Question 1

At the data link layer, which mechanism is primarily used to detect transmission errors in frames before they are accepted by the receiver?

Accepted Answer

Introduction / Context: The data link layer packages network-layer packets into frames and is responsible for detecting corrupted frames so they can be discarded or retransmitted. A widely used technique for error detection at this layer is the cyclic redundancy check (CRC). Given Data / Assumptions: We are focusing on error detection (not correction) at the data link layer. Typical link technologies (Ethernet, 802.11, many serial links) attach a CRC to each frame. The receiver recomputes and compares the CRC to detect corruption. Concept / Approach: CRC treats the bit string as coefficients of a polynomial over GF(2). The transmitter divides by a generator polynomial and appends the remainder (the CRC). The receiver repeats the division; a nonzero remainder indicates an error. Step-by-Step Solution: 1) Choose a generator polynomial G(x) standardized for the link (e.g., CRC-32 for Ethernet).2) Compute remainder R = Data(x) * x^k mod G(x), where k is CRC length.3) Append R to the frame as the FCS (frame check sequence).4) Receiver divides (Data || R) by G(x).5) If remainder = 0, accept; else, discard or request retransmission. Verification / Alternative check: CRCs detect common error patterns (single-bit errors, burst errors up to a length bound) with extremely low undetected error probability when G(x) is well-chosen. Why Other Options Are Wrong: Bit stuffing: A framing method to avoid flag emulation in bit-oriented protocols; not error detection. Hamming codes: Primarily for error correction; used at physical/other layers, not typically the default link-layer detector. Equalization: Channel compensation at the physical layer, not link-layer detection. Scrambling: Randomizes patterns to aid timing/EMI; not an integrity check. Common Pitfalls: Confusing CRC (detection) with FEC (correction). Also thinking a CRC fixes errors; it only detects them. Final Answer: cyclic redundancy codes

Question 2

What is the standard term for transmitting computerized data from one location to another over a communication channel?

Accepted Answer

Introduction / Context: When computers exchange information over any medium (wired or wireless), we use specific terminology to describe the act and the systems involved. The umbrella term for sending and receiving data between endpoints is data communication. Given Data / Assumptions: We are naming the activity of moving data across distance. Endpoints may be computers, servers, or network devices. Any physical medium (copper, fiber, radio) may be used. Concept / Approach: Data communication encompasses the processes, protocols, and hardware that enable the reliable exchange of bits. It includes encoding, synchronization, addressing, error detection, and flow control, depending on the layer under discussion. Step-by-Step Solution: 1) Identify the activity: sending data from source to destination.2) Recognize that this involves communication functions across layers (physical to application).3) The established term for this activity is “data communication.” Verification / Alternative check: Standard textbooks and curricula label the overall process and field as “data communications and networking.” Why Other Options Are Wrong: Data transfer: Colloquial for moving files/bytes, but the field/act is more formally “data communication.” Data flow: Describes directionality/throughput, not the general activity name. Data management: Concerns storage, organization, governance, not transmission. Information warehousing: Focuses on analytical storage systems, not transmission. Common Pitfalls: Using narrow terms (e.g., “file transfer”) to describe the entire communication stack. Final Answer: data communication

Question 3

Which of the following is an example of an analog communication method or medium capable of carrying analog signals?

Accepted Answer

Introduction / Context: Analog communication conveys information using continuously varying signals such as amplitude, frequency, or phase. Many physical media and carriers can support analog modulation schemes, including light and radio-frequency paths as well as wired lines. Given Data / Assumptions: We are identifying media/methods that can carry analog signals. Examples include optical, RF/microwave, and legacy telephony wiring. Question asks whether each given example qualifies. Concept / Approach: In practice, a “method” or “medium” is analog-capable if it can transport a waveform whose amplitude/phase/frequency vary continuously. Many channels can carry either analog or digitally modulated signals; capability for analog is the key. Step-by-Step Solution: 1) Laser beam: Light intensity or phase can be analog-modulated (e.g., AM, FM, PM of an optical carrier).2) Microwave: RF carriers are classically used with analog FM/AM/PM; microwave links historically carried analog TV and voice.3) Voice grade telephone line: Designed originally for analog voice (300–3400 Hz) and supports analog modems.4) Therefore, all listed items are valid analog-capable communication methods/media. Verification / Alternative check: Historical deployments (analog TV over microwave, analog telephony, optical analog links) confirm analog carriage on all three media. Why Other Options Are Wrong: None of the above: Incorrect because each listed medium can carry analog signals. Common Pitfalls: Assuming lasers and microwaves are “digital only.” The modulation format (analog vs digital) is a choice; the medium often supports both. Final Answer: All of the above

