Networking — MCQs & Practice Questions

A LAN covers a small geographical area such as one building and its hardware is usually owned by the organisation. A WAN covers a large area and typically uses third-party communication links.

An IP address identifies a device on a network and can change when the device moves to a different network. A MAC address is fixed in the hardware and uniquely identifies the network adapter itself.

The data is divided into equal-sized blocks. Each packet carries a header with the source and destination addresses and its sequence number, and packets may travel by different routes and are reassembled in order at the destination.

1. A LAN[1]
2. The computers are all within a single building and the school owns the cabling[1]
3. A switch connects devices within the LAN[1]
4. It forwards each frame only to the port of the intended recipient, using MAC addresses[1]
5. A router connects the LAN to another network, usually the internet[1]
6. It forwards packets between networks using IP addresses[1]
7. Advantage: files and printers can be shared[1]
8. Advantage: software and backups can be managed centrally[1]

1. The browser sends the domain name to a DNS server[1]
2. The server looks up the matching IP address[1]
3. The IP address is returned and the browser requests the page from that server[1]
4. HTTPS encrypts the data in transit, HTTP sends it in plain text[1]
5. So HTTPS protects information such as passwords from being read if intercepted[1]
6. To block access to unsuitable or unauthorised sites[1]
7. To inspect incoming traffic and block unauthorised access to the network[1]

1. Faster and more reliable, with less interference[1]
2. Devices can be moved freely and no cabling is needed[1]
3. Use WPA encryption on the wireless network[1]
4. Data sent over the air is scrambled[1]
5. So anyone intercepting the signal cannot read it without the keyaccept MAC filtering or a strong passphrase, explained[1]

The internet is the global infrastructure of interconnected networks that carries data. The world wide web is a collection of pages and resources accessed over that infrastructure — one of several services using it, alongside email and file transfer.

It translates a domain name that people can remember into the IP address the network needs to route data. This also allows a site to move to a different server without its address changing for visitors.

Keeping a user logged in as they move between pages of a site, and remembering preferences such as language, currency or the contents of a shopping basket.

1. The browser extracts the domain name and requests its IP address from a DNS server[1]
2. The DNS server returns the IP address, querying other DNS servers if necessary[1]
3. The browser sends an HTTP request to that address and the server responds with the HTML[1]
4. The browser requests the further resources the page references, then parses the HTML, applies the CSS and renders the page[1]

DNS lookup → HTTP request → server response → further resource requests → parse and render.

1. The data is encrypted in the browser before it is transmitted[1]
2. so anyone intercepting it on the network sees only ciphertext and cannot read the card details[1]
3. A digital certificate issued by a trusted authority supplies the public key and confirms the site's identity[1]
4. The padlock does not guarantee the site is honest — only that the connection is encrypted and the site is genuinely the one named on the certificatea fraudulent site can hold a valid certificate[1]

Encryption in transit plus a certificate proving identity; the padlock says nothing about the site's honesty.

1. A session cookie is held in memory and deleted when the browser closes — used to keep the customer logged in while moving between pages[1]
2. A persistent cookie is stored on disk and survives until it expires — used to remember preferences or a basket between visits[1]
3. A cookie set by an advertiser present on many different sites can be read on each of them[1]
4. so a record of the user's browsing can be assembled across sites without their being aware of itthe cross-site point is the concern[1]
5. A cookie is a small text file, not a program, so it cannot be executed[1]
6. It can only be read by the site that set it, and cannot access other files on the machine — the genuine risk is to privacy, not to the computer[1]

(a) session in memory until the browser closes; persistent on disk until expiry (b) cross-site tracking builds a browsing profile (c) it is data, not a program

Any two of: the sender's address, the receiver's address, the packet number, and the total number of packets making up the file.

The bits travel at very slightly different speeds along different wires, so they arrive out of step — a problem called skew — and the data can no longer be read correctly. Long parallel cables also suffer crosstalk between adjacent wires.

A keyboard to a computer: data travels from the keyboard to the machine and never in the other direction, so only one direction is ever used.

