Protocols — Set 5

Correct Answer: A. SET

• **SET (Secure Electronic Transaction)** = a protocol jointly developed by Visa and Mastercard in 1996 to protect credit card transactions on the early internet — it used digital certificates and signatures to authenticate the cardholder, the merchant, and the bank independently, so the merchant never actually saw the card number. • **Key fact** — SET's triple-authentication design was its strength and its downfall; each party (buyer, seller, bank) needed a digital certificate installed and verified, making the system so complex that mass adoption never occurred. • SET was eventually superseded by the simpler SSL/TLS approach, where only the server is authenticated with a certificate and the encrypted channel protects the card number during transmission. • 💡 Option B (SSL) is wrong because SSL/TLS is a general encryption protocol for securing any data channel, not specifically designed for the cardholder-merchant-bank authentication model SET provided; Option C (HTTP) is wrong because plain HTTP has no encryption or security of any kind; Option D (TCP) is wrong because TCP is a transport protocol that handles data delivery, not payment security.

Correct Answer: B. IPMI

• **IPMI (Intelligent Platform Management Interface)** = a standardized hardware-level management interface embedded directly on a server's motherboard that allows administrators to monitor CPU temperature, fan speed, voltage, and power consumption — and even reboot or power-cycle the machine — without needing the operating system to be running. • **Key fact** — IPMI uses a dedicated microcontroller called the BMC (Baseboard Management Controller) that has its own network port and power supply, meaning a data center engineer can remotely manage a completely powered-off or crashed server from anywhere. • IPMI communicates over a separate management network (out-of-band) so that even a blue-screen or kernel panic does not cut off administrative access. • 💡 Option A (SNMP) is wrong because SNMP monitors network-attached devices through the OS and network stack — it stops working when the OS crashes; Option C (HTTP) is wrong because HTTP is the web protocol for browsing, not for hardware-level server management; Option D (FTP) is wrong because FTP transfers files and has no ability to read hardware sensors or control server power states.

Correct Answer: C. UDP

• **UDP (User Datagram Protocol)** = a connectionless, lightweight transport protocol that sends data packets (datagrams) to a destination without establishing a connection first or verifying that they arrived — the sender simply fires packets and moves on. • **Key fact** — because UDP has no handshake, no acknowledgement, and no retransmission, its header is only 8 bytes compared to TCP's 20+ bytes, making it significantly faster for applications where a dropped packet is preferable to a delayed one (live video, DNS lookups, online games). • UDP is the protocol of choice for real-time streaming because a retransmitted video frame arriving late is worse than simply skipping it. • 💡 Option A (TCP) is wrong because TCP is connection-oriented and guarantees delivery with retransmissions, making it too slow for time-sensitive communication; Option B (HTTP) is wrong because HTTP is an application-layer web protocol that runs on top of TCP, not a transport protocol itself; Option D (SSH) is wrong because SSH is an application-layer remote access protocol, not a transport-layer protocol at all.

Correct Answer: C. Routing Protocol

• **Routing Protocol** = the category of protocol (including OSPF, RIP, BGP, EIGRP) that routers use to advertise which IP networks they can reach, so that every router in the network can dynamically build and update its forwarding table without human intervention. • **Key fact** — routing protocols are divided into Interior Gateway Protocols (IGPs like OSPF and RIP that operate within one organization's network) and Exterior Gateway Protocols (EGPs like BGP that operate between different organizations or ISPs). • Without routing protocols, an administrator would need to manually enter a static route on every router for every possible destination, which would be completely unmanageable on the global internet. • 💡 Option A (IP) is wrong because IP is the packet-delivery protocol that uses routing tables to forward packets, but it does not build or distribute those tables itself; Option B (TCP) is wrong because TCP handles reliable data transport between two endpoints and has no role in distributing routing information; Option D (DNS) is wrong because DNS translates domain names to IP addresses and plays no part in telling routers how to forward packets.

Correct Answer: A. NTP

• **NTP (Network Time Protocol)** = a protocol that synchronizes the clocks of all computers on a network to a common reference time, typically accurate to within a few milliseconds, using a hierarchical tree of time servers called strata. • **Key fact** — Stratum 0 sources are atomic clocks or GPS receivers; Stratum 1 servers connect directly to them; Stratum 2 servers sync from Stratum 1, and so on — the number tells you how many hops away from an authoritative clock a server is. • Accurate time is not just a convenience — SSL certificates, authentication systems like Kerberos, and database transaction logs all depend on synchronized clocks; a clock drift of even a few minutes can cause authentication failures. • 💡 Option B (DNS) is wrong because DNS resolves domain names to IP addresses and has nothing to do with time synchronization; Option C (HTTP) is wrong because HTTP transfers web page data between browsers and servers, not time data; Option D (FTP) is wrong because FTP is a file transfer protocol with no mechanism for clock synchronization.

