The Computer Networks sheet walks the stack: the link layer, IP addressing and routing, TCP and congestion control, the application layer with HTTP and DNS, wireless, and network security.
The sheet holds 10 patterns and 50 topics, tracked row by row. From any row you can read the theory for a topic, answer knowledge-check questions on it, have the AI coach teach it back to you, keep notes, bookmark a row and mark it done. Progress is saved against your account, so the sheet is also the record of what you have already covered.
Who it is for
It is for candidates facing a networking or systems fundamentals round, and for engineers who want to explain a latency graph rather than describe it.
How to work through it
Follow one request end to end and keep asking what happens next. Naming the layers earns little; tracing a page load from DNS through the TCP handshake to the first byte demonstrates the same knowledge and answers the question that is actually asked.
Practice runs on the same platform as the sheet: 850+ problems across every track, code execution in 6 languages, and AI mock interviews that follow the pattern you are studying rather than a random question.
What the computer networks sheet covers
Interview Soon
5 patterns, 25 topics — the ones that come up first
Network Fundamentals — What a Network Is and How the Internet Is Built, Packet Switching and Circuit Switching, Delay, Loss and Throughput, Protocol Layers and Encapsulation, Network Topologies and Performance Basics
The Physical and Link Layers — Transmission Media and Signals, Framing and Error Detection, Multiple Access Protocols, Ethernet, Switches and MAC Addresses, ARP and Getting a Frame to the Next Hop
The Network Layer and IP — What the Network Layer Does, IPv4 Addressing, Subnetting, The IP Datagram, Fragmentation and ICMP, NAT, DHCP and IPv6
Routing — Forwarding Tables and Longest Prefix Match, Distance Vector Routing, Link State Routing and Dijkstra's Algorithm, Hierarchical Routing and BGP, Broadcast, Multicast and Routing in Practice
The Transport Layer — Transport Layer Services and Multiplexing, UDP, Principles of Reliable Data Transfer, TCP Connections and Segment Structure, TCP Reliability and Flow Control
Deep Dive
5 patterns, 25 topics for full coverage
Congestion Control — What Congestion Is, TCP Congestion Control, Fairness and Efficiency, Queue Management and Delay, Comparing TCP and UDP in Practice
The Application Layer — Application Architectures and Sockets, HTTP and the Web, DNS, Email and File Transfer, Peer-to-Peer and Content Distribution
Wireless and Mobile Networks — What Makes Wireless Different, WiFi and 802.11, Cellular Networks, Mobility Management, Wireless Performance and TCP over Wireless
Network Security — Security Goals and Cryptography Basics, Integrity, Hashes and Digital Signatures, Authentication and Key Distribution, TLS and Securing a Connection, Attacks and Defences
Putting the Layers Together — What Happens When You Load a Web Page, Following a Packet Through the Layers, Diagnosing Common Network Problems, Network Performance and Design Tradeoffs, How the Layers Compare and Where Each Function Lives
Reference: 40 questions
Last updated: September 1, 2026 · drawn from 238 computer networks knowledge-check questions, free on every plan.
Network Fundamentals
What is the difference between the edge and the core?
The edge contains end systems that run applications; the core contains routers and links that forward packets.
What happens if 11 packet-switched users simultaneously need 100 kbps on that link?
Their demand is \(11\times100=1.1\) Mbps, exceeding the 1 Mbps capacity, so packets must queue or some may be dropped.
A link is 500 km long. Does sending a larger packet increase its propagation delay?
Answer: No. Propagation delay is distance divided by signal speed. A larger packet increases transmission delay.
What is inside an Ethernet frame in this example?
An IPv4 datagram, which contains a TCP segment, which contains the application message.
The Physical and Link Layers
A channel has \(B=2\text{ MHz}\) and two noiseless signal levels. What is its Nyquist limit?
\(R=2(2\text{ MHz})\log_2 2=4\text{ Mb/s}\).
If a flag byte is `7E`, how is data byte `7E` sent when the escape byte is `7D`?
It is sent as `7D 7E`; the receiver removes the escape byte.
What is the difference between TDMA and FDMA?
TDMA separates devices by time slots; FDMA separates them by frequency bands.