Question 4

In electronic mail systems, what do we call the component that connects two or more dissimilar email systems and transfers messages among them?

Accepted Answer

Introduction / Context: Early and even modern email infrastructures often involve different systems and protocols (e.g., SMTP, X.400, proprietary groupware). A special component is needed to interconnect these heterogeneous worlds and relay messages between them. Given Data / Assumptions: We need a function that interlinks different mail systems. It must accept messages in one format and deliver them in another when necessary. It performs routing/translation between domains or protocols. Concept / Approach: A mail gateway is designed for inter-system mail exchange and format translation. It differs from user-facing software (user agents) and link-layer devices (bridges) that operate at different layers/concerns. Step-by-Step Solution: 1) Identify the need: interconnect heterogeneous email systems.2) Recognize the specialized role: accept, translate (if needed), and forward messages.3) The correct term is “mail gateway.” Verification / Alternative check: Standard email architectures show gateways between SMTP-based systems and other mail domains or legacy protocols. Why Other Options Are Wrong: Gateways (generic): Too broad; the precise term here is mail gateway. Bridges: Operate at data-link level to forward frames; not an email-layer function. User Agent: Client software (e.g., Outlook) for composing/reading mail, not inter-system transport. Message spooler: Queueing component, not necessarily cross-system translator. Common Pitfalls: Confusing a general network gateway with the specific mail gateway function, or mixing up user agents and transport relays. Final Answer: mail gateway

Question 5

In computer-based decision support, when the system presents a list of predefined choices for the manager to select from, which prompting technique is being used?

Accepted Answer

Introduction / Context: Decision support and transaction systems often guide users through interfaces that constrain inputs to improve speed, accuracy, and consistency. Offering a set list of options reduces ambiguity and data-entry errors. Given Data / Assumptions: The computer provides a multiple-choice list. The manager selects one item from that list. This interaction aims to streamline decision entry. Concept / Approach: Presenting predefined choices is characteristic of menu-driven interfaces. The user navigates and selects from available commands or values, as opposed to typing free text or answering open-ended prompts. Step-by-Step Solution: 1) Identify that choices are predefined and enumerable.2) Recognize the UI pattern: menu selection.3) Conclude that the prompting technique is “menu selection.” Verification / Alternative check: UI design textbooks classify such interactions explicitly as menu selection, distinct from dialog boxes requiring typed responses. Why Other Options Are Wrong: Question and answer: Typically involves typed responses to specific prompts. Form filling: Structured fields, not necessarily multiple-choice menus. Open-ended question: Invites free-form responses, not predefined choices. Free-form text entry: No predefined options, opposite of menu selection. Common Pitfalls: Equating any guided input with forms; menus are specifically about picking from a list. Final Answer: menu selection

Question 6

Your R&D team is comparing baseband and broadband networking. Which statement correctly contrasts baseband and broadband on a single cable?