1. The file is divided into packets, each with a header containing the addresses and its packet number[1]
2. Packets travel independently and may take different routes; the receiver reassembles them in order using the packet numbers[1]
3. Advantage: a single corrupted or lost packet can be resent on its own rather than restarting the whole file[1]
4. Advantage: many transfers share the same links, and a broken route can be avoided rather than stopping transmission[1]

Split into numbered packets, routed independently, reassembled by number — allowing resends and rerouting.

1. (i) Serial — USB sends one bit at a time[1]
2. (i) Full duplex in modern versions — data is read and written in both directionsaccept half duplex for USB 1 and 2 with justification[1]
3. (ii) Serial and half duplex — one party speaks at a time[1]
4. (iii) Parallel, because the distance is very short, and full duplexinside the machine skew is not a problem[1]

(i) serial full duplex (ii) serial half duplex (iii) parallel

1. The distances between rooms are far too great for parallel transmission[1]
2. Skew and crosstalk would corrupt the data, and serial also needs fewer wires so the cabling is cheaper[1]
3. USB is a universal standard, so one type of connector serves many different devices[1]
4. The connector cannot be inserted the wrong way round, and devices are detected automatically with drivers loaded — plug and play[1]
5. It also supplies power as well as data, so small peripherals need no separate supplyany three advantages[1]
6. The error-checking value in the trailer fails, so the receiver requests that packet again — only the one packet is resent, not the whole filethe point is that just one packet is affected[1]

(a) skew and crosstalk over distance (b) universal, one-way connector, plug and play, supplies power (c) that packet alone is requested again

One bit of each byte is set so that the total number of 1s is even. The receiver counts the 1s in the byte it received; if the total is odd, at least one bit has been corrupted in transmission.

If two bits flip in the same byte, the parity is restored and the error is not detected. It also cannot identify which bit is wrong, so the data must be resent rather than repaired.

An extra digit calculated from the others and appended to a code such as an ISBN, barcode or account number, so that a data entry error can be detected immediately when the code is typed in.

1. Each byte carries a parity bit, so a corrupted byte fails its own row check[1]
2. An extra parity byte is sent whose bits give the parity of each column across the block[1]
3. A single flipped bit causes exactly one row and exactly one column to fail their checks[1]
4. The bit at the intersection of that row and column is the faulty one, so it can simply be flipped back — no resend is neededthe intersection is the key idea[1]

The failing row and failing column intersect at the corrupted bit, which is then flipped back.

1. The receiver checks each packet using an error-detection method such as a checksum[1]
2. It sends back a positive acknowledgement if the packet is intact, or a negative one if it is corrupted, prompting a resend[1]
3. The sender starts a timer when it transmits each packet[1]
4. If no acknowledgement arrives before the timeout, the packet is assumed lost and resent — which covers a packet that never arrived, since the receiver had nothing to checkthe timeout is the mark most often missed[1]

Acknowledgements handle corrupted packets; a timeout handles ones that never arrive.

1. Attenuation — the signal weakens over the distance until a bit is misread[1]
2. Interference from nearby electrical equipment, which a hospital has a great deal ofaccept skew if parallel[1]
3. A checksum on each packet, since it detects most corruption across the whole block rather than one byte at a timeaccept parity block with justification[1]
4. Patient data must be exactly correct — a single wrong digit in a dosage could cause harm — so a strong check is justified even at the cost of extra datathe justification must fit the context[1]
5. Detection only tells you the data is wrong; it does not deliver the correct data[1]
6. ARQ must be added so that any packet failing the check, or failing to arrive at all, is automatically requested again until it is received intact[1]

(a) attenuation and interference (b) a checksum, because the data must be exact (c) detection must be paired with ARQ so faulty packets are resent

It scrambles the data using a key so that it becomes meaningless to anyone who intercepts it. Only someone with the correct key can decrypt it back into readable form.

No. The data can still be intercepted, copied or deleted exactly as before. What encryption prevents is the interceptor understanding what they have taken, because without the key the ciphertext is unreadable.

