✍ 04: Network Protocols — Exercises¶
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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. Describe the TCP three-way handshake, naming each message.¶
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**SYN** (client synchronizes) → **SYN-ACK** (server acknowledges + synchronizes) → **ACK** (client acknowledges). The connection is then established and data flows.🌐 Q2. For each app, choose TCP or UDP and justify: (a) VoIP call, (b) large file download, (c) DNS query, (d) live video stream.¶
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- (a) VoIP → **UDP** — low latency; a late retransmission is useless. - (b) File download → **TCP** — needs guaranteed, ordered delivery. - (c) DNS query → **UDP** — small/fast (TCP for large or zone transfers). - (d) Live video → **UDP** — real-time, tolerates minor loss.🔹 Q3. Trace the encapsulation of a web request, naming the PDU and the key header field added at Layers 4, 3, and 2.¶
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- **L4 → Segment**, adds source/destination **ports**. - **L3 → Packet**, adds source/destination **IP** (+ TTL). - **L2 → Frame**, adds source/destination **MAC** (+ FCS trailer). Then L1 sends **bits**.🔹 Q4. Match each insecure protocol to its secure replacement: Telnet, HTTP, FTP, SNMPv1.¶
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- Telnet → **SSH** - HTTP → **HTTPS** - FTP → **SFTP / FTPS** - SNMPv1 → **SNMPv3**🔹 Q5. IPsec secures VPNs. Name its two core protocols and what each provides.¶
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- **AH (Authentication Header)** — integrity/authentication. - **ESP (Encapsulating Security Payload)** — encryption (+ optional integrity). **IKE** negotiates the keys. IPsec operates at **Layer 3**.🔹 Q6. A capture shows a connection ending with an RST flag instead of FIN. What does that indicate?¶
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**RST = abrupt reset** — the connection was aborted (e.g., the port was closed or an unexpected packet arrived). **FIN** would be a **graceful** close.❓ Q7. What is a socket, and how does it uniquely identify one end of a connection?¶
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A **socket** = **IP address + port** (e.g., `192.168.1.5:443`). A pair of sockets (source + destination) uniquely identifies a TCP/UDP connection.🔹 Q8. How does TCP achieve reliable, ordered delivery?¶
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**Sequence numbers** order the bytes, **acknowledgments (ACKs)** confirm receipt, unacknowledged data is **retransmitted**, and the receiver reorders segments. The **window size** provides flow control.🔹 Q9. Which protocol powers ping and traceroute, and what field does traceroute manipulate?¶
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**ICMP**. Traceroute manipulates the **TTL** field — each router decrements TTL; when it hits 0 the router returns an ICMP "time exceeded," revealing each hop.❓ Q10. SMTP does one job; POP3/IMAP do another. What is each for, and how do POP3 and IMAP differ?¶
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- **SMTP** — **sends/relays** outgoing mail. - **POP3 / IMAP** — **retrieve** mail. POP3 typically downloads and removes mail (single device); IMAP keeps it on the server and **syncs** across devices.🔹 Q11. Which secure protocols provide (a) encrypted remote CLI, (b) remote graphical desktop, (c) encrypted file transfer over SSH?¶
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- (a) **SSH** (22) - (b) **RDP** (3389) - (c) **SFTP** (over SSH, 22)❓ Q12. What is the key difference between a connection-oriented and a connectionless protocol?¶
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**Connection-oriented (TCP)** establishes and verifies a session (handshake + ACKs) before/while sending. **Connectionless (UDP)** just sends datagrams with no setup or delivery guarantees.⬅️ Prev: Module 03 · 📚 All Exercises · Next: Module 05 — Cabling ➡️
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