Networking - MCQ Practice Questions

Understanding:

We need to identify the network device that works at OSI Layer 2 and uses MAC addresses for frame forwarding decisions.

Step 1: Analyse each device by its OSI layer

A Hub operates at Layer 1 (Physical) and simply broadcasts all incoming signals to every port without any address-based decision making.

Step 2: Eliminate Layer 1 devices

Repeaters and Hubs work at Layer 1; they do not examine MAC or IP addresses.

Step 3: Identify Layer 2 vs Layer 3

Routers operate at Layer 3 (Network) and use IP addresses to make forwarding decisions. A Switch operates at Layer 2 (Data Link) and maintains a MAC address table (CAM table) to forward frames only to the port associated with the destination MAC address.

Answer:

A Switch is the device that operates at OSI Layer 2 and uses MAC addresses to intelligently forward frames to the correct port.

Quick Tip:

Remember the OSI layer mapping: Hub = Layer 1, Switch = Layer 2, Router = Layer 3. This is a very frequently tested concept in Indian competitive exams.

Understanding:

We need to find the device that connects two networks with different IP address ranges, meaning it must make decisions based on IP (Layer 3) information.

Step 1: Identify what connecting different IP networks requires

Connecting two networks with separate IP address ranges requires a device that can interpret IP addresses, determine the correct path between networks, and route packets accordingly.

Step 2: Evaluate each option

A Hub broadcasts data to all ports and operates at Layer 1 — it cannot distinguish between networks. A Switch uses MAC addresses at Layer 2 and can segment a single broadcast domain but cannot connect different IP networks. A Bridge operates at Layer 2 and connects similar network segments, not different IP networks. A Router operates at Layer 3 (Network layer), reads IP addresses, and routes packets between different logical networks.

Step 3: Confirm the correct choice

Only a Router has the capability to interconnect networks with different IP address schemes by using routing tables and IP-level forwarding.

Answer:

A Router is the correct device to connect two different IP network segments.

Quick Tip:

A key exam distinction: Switches connect devices within the same network (same subnet); Routers connect different networks (different subnets).

Understanding:

We need to identify the device where each port is its own collision domain, but all ports share a single broadcast domain.

Step 1: Define collision domain and broadcast domain

A collision domain is a network segment where simultaneous data transmissions can collide. A broadcast domain is the area within which a broadcast frame is forwarded.

Step 2: Analyse the Hub

A Hub places ALL ports in the same collision domain AND the same broadcast domain — it simply repeats signals to every port.

Step 3: Analyse the Switch

A Switch creates a separate collision domain per port because it buffers and forwards frames individually to each port. However, by default (without VLANs), all ports on a switch belong to the same broadcast domain, meaning a broadcast frame is sent to all ports.

Step 4: Analyse the Router

A Router creates both separate collision domains AND separate broadcast domains per interface — it does not forward broadcasts between interfaces.

Answer:

A Switch creates a separate collision domain per port while keeping all ports in the same broadcast domain by default.

Quick Tip:

To break up broadcast domains, you need either a Router or VLANs configured on a switch. This distinction is a classic exam trap.

Understanding:

We need to identify the primary function that distinguishes a gateway from other network devices.

Step 1: Eliminate clearly incorrect options

Amplifying and regenerating signals is the function of a Repeater. Assigning IP addresses dynamically is the role of a DHCP server. Filtering based on MAC addresses is the function of a Layer 2 Switch or Bridge.

Step 2: Define a Gateway

A Gateway is a network device that operates at multiple layers of the OSI model (up to Layer 7 in some implementations). Its primary and defining function is to connect two networks that may use entirely different communication protocols and perform the necessary protocol translation between them.

Step 3: Contextualise the role

For example, a gateway can connect a LAN using TCP/IP to a legacy network using a different protocol suite. In modern home networks, the term gateway often refers to a combined router and modem device, but the classical definition emphasises protocol translation.

Answer:

The primary function of a gateway is to connect networks using different communication protocols and translate between them.

Quick Tip:

A gateway is sometimes called a protocol converter. It is the most functionally complex of all basic network devices and can operate at all seven OSI layers if needed.

Understanding:

We need to identify which device stops broadcast frames from propagating beyond a network segment, thereby containing broadcast storms.

Step 1: Understand how each device handles broadcasts

A Hub forwards all signals, including broadcasts, to every connected port — it does not limit broadcasts at all.

Step 2: Evaluate Switch and Bridge

Both Switches and Bridges forward broadcast frames to all ports within their broadcast domain. They do not block broadcasts; they only separate collision domains. So they do not solve the broadcast propagation problem.

Step 3: Evaluate the Router

A Router, by design, does NOT forward broadcast frames between its interfaces. Each router interface defines a separate broadcast domain. Therefore, a broadcast originating on one side of a router will not cross to the other side.