Accepted Answer

Introduction / Context: Baseband and broadband describe how signals share a medium. Understanding the difference guides technology selection for LANs, MANs, and access networks. Given Data / Assumptions: We compare how many channels share one physical cable. We assume traditional definitions used in networking texts. Physical details like modulation are abstracted. Concept / Approach: Baseband transmits a single digital signal over the entire bandwidth of the medium (one channel per cable). Broadband uses frequency-division techniques to carry multiple independent channels simultaneously on the same cable. Step-by-Step Solution: 1) Baseband: entire medium bandwidth devoted to one channel; signaling is typically digital.2) Broadband: divide medium bandwidth into sub-bands; modulate carriers so several channels coexist.3) Therefore, the correct contrast is: baseband = single channel per cable; broadband = several channels per cable. Verification / Alternative check: Historical examples: Ethernet on coax (baseband) vs CATV coax (broadband) carrying TV channels and data simultaneously. Why Other Options Are Wrong: Several cables carry one channel: Impractical and not the definition of baseband. LAN vs WAN distinction: Scope (LAN/WAN) is not inherent to baseband/broadband. Fixed vs variable bit rates: Not the defining property. Infrared-only: Incorrect; terms apply across many media and frequencies. Common Pitfalls: Assuming “broadband” simply means “fast.” It specifically implies multiple channels via frequency division. Final Answer: Baseband networks carry a single channel on a single cable, whereas broadband networks carry several channels on a single cable

Question 7

An 8 Mbps token ring uses a token holding timer of 10 ms. Ignoring header bits, what is the maximum frame size that a station can transmit during one token hold?

Accepted Answer

Introduction / Context: In token ring networks, a station may transmit only while it holds the token, bounded by a token holding timer. The maximum frame length is limited by link rate and token hold time. Given Data / Assumptions: Bit rate = 8 Mbps (8 x 10^6 bits per second). Token holding time = 10 ms (0.01 s). Header/overhead negligible for this calculation. Concept / Approach: Maximum bits sendable = data_rate * time_window. Convert bits to bytes by dividing by 8 to get frame size in bytes. Step-by-Step Solution: 1) Compute bits in 10 ms: bits = 8 x 10^6 * 0.01 = 80,000 bits.2) Convert to bytes: 80,000 / 8 = 10,000 bytes.3) Therefore, the longest frame size is 10,000 B (ignoring headers). Verification / Alternative check: Cross-check units: Mbps is bits/s; multiplying by seconds yields bits; dividing by 8 yields bytes. No other constraints given, so 10,000 B stands. Why Other Options Are Wrong: 8000 B: Corresponds to 64,000 bits, which would require only 8 ms at 8 Mbps; underestimates the maximum. 80,000 B: Equals 640,000 bits, exceeding what can be sent in 10 ms at 8 Mbps. 8 x 10^5 bit frame: 800,000 bits; also too large. 1000 B: Only 8,000 bits; far below the limit. Common Pitfalls: Confusing Mbps (bits) with MBps (bytes) and forgetting to divide by 8; mixing milliseconds and seconds. Final Answer: 10,000 B frame

Question 8

Compared to analog signals, digital signals typically allow faster transmission rates and provide higher accuracy/robustness under noise. Which choice captures this comparison?

Accepted Answer

Introduction / Context: A core advantage of digital communication is that it represents information with discrete symbols (bits). This supports high-rate multiplexing and robust regeneration, improving practical throughput and reliability compared to many analog systems under similar conditions. Given Data / Assumptions: We compare digital and analog signaling in typical modern networks. Noise and distortion are present in real channels. Coding, regeneration, and error control are available in digital systems. Concept / Approach: Digital links support precise thresholding and regeneration at repeaters, enabling long chains without cumulative noise. Advanced modulation/coding packs more bits per hertz, often yielding higher effective data rates than legacy analog systems, while keeping error rates low. Step-by-Step Solution: 1) Faster transmission: Digital modulation, compression, and multiplexing (e.g., QAM, OFDM, TDM) enable high bit rates per channel.2) More accurate: Binary decision thresholds plus error detection/correction reduce the impact of moderate noise.3) Therefore, both attributes usually apply to digital signals compared to analog for data networking. Verification / Alternative check: Practical systems (Ethernet, fiber links, cellular data) achieve gigabit+ rates with low bit error rates, outperforming analog data carriage. Why Other Options Are Wrong: Only faster or only more accurate: Incomplete; both are typical advantages. All of the above: Includes statements not listed; incorrect distractor. Neither: Contradicts widespread empirical evidence. Common Pitfalls: Assuming “accuracy” means perfect; digital still suffers errors but can keep them acceptably low with coding and proper SNR. Final Answer: both (a) and (b)

Question 9

In computer networks, the act of sending a file from your personal computer’s primary memory or disk to a remote computer or server over a communication link is called.