The destination MAC is absent from the switch table. What happens?
The switch floods the frame through every port except the incoming port.
The Network Layer and IP
What process determines that Network C should be reached through Network B?
Routing, because it determines paths across the network.
What are the network and broadcast addresses for `10.2.3.0/24`?
The network address is `10.2.3.0`; the broadcast address is `10.2.3.255`.
How many usable addresses does a `/27` provide in the usual case?
Answer: `2^(32-27) - 2 = 32 - 2 = 30`.
What does a fragment offset of 185 mean?
The fragment’s payload begins at byte \(185\times8=1,480\) of the original payload.
Routing
Why does `0.0.0.0/0` match an address such as `8.8.8.8`?
Its prefix length is zero, so it requires no matching initial bits.
Why does a router not need the complete topology?
Answer: It can calculate a route through each neighbour using the neighbour’s advertised distance.
When does Dijkstra finalise a node?
It finalises the unfinalised node with the smallest tentative distance.
What is the difference between intra-AS and inter-AS routing?
Intra-AS routing chooses paths within one organisation, usually for efficiency. Inter-AS routing chooses paths between organisations, primarily according to policy.
The Transport Layer
Why can two TCP clients both use source port `50000` when connecting to one server?
Their source IP addresses can differ, so their TCP four-tuples differ.
Which field lets a host deliver an arriving datagram to the correct local program?
The destination port, which the operating system uses to select the receiving socket.
What prevents a retransmitted packet from being delivered twice?
The receiver checks its sequence number against the packet it expects and discards an already accepted number.
A TCP segment has `seq=900` and carries 200 bytes. What is the next expected byte?
`1100`, because the segment contains bytes `900` through `1099`.
Congestion Control
What happens to throughput after offered load passes saturation?
It first flattens, then can fall because retransmissions consume capacity. That fall is congestion collapse.
With `cwnd = 1` and no loss, what are the next three round-based window values during slow start?
2, 4, and 8 MSS.
What does the equal-share line represent?
It represents points where the two competing connections have equal rates.
What does drop-tail do when a buffer is full?
It discards the newly arriving packet.
The Application Layer
A UDP server receives a datagram from `198.51.100.7:50000`. How can it reply?
It passes that address to `sendto` as the reply destination.
What is the difference between a request body and a response body?
A request body carries data from client to server; a response body carries returned data from server to client.
What does a root server return when asked for `www.example.com`?
Normally a referral to the `.com` nameservers, rather than the final IPv4 address.
Which protocol normally keeps messages and read flags synchronized across devices?
IMAP.
Wireless and Mobile Networks
Why does carrier sensing fail for hidden terminals?
Because the two senders cannot hear one another, even though both signals reach the receiver.
What happens after a station finds an idle channel?
It waits DIFS, counts down a random backoff while the channel stays idle, and transmits when the counter reaches zero.
What changes during a handover?
The device’s serving base station changes; the network aims to preserve its active packet session and IP reachability.
Which address remains in the existing TCP connection?
The home address, such as `10.0.0.7`.
Network Security
Alice wants Bob to know that a message came from Alice. Which key does Alice use for a digital signature?
Alice uses her private key; Bob verifies with Alice’s public key.
What secret does Bob need to verify a MAC?
Bob needs the shared secret key.
What changes when the server sends nonce `314` and later nonce `802`?
The correct HMAC response changes because it is computed over the current nonce; the old response is no longer valid.
What does the certificate let the client verify?
It lets the client check that the public key belongs to the requested server name through a trusted CA signature and related checks.
Putting the Layers Together
The web server is `93.184.216.34`, but the gateway is `192.168.1.1`. Which IP does ARP resolve?
ARP resolves the gateway’s IP to the gateway’s MAC because the web server is remote.
What destination MAC does the client use when the server is beyond a router?
The MAC address of the router’s client-side interface, because the router is the next local hop.
The gateway and `8.8.8.8` both reply, but `example.com` cannot be resolved. What is the likely problem?
DNS resolution.
How long does 100 MB take at 5 Mb/s, ignoring protocol setup?
\(800\text{ Mb}/5\text{ Mb/s}=160\) seconds.
Limited time — 15% off all plans & roadmaps Use code