Answer:

A Router is the most effective device to limit broadcast propagation, as it defines and separates broadcast domains.

Quick Tip:

This is a classic exam question. Remember: Switches separate collision domains; Routers separate broadcast domains. VLANs on a managed switch can also create separate broadcast domains without a physical router.

Understanding:

We need to identify the correct description of how a network bridge operates, including its OSI layer and addressing mechanism.

Step 1: Identify the OSI layer of a bridge

A Bridge operates at Layer 2 (Data Link layer) of the OSI model. It is not a Layer 1, Layer 3, or Layer 7 device.

Step 2: Understand the MAC-based filtering mechanism

A Bridge learns MAC addresses of devices on each of its segments by inspecting incoming frames. It builds a MAC address table and uses it to decide whether to forward a frame to the other segment or filter (drop) it if the destination is on the same segment as the source.

Step 3: Contrast with other devices

Option A describes a Router (Layer 3, IP addresses). Option B describes a Repeater (Layer 1, signal regeneration). Option D describes a Gateway (Layer 7, application protocol translation).

Answer:

A Bridge operates at OSI Layer 2 and uses MAC addresses to selectively filter and forward frames between two network segments.

Quick Tip:

A modern multi-port bridge is essentially what we call a Switch today. The bridge was the predecessor to the switch in network evolution.

Understanding:

We need to determine which wired network device a Wireless Access Point (WAP) most closely resembles in its fundamental operation.

Step 1: Understand what a WAP does

A WAP connects wireless devices to a wired network infrastructure. It operates at OSI Layer 2 (Data Link layer) and uses MAC addresses to manage communication between wireless clients and the wired network segment it is attached to.

Step 2: Compare to a Hub or Switch

A Hub (Layer 1) or Switch (Layer 2) connects multiple devices within the same network. A WAP performs an equivalent function for wireless devices — it acts as a central connection point for wireless clients, much like a switch or hub does for wired clients. Most modern WAPs function more like switches (forwarding based on MAC), but conceptually they serve the same aggregation/connection role.

Step 3: Eliminate other options

A Router connects different networks (Layer 3). A Firewall filters traffic based on security policies. A Repeater only regenerates signals. None of these match the core access-point role.

Answer:

A WAP is most similar to a Hub or Switch because it connects multiple end devices to a network at Layer 2 and provides network access, but does so wirelessly.

Quick Tip:

A home Wi-Fi router is actually a combination device: WAP + Switch + Router + often a DHCP server all in one box. Knowing this helps you answer combination-device questions.

Understanding:

We need to identify the primary benefit of configuring VLANs (Virtual Local Area Networks) on a managed switch.

Step 1: Define VLAN

A VLAN is a logical grouping of network devices configured on a switch, independent of their physical location. Devices in one VLAN cannot directly communicate with devices in another VLAN without a Layer 3 device (router or Layer 3 switch).

Step 2: Identify the primary benefit

By default, all ports on a switch are in the same broadcast domain. VLANs allow network administrators to divide a single physical switch into multiple logical segments, each acting as its own separate broadcast domain. This improves security, reduces unnecessary broadcast traffic, and simplifies network management.

Step 3: Eliminate incorrect options

VLANs do not affect physical cable speed. IP address assignment is the role of DHCP. VLANs do not eliminate the need for routing between different network segments — inter-VLAN communication still requires a router or Layer 3 switch.

Answer:

The primary benefit of VLANs is that a single physical switch can be logically divided into multiple separate broadcast domains.

Quick Tip:

For inter-VLAN routing (allowing devices in different VLANs to communicate), you need either a physical router using a router-on-a-stick configuration or a Layer 3 (multilayer) switch.

Understanding:

We need to identify the network device whose primary purpose is traffic inspection and enforcement of security rules to block or permit packets.

Step 1: Analyse each device

A Switch operates at Layer 2 and forwards frames based on MAC addresses — its purpose is efficient frame delivery, not security policy enforcement. A Repeater only regenerates signals at Layer 1. A Modem converts digital signals to analogue and vice versa for transmission over telephone or cable lines.

Step 2: Identify the Firewall

A Firewall is a dedicated network security device (or software) that monitors all incoming and outgoing network traffic. It evaluates each packet against a set of security rules (Access Control Lists, stateful inspection tables, or application-layer policies) and either permits or blocks the traffic accordingly.

Step 3: Confirm the role

Firewalls can operate at multiple OSI layers — packet-filtering firewalls work at Layer $\frac{3}{4}$, while next-generation firewalls (NGFWs) can inspect traffic up to Layer 7. Their defining characteristic is security policy enforcement.

Answer:

A Firewall is the device specifically designed to inspect network traffic and enforce security rules to allow or block packets.

Quick Tip:

Firewalls can be hardware-based (a dedicated appliance) or software-based (installed on a host). Stateful firewalls track connection state, making them more effective than simple stateless packet filters.

