Networking - MCQ Practice Questions

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.