Each extra bit doubles the number of possible keys, so a brute force attack — trying every key in turn — takes far longer. A key short enough to be tried exhaustively offers no real protection.

1. Symmetric uses the same key to encrypt and decrypt[1]
2. Advantage: it is much faster, so it suits large volumes of data[1]
3. Asymmetric uses a public key to encrypt and a matching private key to decrypt[1]
4. Advantage: no secret key needs to be exchanged, which removes the problem of getting the key to the recipient safelythe key distribution problem is the point[1]

Symmetric: one key, fast. Asymmetric: a public/private pair, no shared secret needed.

1. A public algorithm can be examined by cryptographers worldwide[1]
2. so weaknesses are found and corrected, rather than remaining hidden until an attacker discovers one[1]
3. Security rests entirely on the key, which remains secret — knowing the method does not read the message[1]
4. A secret algorithm has been checked by very few people, and once leaked offers no protection at all — "security through obscurity" is not security[1]

Public scrutiny finds weaknesses; secrecy rests on the key alone, not on the method.

1. The data is encrypted in the browser before it is sent, so anything intercepted on the way is ciphertext[1]
2. Only the shop's server holds the key needed to decrypt it, so an interceptor sees nothing usable[1]
3. Asymmetric encryption is used first, to exchange a symmetric key safely without any prior shared secret[1]
4. Then symmetric encryption is used for the actual data, because it is far faster for the volume involvedthe combination is the mark[1]
5. Encryption does not protect the data once it has been decrypted at the destination[1]
6. If the shop's database is later breached, or if the customer was tricked into sending details to a fake site in the first place, encryption offers no protection — it secured the journey, not the endpointsaccept phishing as the example[1]

(a) encrypted before sending, decryptable only by the server (b) asymmetric to exchange the key, symmetric for speed (c) it protects the journey, not the endpoints — a breached database or a fake site defeats it

A virus attaches itself to a host file and requires a user to run that file in order to spread. A worm is self-replicating and spreads across a network by itself, needing no user action at all.

An attacker tries every possible password in turn until one works. The most effective measure is to lock the account after a small number of failed attempts, which makes exhaustive guessing impossible however fast the attacker is.

It examines data entering or leaving a network and blocks anything not permitted by its rules, preventing unauthorised access and filtering out unwanted traffic.

1. Phishing sends a fraudulent message imitating a trusted organisation, containing a link to a fake site the victim must click[1]
2. Defence: check the sender and the true destination of any link, and never log in through a link — type the address yourself[1]
3. Pharming uses malicious code to alter DNS settings so that typing the correct address still leads to a fake siteno link is clicked[1]
4. Defence: anti-malware to prevent the DNS settings being altered, and checking the HTTPS certificate matches the site you intendedtyping the address does not help here[1]

Phishing needs a click; pharming redirects a correctly typed address. Different attacks, different defences.

1. Firewall — filters incoming and outgoing traffic, preventing unauthorised access from outside[1]
2. Anti-malware with automatic updates — detects and removes viruses, worms and spyware, and updates close known vulnerabilities[1]
3. Access levels — each user sees only what they need, so a compromised student account cannot reach staff records[1]
4. Two-factor authentication or strong password policy with lockout — protects against brute force and stolen passwordsaccept staff training against social engineering[1]

Firewall, anti-malware with updates, access levels, and strong authentication — each matched to its threat.

1. The website incident is a DDoS attack — the server is flooded with requests from many machines until it cannot respond to genuine users[1]
2. The password incident is social engineering — the attacker manipulated a person into revealing the password, with no technical attack at all[1]
3. A firewall filters network traffic against a set of rules[1]
4. The employee volunteered the password over the telephone, which never touched the network — no traffic rule could have detected itthe reason is the mark[1]
5. Against DDoS: traffic filtering at the firewall, rate limiting, or a service that absorbs and distributes the load[1]
6. Against social engineering: staff training and a strict procedure that credentials are never given out over the phone, with any such request verified by calling back on a known number[1]

(a) DDoS and social engineering (b) the password never crossed the network (c) traffic filtering, and training with a call-back verification policy