Accepted Answer

Introduction: In basic computer networking and Internet usage, it is common to move data between a local machine and a remote system. Understanding the correct term for sending a file outward from your device is essential for accurate communication and troubleshooting. Given Data / Assumptions: You have a personal computer with a file stored on disk or in memory. A remote system (server or another computer) is reachable over a network. A communication protocol such as HTTP, HTTPS, FTP, SFTP, or SCP is used. Concept / Approach: When data flows from the local machine to a remote system, the operation is termed “upload.” When the direction is remote to local, the operation is “download.” These terms are direction-centric and independent of protocol choice; the role of client and server does not change the naming of the direction of data transfer from the user’s perspective. Step-by-Step Solution: 1) Identify direction of transfer: local PC → remote system.2) Map direction to standard term: local to remote = upload.3) Validate with common tools: web forms (file inputs) and cloud drives refer to this as “Upload.”4) Confirm that downloading is the opposite direction: remote → local. Verification / Alternative check: In FTP or SFTP clients, actions are labeled “Upload” for sending files to the server and “Download” for retrieving them. Likewise, cloud storage buttons are typically “Upload” for local → cloud. Why Other Options Are Wrong: Downloading: opposite direction (remote to local). Logging on: refers to authentication/session start, not file transfer. Handshaking: initial protocol negotiation (e.g., TCP setup), not a data copy action. Synchronizing: two-way state alignment; not the specific one-way action described. Common Pitfalls: Users often confuse upload with download because both may occur during a session. Remember the viewpoint: from your device outward is upload; from the Internet inward is download. Final Answer: Uploading

Question 10

In data communications, modulation is the process of altering a carrier wave so that it conveys digital information by representing bits as analog signal variations for transmission over analog media.

Accepted Answer

Introduction: Modulation is a foundational concept in data and telecommunication systems that enables computers and other digital devices to send information across channels originally designed for analog signals (e.g., radio, telephone lines). Given Data / Assumptions: A digital bitstream must traverse an analog physical medium. A sinusoidal carrier (characterized by amplitude, frequency, and phase) is available. Receiver and transmitter share a compatible modulation/demodulation scheme. Concept / Approach: Modulation maps digital bits to changes in a carrier wave: amplitude (ASK), frequency (FSK), or phase (PSK). This process effectively converts digital signals to analog signals suitable for the channel. At the receiving end, demodulation reverses the process to recover the original bitstream. Step-by-Step Solution: 1) Start with digital data (bits).2) Choose a modulation scheme (e.g., BPSK, QPSK, QAM).3) Vary carrier parameters according to bit patterns to produce an analog waveform.4) Transmit the modulated analog signal; receiver demodulates to reconstruct bits. Verification / Alternative check: Observe that analog phone lines and RF channels require analog waveforms. Practical systems (DSL, Wi-Fi, cellular) all modulate carriers to embed digital information. Why Other Options Are Wrong: Converting analog to digital: that is sampling/quantization/ADC, not modulation. Multiplexing: combines multiple signals but does not impose data onto a carrier. Encryption: secures data but does not change physical signal form. Error-correcting coding: adds redundancy; still distinct from the carrier alteration process. Common Pitfalls: Confusing modulation with encoding or multiplexing. Modulation changes the carrier; encoding changes bit patterns; multiplexing shares bandwidth among flows. Final Answer: Converting digital signals to analog signals

Question 11

In IP networking, identify the standard loopback address used to test the local TCP/IP stack on the host itself.

