✍ 03: Addressing — Exercises¶
Tip
Practice — try each question first, then expand the answer to check your reasoning.
Work through each question, then click ▶ Show answer to check yourself. Review the notes if you get stuck.
🔹 Q1. How many bits is a MAC address, how is it written, and what does its first half identify?¶
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**48 bits**, written as six pairs of hex digits (e.g., `00:1A:2B:3C:4D:5E`). The first 24 bits are the **OUI** identifying the NIC **manufacturer**; the last 24 bits are device-specific.🔹 Q2. Classify each address as public, private, loopback, or APIPA: 10.24.5.9, 8.8.8.8, 169.254.13.7, 127.0.0.1, 172.20.0.1, 192.168.100.5.¶
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- `10.24.5.9` → **Private** (10.0.0.0/8) - `8.8.8.8` → **Public** - `169.254.13.7` → **APIPA** (169.254.0.0/16 — DHCP failed) - `127.0.0.1` → **Loopback** - `172.20.0.1` → **Private** (172.16.0.0/12) - `192.168.100.5` → **Private** (192.168.0.0/16)🔹 Q3. A workstation shows IP 169.254.44.10. What happened, and what should you check?¶
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The host **failed to reach a DHCP server** and self-assigned an **APIPA** address. Check: is the DHCP server up? cable/link OK? correct VLAN? Does the subnet need a **DHCP relay** (`ip helper-address`)?📡 Q4. List the DHCP DORA process and the ports DHCP uses.¶
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**D**iscover → **O**ffer → **R**equest → **A**ck. Ports: server **UDP 67**, client **UDP 68**.🌐 Q5. Give the port and transport (TCP/UDP) for: HTTPS, DNS, SSH, SMTP, RDP.¶
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- HTTPS → **443/TCP** - DNS → **53/UDP** (TCP for zone transfers / large responses) - SSH → **22/TCP** - SMTP → **25/TCP** - RDP → **3389/TCP**🌐 Q6. Which DNS record type maps a name to an IPv4 address? To an IPv6 address? What does an MX record do?¶
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- **A** → name to IPv4 - **AAAA** → name to IPv6 - **MX** → identifies the domain's mail server(s) (with a priority value)🌐 Q7. Compress the IPv6 address 2001:0db8:0000:0000:00a3:0000:0000:1f35.¶
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`2001:db8::a3:0:0:1f35` Drop leading zeros; replace the **longest** run of all-zero hextets (`0000:0000`, hextets 3–4) with `::`. The later `0:0` can't also use `::` (only one `::` allowed).🔹 Q8. A host can ping 8.8.8.8 but cannot open https://example.com. What's the likely cause, and which command confirms it?¶
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IP connectivity works but name resolution fails → a **DNS problem**. Confirm with **`nslookup example.com`** (or `dig`).❓ Q9. What is the default subnet mask for a /24, and how many usable hosts does it provide?¶
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**255.255.255.0**; 2^8 − 2 = **254** usable hosts.🌐 Q10. What protocol resolves an IP to a MAC on the local segment, and what replaces it in IPv6?¶
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**ARP** (Address Resolution Protocol) in IPv4. In IPv6, **NDP** (Neighbor Discovery Protocol, built on ICMPv6) performs the equivalent function.❓ Q11. What is the difference between a DHCP reservation and an exclusion?¶
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- **Reservation** — binds a specific **MAC** to always receive the same IP from the pool. - **Exclusion** — removes addresses from the pool so they are never handed out (e.g., reserved for static devices like the gateway).❓ Q12. Which minimum three settings does a host need to communicate with hosts on other networks, and what is each for?¶
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- **IP address** — the host's own address. - **Subnet mask** — tells it which addresses are local. - **Default gateway** — where to send traffic destined for other networks. (DNS is additionally needed to resolve names.)⬅️ Prev: Module 02 · 📚 All Exercises · Next: Module 04 — Network Protocols ➡️
🧭 Bonus Scenario Practice¶
🧩 Case A: DHCP Scope Conflict¶
A small office uses 192.168.50.0/24. The router is 192.168.50.1, printers are statically assigned .20 through .30, and the DHCP scope gives out .10 through .200. Several users randomly lose printer access after rebooting laptops. What is the likely cause and fix?
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The DHCP scope overlaps with the statically assigned printer range. A client can receive an address already used by a printer, causing an IP conflict. Fix it by excluding `.20` through `.30` from the DHCP scope, or moving static infrastructure addresses outside the dynamic pool.🧩 Case B: Wrong Gateway¶
A host has IP 10.20.30.45/24, DNS 10.20.30.10, and gateway 10.20.40.1. It can ping another host on 10.20.30.0/24 but cannot reach the Internet. What is wrong?