Understanding:

We need to identify the primary function of a Load Balancer in an enterprise network environment.

Step 1: Eliminate other network functions

Converting domain names to IP addresses is the function of a DNS server. Translating private IP addresses to a public IP address is the function of NAT (Network Address Translation), typically performed by a router or firewall. Caching web content to reduce bandwidth is the function of a Proxy Server or Web Cache.

Step 2: Define Load Balancer

A Load Balancer is a network device (hardware or software) that sits in front of a group of servers and intelligently distributes client requests across those servers. Its primary goals are to maximise throughput, minimise response time, avoid overloading any single server, and ensure high availability.

Step 3: Understand Load Balancing algorithms

Common algorithms used by load balancers include Round Robin, Least Connections, IP Hash, and Weighted Round Robin. The load balancer monitors server health and redirects traffic away from servers that are down or overloaded.

Answer:

A Load Balancer distributes incoming network traffic across multiple servers to prevent any single server from being overwhelmed and to ensure high availability.

Quick Tip:

Load Balancers are essential in data centres and cloud environments. They operate at Layer 4 (Transport — based on TCP/UDP) or Layer 7 (Application — based on HTTP content), and Layer 7 load balancers are more intelligent but computationally heavier.

Understanding:

We need to identify the IEEE standard number that corresponds to the Wi-Fi 6 generation of wireless networking.

Step 1: Map Wi-Fi generations to IEEE standards

The Wi-Fi Alliance assigns marketing names (Wi-Fi 4, 5, 6) to IEEE 802.11 amendments:

Step 2: Confirm key features of 802.11ax

802.11ax introduced OFDMA (Orthogonal Frequency Division Multiple Access), BSS Colouring, and Target Wake Time (TWT) to improve efficiency in dense environments. It operates on both 2.4 GHz and 5 GHz bands.

Answer:

The IEEE standard defining Wi-Fi 6 is IEEE 802.11ax.

Quick Tip:

Remember the progression: 802.11n (Wi-Fi 4) → 802.11ac (Wi-Fi 5) → 802.11ax (Wi-Fi 6). The 'x' in 802.11ax can be linked to 'six' as a memory aid.

Understanding:

We need to identify what the acronym SSID expands to in the context of wireless networking.

Step 1: Recall the definition

SSID stands for Service Set Identifier. It is the human-readable name assigned to a wireless network (Wi-Fi network). When a device scans for available Wi-Fi networks, the SSID is the name that appears in the list.

Step 2: Understand the context

A Basic Service Set (BSS) is a single access point with its clients. An Extended Service Set (ESS) is multiple BSSs sharing the same SSID to form a larger network. The SSID can be up to 32 characters in length and is broadcast in Beacon frames by the access point.

Answer:

SSID stands for Service Set Identifier.

Quick Tip:

Hiding the SSID (disabling SSID broadcast) provides only minimal security since the SSID is still transmitted in probe request/response frames and can be sniffed easily.

Understanding:

We need to identify the key establishment protocol introduced in WPA3-Personal that replaces the traditional PSK (Pre-Shared Key) method used in WPA2-Personal.

Step 1: Review WPA2-Personal limitations

WPA2-Personal uses a 4-way handshake based on a Pre-Shared Key. This is vulnerable to offline dictionary attacks — an attacker captures the handshake and brute-forces the password offline.

Step 2: Identify the WPA3-Personal improvement

WPA3-Personal replaces PSK with SAE (Simultaneous Authentication of Equals), which is based on the Dragonfly key exchange protocol. SAE provides forward secrecy, meaning even if the password is later compromised, previously captured traffic cannot be decrypted.

Step 3: Eliminate the other options

Answer:

WPA3-Personal uses SAE (Simultaneous Authentication of Equals) for key establishment.

Quick Tip:

SAE's resistance to offline dictionary attacks is the single most important security improvement WPA3 brings over WPA2 for home and small office networks.

Understanding:

We need to identify the multiple-access technology that Wi-Fi 6 (802.11ax) introduced to allow an AP to serve multiple clients simultaneously on sub-channels of a single channel.

Step 1: Distinguish OFDM from OFDMA

OFDM (used in 802.11a/g/n/ac) divides a channel into sub-carriers but assigns ALL sub-carriers to a SINGLE client at a time. OFDMA divides those same sub-carriers into Resource Units (RUs) and assigns different RUs to DIFFERENT clients simultaneously, dramatically improving efficiency in dense environments.

Step 2: Eliminate the other options

Step 3: Confirm OFDMA in 802.11ax

802.11ax uses OFDMA for both downlink (AP to clients) and uplink (clients to AP), which is a major efficiency gain over prior Wi-Fi generations.

Answer:

The technology is OFDMA (Orthogonal Frequency Division Multiple Access).