Accepted Answer

Introduction: The loopback mechanism lets a system send packets to itself to validate the local TCP/IP stack, sockets, and software without using any physical network interface. Given Data / Assumptions: Loopback uses the special Class A block 127.0.0.0/8. Typical diagnostic tools include ping and local servers bound to 127.0.0.1. Concept / Approach: Any address in 127.0.0.0/8 refers to the local host, with 127.0.0.1 traditionally used as the canonical loopback address. Packets never leave the host; they are internally short-circuited by the IP stack. Step-by-Step Solution: 1) Recognize that 127/8 is reserved for loopback.2) Identify the conventional single-address form: 127.0.0.1.3) Confirm by using “ping 127.0.0.1” to test local IP. Verification / Alternative check: Binding a service to 127.0.0.1 restricts access to the local machine only; external clients cannot connect, confirming the loopback semantics. Why Other Options Are Wrong: 0.0.0.1: not loopback; 0.0.0.0/8 has special meanings (this host, default routes). 127.0.0.0: network address of the loopback block, not the standard host address. 255.255.255.255: limited broadcast. 169.254.0.1: APIPA/LLA for link-local addressing, not loopback. Common Pitfalls: Confusing 127.0.0.1 with localhost DNS name mappings or assuming any private RFC1918 address is loopback (they are not). Final Answer: 127.0.0.1

Question 12

In data communications, the term “residual error rate” refers to which probability when an error detection scheme is employed?

Accepted Answer

Introduction: Reliability metrics quantify how often communication systems deliver incorrect bits. “Residual error rate” specifically addresses the fraction of errors that slip past an error-detection mechanism such as parity, checksum, or CRC. Given Data / Assumptions: An error detection scheme (e.g., CRC) is in use. Noise on the channel can flip bits or corrupt frames. Detection is very good but not perfect. Concept / Approach: Error detection codes map valid data to codewords; some error patterns may map one valid codeword into another undetectably. The residual error rate is the probability that a corrupted frame passes the detector as if it were correct, i.e., an undetected error reaches higher layers. Step-by-Step Solution: 1) Channel introduces bit errors with some raw bit error rate (BER).2) Detector flags most corrupted frames; those are dropped/retransmitted.3) A small subset of corruptions mimic valid codewords and escape detection.4) The frequency of such escapes defines the residual error rate. Verification / Alternative check: CRC polynomials are selected to minimize undetected patterns (e.g., detect all single-bit errors, most burst errors up to length L). Despite this, the residual is nonzero but extremely small for strong CRCs. Why Other Options Are Wrong: Bit errors per 24 hours: a time-based count, not a probability of undetected errors. Probability of detection: that measures success at catching errors, not misses. SNR divided by Eb/N0: unrelated physical-layer ratio. Perfect correction probability: not a standard metric and not about undetected errors. Common Pitfalls: Confusing BER, FER (frame error rate), and residual error rate. Residual error rate is conditional on the presence of an error detection mechanism and focuses on undetected errors that pass through as valid. Final Answer: Probability that one or more errors remain undetected when error detection is used

Question 13

You have a Class B address block starting with 150.x.x.x and need at least 16 subnets (6 existing sites + 10 planned). Which subnet mask maximizes hosts per subnet while meeting this requirement?

