs are 192.168.1.0/24.
  • Assigning .0 or .255 to a host on a /24.
  • Duplicating an IP already leased by DHCP.
  • Debugging Docker DNS before confirming the host even has a gateway.
  • Treating classful defaults as how the Internet still assigns every network (it does not, CIDR/classless won).
  • Putting a Class D/E or 127.x address on a lab host “because the chart had free numbers.”
  • Confusing “4.3 billion total IPv4 values” with “4.3 billion free for my devices.”
Hands-on

Lab gate

All boxes must be true before the next class unlocks. If you fail: feedback → targeted review → new practice → reassess.

  • [ ] Student can show IPv4, mask, and gateway from CLI or phone UI and read them aloud correctly.
  • [ ] Student marks network vs host portions using the 255/0 hack for their real LAN.
  • [ ] Same-LAN ping and Internet ping are both demonstrated (or failures explained with evidence).
  • [ ] Usable-address calculation for their /24 (or documented non-/24 with instructor help) is in the workbook.
  • [ ] Student can explain network address, broadcast address, and why the gateway consumes an address.
  • [ ] Student maps their LAN IP to a historic class, states the default mask, and contrasts it with the real mask (classful vs classless).
  • [ ] Student demonstrates ping 127.0.0.1 and explains why 127.0.0.0/8 is not LAN address space.
  • [ ] Student names Class D (multicast) and Class E (reserved) as non-assignable for ordinary hosts.
  • [ ] No home street address, no real public IP doxxing, and no secrets in shared screenshots.
  • [ ] Prior-knowledge check answered
  • [ ] Feynman teach-back completed (Explain, Simplify, Example, Weak spot, Retry)
  • [ ] Independent practice completed
  • [ ] Retrieval check attempted (target ≥80% when scored)
  • [ ] Evidence recorded in workbook / verification matrix
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