8 exercises — match protocols and concepts to OSI layers, understand encapsulation, and use layer-number shorthand fluently in troubleshooting conversations.
0 / 8 completed
1 / 8
Match the layer to its function: "This layer is responsible for logical addressing and routing packets between different networks."
Layer 3 — Network handles logical addressing (IP addresses) and routing — deciding the best path for a packet across multiple networks.
The 7 OSI layers, bottom to top: 1. Physical — bits on the wire/fibre/radio (cables, voltages, radio waves) 2. Data Link — frames, MAC addresses, switches (Ethernet) 3. Network — packets, IP addresses, routers (IP, ICMP) 4. Transport — segments, ports, reliability (TCP, UDP) 5. Session — establishing, managing, tearing down sessions 6. Presentation — encoding, encryption, compression (TLS handshake formatting) 7. Application — the protocol the user-facing software speaks (HTTP, DNS, SMTP)
Mnemonic: "Please Do Not Throw Sausage Pizza Away" (bottom to top).
2 / 8
The TCP/IP model condenses the OSI model into 4 layers. Which OSI layers map onto the TCP/IP "Application" layer?
The TCP/IP model is the practical 4-layer model the real Internet is built on: Network Access (OSI layers 1–2), Internet (OSI layer 3), Transport (OSI layer 4), and Application (OSI layers 5–7 combined).
Why the difference matters in conversation: engineers say "that's an application-layer protocol" without distinguishing session/presentation concerns — in the TCP/IP model, HTTP, TLS session negotiation, and character encoding are all bundled under "Application".
Comparison table (say out loud in interviews): • OSI 7 (App) + 6 (Presentation) + 5 (Session) → TCP/IP Application • OSI 4 (Transport) → TCP/IP Transport • OSI 3 (Network) → TCP/IP Internet • OSI 2 (Data Link) + 1 (Physical) → TCP/IP Network Access
3 / 8
Fill in the blank in this packet transmission description: "As the data moves down the stack from the Application layer to the Physical layer, each layer wraps the data from the layer above with its own header — this process is called ____."
Encapsulation — each layer adds its own header (and sometimes trailer) as data passes down the stack, wrapping the payload from the layer above.
The chain, top to bottom: Data (Application) → Segment (Transport, adds TCP/UDP header with ports) → Packet (Network, adds IP header with source/destination IP) → Frame (Data Link, adds MAC header + trailer) → Bits (Physical, transmitted as electrical/optical/radio signal).
At the receiving end, the reverse happens — de-encapsulation — each layer strips off its own header and passes the remainder up to the next layer.
This vocabulary — "the packet is encapsulated with a new IP header" — is standard when describing how routers or tunnels (VPN, GRE) wrap traffic.
4 / 8
Which statement correctly places these three protocols in their OSI layers: HTTP, IP, and Ethernet?
HTTP → Application (L7), IP → Network (L3), Ethernet → Data Link (L2). Being able to state a protocol's layer fluently is a core interview and documentation skill.
More protocol-to-layer mappings worth memorising: • Application (L7): HTTP, HTTPS, DNS, SMTP, FTP, SSH • Transport (L4): TCP, UDP • Network (L3): IP, ICMP, OSPF • Data Link (L2): Ethernet, ARP, PPP, switches • Physical (L1): cables, hubs, radio (Wi-Fi's physical layer)
Note: some protocols like ARP straddle the boundary and are often described as "Layer 2.5" since they resolve Layer 3 IP addresses to Layer 2 MAC addresses.
5 / 8
A colleague says: "We're seeing the issue at Layer 2." What are they most likely troubleshooting?
Layer 2 issues relate to switching and framing within a local network segment: VLAN misconfiguration, spanning-tree loops, duplicate MAC addresses, or a bad Ethernet cable causing CRC errors.
Using layer numbers as shorthand in conversation is common professional vocabulary: • "It's a Layer 1 problem" → physical cable/port/signal issue • "It's a Layer 2 problem" → switching, VLANs, MAC tables, ARP • "It's a Layer 3 problem" → routing, IP addressing, subnetting • "It's a Layer 4 problem" → port blocking, TCP handshake failure • "It's a Layer 7 problem" → the application itself is misbehaving, even though the network is fine
This shorthand lets teams narrow down where in the stack to focus without a long explanation.
6 / 8
Which OSI layer is responsible for establishing, maintaining, and terminating a communication session between two applications (e.g., a video call staying connected while data flows both ways)?
The Session layer (L5) manages dialogue control — opening a session, keeping it synchronised, and closing it cleanly. It is one of the least discussed layers in practice because TCP/IP folds it into the "Application" layer, but it is still a useful concept for describing stateful, long-lived connections like video calls or database sessions.
Quick layer-by-layer function reference: • Physical: "how do the bits travel?" • Data Link: "how do devices on the same segment address each other?" • Network: "how does traffic find its way across networks?" • Transport: "how is delivery made reliable (or fast) and multiplexed by port?" • Session: "how is the conversation kept open and synchronised?" • Presentation: "how is the data encoded, compressed, or encrypted?" • Application: "what does the software actually want to say?"
7 / 8
Fill in the blank: "TCP operates at the ____ layer, where it adds source and destination port numbers to identify which application on the host should receive the data."
Transport layer (L4) — TCP and UDP both add port numbers so that, once a packet arrives at the correct IP address, the host knows which application (process) should receive it.
Key Transport-layer vocabulary: • Port number: identifies the application/service (e.g., 443 for HTTPS, 22 for SSH) • Segment: the unit of data at the Transport layer • Three-way handshake: SYN, SYN-ACK, ACK — establishes a TCP connection • Connection-oriented (TCP): guarantees delivery, ordering, and retransmission • Connectionless (UDP): no delivery guarantee, lower overhead, used for streaming/DNS
"The web server is listening on port 443" and "the connection was refused because nothing is listening on that port" are common ways this vocabulary appears in real troubleshooting conversations.
8 / 8
Which of these correctly explains why understanding the OSI model helps with troubleshooting, in professional English?
The OSI model's value in real teams is communication as much as technical structure. Saying "we've confirmed Layer 1–3 are fine, we suspect this is a Layer 7 application issue" instantly tells a colleague where to focus, without a long explanation.
Two common troubleshooting approaches described using OSI vocabulary: • Bottom-up: start at Physical, confirm each layer works, move upward — good when the cause is unknown • Top-down: start at Application, work downward — good when the symptom is clearly application-level (e.g., a specific web page fails but "the internet works")
Developers and SREs use this vocabulary constantly: "the health check is failing — is that an application bug (L7) or is the load balancer not routing traffic (L3/L4)?" is a standard diagnostic question in an incident channel.
What does the "OSI & TCP/IP Vocabulary — Networking Language Exercises" exercise cover?
Practise OSI 7-layer model and TCP/IP 4-layer model vocabulary in English: encapsulation, protocol-to-layer mapping, and layer troubleshooting shorthand.
Is this exercise free to use?
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How many questions are in "OSI & TCP/IP Vocabulary — Networking Language Exercises"?
This exercise has 8 questions. Each one gives instant feedback with an explanation, so you can see exactly why an answer is right or wrong.
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