Accepted Answer

Introduction: Subnetting trades host capacity for additional network segments. For a Class B network (e.g., 150.x.x.x), choosing the right mask depends on the required number of subnets and the desire to maximize hosts per subnet. Given Data / Assumptions: Base class: Class B (default mask 255.255.0.0, i.e., /16). Required subnets: at least 16 (6 current + 10 planned). Objective: meet subnet count with the fewest borrowed bits to keep more host addresses per subnet. Concept / Approach: In Class B, subnetting borrows bits from the third octet first. To get ≥16 subnets, borrow 4 bits (since 2^4 = 16). A /16 becomes /20. The corresponding third-octet value is 240, yielding the dotted mask 255.255.240.0, maximizing hosts while meeting exactly 16 subnets. Step-by-Step Solution: 1) Start with /16 (255.255.0.0).2) Need 16 subnets → borrow 4 bits: /16 + 4 = /20.3) Third-octet mask with 4 high bits set is 240.4) Final mask: 255.255.240.0 → correct choice corresponds to “240.” Verification / Alternative check: Hosts per /20 subnet = 2^(32-20) - 2 = 4094, which is ample for most sites and larger than alternatives that borrow more bits. Why Other Options Are Wrong: 192 (255.255.192.0): borrows only 2 bits → 4 subnets (insufficient). 224 (255.255.224.0): borrows 3 bits → 8 subnets (still insufficient). 248 (255.255.248.0): 5 bits → 32 subnets (extra but fewer hosts per subnet than necessary). 252 (255.255.252.0): 6 bits → 64 subnets (even smaller host pools). Common Pitfalls: Forgetting the goal to maximize host counts leads to borrowing more bits than needed. Always match the minimum required subnet count to minimize host loss. Final Answer: 240

Question 14

In the OSI model, which layer’s protocols directly support end users and application programs with services such as authentication, resource sharing, file transfer, and network management?

Accepted Answer

Introduction: The OSI model separates networking functions into layers. Understanding which layer provides user-facing application services clarifies protocol roles and troubleshooting responsibilities. Given Data / Assumptions: OSI layers from top to bottom: 7 Application, 6 Presentation, 5 Session, 4 Transport, 3 Network, 2 Data Link, 1 Physical. Services in question: authentication, resource sharing, file transfer, network management. Concept / Approach: Layer 7 (Application) interfaces with user applications, offering protocols such as HTTP, FTP, SMTP, SNMP, and more. While lower layers enable delivery, Layer 7 defines how applications access network services and data formats expected by those applications. Step-by-Step Solution: 1) Map services (file transfer, management) to known protocols (FTP, TFTP, SNMP).2) Recognize these operate at the Application layer.3) Confirm that Presentation (L6) focuses on translation/encryption and Session (L5) on dialog control—not user-facing applications. Verification / Alternative check: Practical stacks (TCP/IP) collapse OSI layers, but application protocols still conceptually sit at the top layer that interacts with software the user runs. Why Other Options Are Wrong: Layer 6: data representation (encryption/format conversion). Layer 5: session establishment/teardown. Layer 4: end-to-end transport (TCP/UDP). Layer 3: routing and logical addressing (IP). Common Pitfalls: Assuming encryption always means Application layer; many encryption functions map to Presentation or to Transport (e.g., TLS) depending on model interpretation. Final Answer: Layer 7 protocols

Question 15

For connecting a computer to another device located in the same room (short distance, point-to-point), which physical medium would you most likely choose?

Accepted Answer

Introduction: Short-reach device interconnection within a single room typically favors simple, low-cost, and low-latency cabling solutions. The choice should match distance, bandwidth, and practicality. Given Data / Assumptions: Devices are co-located in the same room. Direct, point-to-point connectivity is sufficient. Cost and complexity should be minimal. Concept / Approach: For very short distances, direct cabling (e.g., coaxial, twisted pair, or short USB/HDMI) is common. Among the provided options, coaxial cable represents a straightforward local wiring method, unlike wide-area or specialized carrier solutions. Step-by-Step Solution: 1) Determine scope: intra-room connectivity.2) Prefer simple physical media with adequate shielding and bandwidth.3) From listed choices, coaxial cable fits the practical requirement. Verification / Alternative check: Ethernet over short copper or even a short coax segment is a widely-used, inexpensive approach compared with carrier-based or satellite links. Why Other Options Are Wrong: Dedicated leased line: a telecom-provided WAN circuit, unnecessary and expensive for same-room links. Satellite ground station: designed for long-distance RF connectivity, not local patching. All of the above: incorrect because not all listed items are appropriate. Microwave backhaul: used for building-to-building or long-haul links, not inside a room. Common Pitfalls: Assuming “bigger” technologies are better. For local connections, simpler is almost always better—short copper or coax runs solve the problem efficiently. Final Answer: a coaxial cable

Question 16

Which sequence correctly shows the default subnet masks for Class A, Class B, and Class C IPv4 networks?