Correct Answer: B. MQTT

• **MQTT (Message Queuing Telemetry Transport)** = a lightweight publish-subscribe protocol where IoT devices (publishers) send sensor data to a central broker, and cloud servers or apps (subscribers) receive only the topics they have registered interest in — all over a tiny, persistent TCP connection. • **Key fact** — MQTT's entire protocol overhead can be as small as 2 bytes per message, making it ideal for battery-powered sensors on low-bandwidth cellular or satellite links where every byte of data costs money or power. • The broker in the middle (e.g., Eclipse Mosquitto or AWS IoT Core) decouples publishers from subscribers, so a temperature sensor does not need to know who is consuming its data. • 💡 Option A (HTTP) is wrong because HTTP's request-response overhead and stateless nature make it too heavy for constrained IoT devices that need constant lightweight communication; Option C (FTP) is wrong because FTP is designed for bulk file transfer between computers, not for tiny real-time sensor readings; Option D (TELNET) is wrong because Telnet is an insecure remote terminal access protocol with no publish-subscribe capability.

Correct Answer: C. RARP

• **RARP (Reverse Address Resolution Protocol)** = an early protocol that worked in the opposite direction of ARP — a device that knew only its own MAC address (burned into hardware at manufacture) would broadcast a RARP request, and a RARP server on the network would look up the matching IP address in a manually maintained table and reply. • **Key fact** — RARP was primarily used by diskless workstations that had no storage to remember their own IP between reboots; it was later replaced by BOOTP and then DHCP, which added options like subnet mask and gateway along with the IP address. • RARP operated at the Data Link layer, making it non-routable — a separate RARP server was needed on every network segment, which was a major operational drawback. • 💡 Option A (ARP) is wrong because ARP maps a known IP address to an unknown MAC address — the reverse direction; Option B (DNS) is wrong because DNS translates domain names to IP addresses, not MAC addresses to IP addresses; Option D (DHCP) is wrong because DHCP is RARP's modern successor that dynamically assigns IPs from a pool rather than from a static lookup table.

Correct Answer: A. SSL/TLS

• **SSL/TLS (Transport Layer Security)** = the cryptographic protocol responsible for the HTTPS handshake — after the TCP connection is open, TLS negotiates which cipher suite to use, exchanges digital certificates to verify the server's identity, and derives shared encryption keys, all before a single byte of web content moves. • **Key fact** — in TLS 1.3 (the current standard), the handshake completes in just one round trip (1-RTT), cutting the latency of older TLS versions in half; this means the secure channel is established almost instantly. • The padlock icon in your browser's address bar is a direct visual confirmation that a TLS handshake succeeded and all subsequent data is encrypted. • 💡 Option B (TCP) is wrong because TCP's three-way handshake only establishes the transport connection — it provides no encryption or identity verification; Option C (IP) is wrong because IP handles packet routing across networks and has no concept of session security; Option D (UDP) is wrong because UDP is a connectionless protocol that performs no handshake at all.

Correct Answer: B. DHCP

• **DHCP (Dynamic Host Configuration Protocol)** = a server-based protocol that automatically assigns a unique IP address from a managed pool (scope) to each device that joins the network, preventing conflicts and eliminating the need for manual configuration. • **Key fact** — DHCP uses a four-step DORA process (Discover → Offer → Request → Acknowledge): the client broadcasts a Discover, the server replies with an Offer of an available IP, the client Requests that specific IP, and the server sends an Acknowledgement to confirm the lease. • DHCP leases are temporary — the server assigns an IP for a limited time (e.g., 24 hours), and the client must renew it before expiry, allowing the server to reclaim addresses from devices that have left the network. • 💡 Option A (DNS) is wrong because DNS translates domain names to IP addresses — it does not assign IP addresses to client devices; Option C (ARP) is wrong because ARP resolves an IP address to a MAC address on the local network segment, not distribute IP addresses; Option D (SMTP) is wrong because SMTP is the email transmission protocol with no role in network address management.

Correct Answer: B. HTTPS

• **HTTPS (HyperText Transfer Protocol Secure)** = the encrypted version of HTTP where all web content — including passwords, form data, and cookies — is transmitted inside a TLS tunnel, making it unreadable to anyone who intercepts the traffic. • **Key fact** — HTTPS uses port 443 by default, whereas plain HTTP uses port 80; browsers enforce HTTPS through HSTS (HTTP Strict Transport Security) headers that instruct the browser to never connect to that site over plain HTTP again. • Google's search ranking algorithm gives preference to HTTPS sites, which has driven nearly universal adoption — today over 95% of web traffic is encrypted. • 💡 Option A (HTTP) is wrong because plain HTTP sends all data including login credentials in clear text that anyone on the same network can read; Option C (FTP) is wrong because FTP is designed for file transfer, not for serving web pages securely; Option D (SSH) is wrong because SSH is a command-line remote access protocol — while it is encrypted, it is not used to transfer web pages to browsers.