Quick Tip:

OFDMA is to OFDM what a multi-lane highway is to a single-lane road — multiple users move at the same time rather than waiting in sequence.

Understanding:

We need to determine how many non-overlapping channels exist in the 2.4 GHz Wi-Fi band given that channels are 22 MHz wide and spaced 5 MHz apart.

Formula:

To avoid overlap, two channels must be separated by at least:

Step 1: Identify the starting channels

Channels separated by at least 5 positions do not overlap. Starting from Channel 1:

Step 2: Check for a fourth non-overlapping channel

Channel 16 would start at 2481 MHz, but the 2.4 GHz band only extends to about 2483.5 MHz and Channel 14 (used only in Japan) ends at 2484 MHz. A full 22 MHz channel 16 would exceed the band, so no fourth non-overlapping channel fits in most regulatory domains.

Step 3: Conclusion

The three non-overlapping channels in the 2.4 GHz band (for most regions including India) are Channels 1, 6, and 11.

Answer:

There are 3 non-overlapping channels in the 2.4 GHz band.

Quick Tip:

Always deploy neighbouring access points on Channels 1, 6, and 11 in the 2.4 GHz band to prevent co-channel interference in dense deployments.

Understanding:

We need to understand the specific problem that the RTS/CTS handshake mechanism in 802.11 wireless networking is designed to solve.

Step 1: Define the hidden node problem

Two wireless clients A and C can both communicate with an access point B, but A and C cannot hear each other (they are 'hidden' from each other). If both transmit simultaneously, a collision occurs at B, but neither A nor C detects it — standard CSMA/CA fails here.

Step 2: Explain how RTS/CTS solves it

Step 3: Eliminate the other options

Answer:

RTS/CTS mitigates the hidden node problem by reserving the wireless medium before data transmission.

Quick Tip:

RTS/CTS adds overhead, so it is typically triggered only for large frames (above a configurable RTS threshold). For small frames, the overhead of RTS/CTS would outweigh the benefit.

Understanding:

We need to identify the wireless topology where devices communicate peer-to-peer without involving a central access point.

Step 1: Review wireless network modes

Step 2: Match definition to the question

The question describes direct client-to-client communication with no central AP, which precisely describes Ad hoc mode, standardized as IBSS in IEEE 802.11.

Answer:

The topology where wireless clients communicate directly without an access point is Ad hoc mode (IBSS).

Quick Tip:

Wi-Fi Direct (used in modern devices for file sharing) is a more modern peer-to-peer wireless standard that builds on ad hoc concepts but uses a soft-AP model, making it more scalable than classic IBSS.

Understanding:

We need to calculate the maximum theoretical PHY data rate for a single spatial stream in IEEE 802.11ac using:

Formula:

The PHY data rate is given by:

where $N_{\text{SD}}$ = number of data sub-carriers, $N_{\text{BPSC}}$ = bits per sub-carrier (log₂ of QAM order), $R_c$ = coding rate, $T_{\text{symbol}}$ = OFDM symbol duration.

Step 1: Identify parameters for 80 MHz channel

For an 80 MHz channel in 802.11ac:

Step 2: Substitute and calculate

Answer:

The maximum theoretical data rate for one spatial stream is 433.3 Mbps.

Quick Tip:

The 802.11ac maximum of 6.93 Gbps is achieved with 160 MHz channel width, 8 spatial streams, 256-QAM, and $\frac{5}{6}$ coding rate — each additional spatial stream multiplies the per-stream rate linearly.

Understanding:

We need to identify the specific role of Beacon frames that are periodically transmitted by an 802.11 access point.

Step 1: Define Beacon frames

Beacon frames are management frames sent by an access point at regular intervals (typically every 100 ms, known as the Target Beacon Transmission Time or TBTT). They serve as the primary advertisement mechanism for a wireless network.

Step 2: List what Beacon frames carry

A Beacon frame contains:

Step 3: Eliminate other options

Answer:

Beacon frames periodically announce the network's presence and provide synchronization information to clients.

Quick Tip:

Passive scanning relies on Beacon frames — a client listens on each channel waiting for a Beacon. Active scanning is faster — the client sends a Probe Request and the AP replies with a Probe Response containing the same information as a Beacon.

Understanding:

We need to identify the wireless security attack where an attacker creates a rogue access point mimicking a legitimate network's SSID to perform a man-in-the-middle interception.

Step 1: Define each option

Step 2: Match definition to question

The scenario precisely describes an evil twin attack — same SSID, rogue AP, traffic interception.

Answer:

The described attack is the Evil twin attack.

Quick Tip:

Connecting only to networks with WPA3 or verified certificates (in enterprise 802.1X environments) significantly reduces the risk of evil twin attacks, as the rogue AP cannot replicate the server certificate used in EAP authentication.