Accepted Answer

Introduction: Legacy classful IPv4 addressing assigns default masks based on address class. Although modern networks use CIDR, knowing the defaults remains useful for exams and interpreting historical configurations. Given Data / Assumptions: Class A ranges start 0–127, default mask /8 → 255.0.0.0. Class B ranges start 128–191, default mask /16 → 255.255.0.0. Class C ranges start 192–223, default mask /24 → 255.255.255.0. Concept / Approach: Match each class to its default prefix length and derive the dotted-decimal mask. The correct order A, B, C corresponds to /8, /16, /24 respectively. Step-by-Step Solution: 1) Class A → /8 → 255.0.0.0.2) Class B → /16 → 255.255.0.0.3) Class C → /24 → 255.255.255.0. Verification / Alternative check: CIDR generalizes these, but routers and textbooks still reference these defaults for historical context and subnetting examples. Why Other Options Are Wrong: Option B: lists the masks in reverse order (C, B, A). Option D: includes 255.255.255.255 which is a host route/broadcast context, not a class default mask. Option A/E: invalid or unrelated sequences. Common Pitfalls: Confusing class defaults with commonly deployed subnetted CIDR masks; the question asks specifically for the default classful masks. Final Answer: 255.0.0.0, 255.255.0.0, 255.255.255.0

Question 17

In host name resolution, what is the maximum length constraint commonly applied to a single HOSTS file entry (i.e., a fully qualified domain name)?

Accepted Answer

Introduction: HOSTS files map IP addresses to host names locally. Understanding name length constraints helps avoid invalid entries that resolvers may ignore or mishandle. Given Data / Assumptions: Domain naming follows DNS conventions even in HOSTS files. A fully qualified domain name (FQDN) length limits typically apply. Concept / Approach: DNS rules set a maximum FQDN length of 255 characters (including dots). Individual labels between dots are typically limited to 63 characters. While OS parsing may vary, these canonical limits are widely observed in tools and libraries used by operating systems. Step-by-Step Solution: 1) Consider that HOSTS entries mirror DNS names.2) Apply DNS FQDN limit: up to 255 characters.3) Ensure each label is ≤63 characters to maintain compatibility. Verification / Alternative check: RFC-aligned resolvers and libraries commonly enforce these constraints. Empirically, overly long names fail resolution or are truncated, which effectively enforces the 255-character boundary. Why Other Options Are Wrong: 8: far too small; legacy 8.3 limitations are DOS file names, not host names. 500/Unlimited: exceed DNS limits and would break interoperability. 63: this is the per-label limit, not the total FQDN length for the entire entry. Common Pitfalls: Confusing per-label and total-length constraints. Ensure both are met: total ≤255, each label ≤63, and allowed characters only (letters, digits, hyphen) with labels not starting/ending with a hyphen. Final Answer: 255

Question 18

You manage three contiguous /24 networks 192.168.5.0, 192.168.6.0, and 192.168.7.0. Which single subnet mask can supernet them into one route?

Accepted Answer

Introduction: Route aggregation (supernetting) reduces routing table entries by combining contiguous networks into a larger block with a shorter prefix (larger host portion). Given Data / Assumptions: Three /24 networks: 192.168.5.0, .6.0, .7.0. They are numerically contiguous. Goal: one summarized route covering all three. Concept / Approach: A /22 prefix (255.255.252.0) covers a block size of 4 in the third octet, aligning on multiples of 4 (…0, 4, 8, …). The smallest /22 that includes .5, .6, and .7 must begin at .4 and spans .4–.7, thereby covering 5–7. Step-by-Step Solution: 1) Determine block size needed: 3 contiguous /24s require at least a /22 (four /24s).2) Find boundary: nearest /22 boundary at 192.168.4.0.3) /22 covers 192.168.4.0–192.168.7.255, which includes 5.0, 6.0, 7.0.4) Dotted mask for /22 is 255.255.252.0 → correct. Verification / Alternative check: Count networks: a /22 aggregates 4 class C (/24) networks; our set of three fits within the .4–.7 window, ensuring full coverage without holes. Why Other Options Are Wrong: 225.255.254.0: invalid mask (225 in an octet is not a legal mask value). 255.255.255.240 / 255.255.255.252: far too small; these are /28 and /30 masks. 255.255.254.0: /23 covers only two contiguous /24s; insufficient for three. Common Pitfalls: Forgetting that supernets must align on natural boundaries (multiples of block size). Misalignment can cause the summary not to include all target networks. Final Answer: 255.255.252.0

Question 19

In computer networking support, the first step in troubleshooting many user-reported problems is to verify the client’s basic TCP/IP stack status and configuration before checking servers or advanced settings. What should you confirm first on the af…

Accepted Answer

Introduction / Context: In day-to-day desktop and helpdesk networking, many incidents stem from local misconfiguration rather than core network outages. A systematic approach starts at the endpoint's TCP/IP stack—the foundation required for any IP-based communication. Given Data / Assumptions: Client is unable to access network resources. Environment uses standard IPv4 with common Windows/Linux tools. No prior confirmation exists about local TCP/IP health. Concept / Approach: Always begin troubleshooting from the lowest practical layer: the client's network stack and link status. Confirm that the TCP/IP stack is present, enabled, and bound to the active adapter. Without a working stack, further tests (DNS, routing, servers) will fail. Step-by-Step Solution: 1) Check adapter status: link up, correct driver, not disabled.2) Verify TCP/IP is installed/bound to the adapter and not uninstalled or corrupted.3) Inspect IP settings (IP address, subnet mask, gateway, DNS).4) Test local stack with loopback (ping 127.0.0.1) and self IP.5) Proceed outward (default gateway, DNS, application servers) only after the stack is good. Verification / Alternative check: Use ipconfig/ifconfig to confirm configuration and ping/arp to validate local resolution. If loopback fails, the stack is broken regardless of network conditions. Why Other Options Are Wrong: Subnet mask validity matters but comes after confirming the stack exists.WINS server status is irrelevant in most modern environments and not a first check.BDC operability (legacy domain controller) is not the first local validation step.“None of the above” is incorrect because verifying TCP/IP installation is the correct first check. Common Pitfalls: Jumping to DNS or server-side issues before validating the client, ignoring disabled adapters, and skipping loopback tests. Final Answer: TCP/IP is installed correctly on the client.

Question 20

In data communications, buffering refers to temporarily storing data so that devices with slightly different speeds can communicate smoothly without loss or jitter. Which statement best describes buffering?

Accepted Answer

Introduction / Context: Buffering is a core concept in operating systems and networks that helps smooth out timing differences between producers and consumers of data, avoiding underflow or overflow in pipelines. Given Data / Assumptions: Two endpoints operate at slightly different rates. Intermediate memory (buffers) is available. Lossless delivery is desired. Concept / Approach: A buffer is temporary memory that holds data so that a faster sender does not overwhelm a slower receiver. It decouples rates and absorbs jitter. This is used in NIC queues, OS socket buffers, disk I/O, streaming media, and routers. Step-by-Step Solution: 1) Sender writes to a buffer at its rate.2) Receiver reads from the buffer at its own rate.3) As long as average rates match and buffer capacity suffices, no data is lost.4) Flow control may throttle the sender if the buffer approaches capacity. Verification / Alternative check: Observe queue lengths or playback stability; steady buffers indicate effective smoothing of rate variance. Why Other Options Are Wrong: Reducing cross-talks is an analog physical-layer concern, not buffering.Routing overhead is a control-plane issue; buffering does not inherently reduce route computations.“Storage within the transmitting medium” describes store-and-forward switching generically, not the purpose of buffering.“None of the above” is wrong because option A is correct. Common Pitfalls: Confusing buffering with caching (temporal locality optimization) or with error correction; mixing up flow control and congestion control. Final Answer: Buffering is temporary storage that absorbs speed variations.

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