Telecommunications and Wireless
Communications Comprehensive WGU D413
– Exam (Questions 1-50) Questions with
Correct DETAILED ANSWERs and
Explanations.
Domain: OSI Model, TCP/IP, and Network Fundamentals
1. At which layer of the OSI model does a network switch primarily operate when
making forwarding decisions based on MAC addresses?
• A) Layer 1 - Physical
• B) Layer 2 - Data Link
• C) Layer 3 - Network
• D) Layer 4 - Transport
Correct DETAILED ANSWER: B) Layer 2 - Data Link
Explanation: A standard Ethernet switch operates at Layer 2, the Data Link layer. It
learns MAC addresses from incoming frames, builds a MAC address table (CAM table),
and forwards frames out the specific port where the destination MAC address resides.
This is transparent bridging/switching. Layer 3 switches exist and can route based on IP
addresses, but the fundamental switching function is Layer 2.
,2. Which protocol is responsible for resolving an IP address to a MAC address on
an Ethernet network?
• A) DNS (Domain Name System)
• B) DHCP (Dynamic Host Configuration Protocol)
• C) ARP (Address Resolution Protocol)
• D) ICMP (Internet Control Message Protocol)
Correct DETAILED ANSWER: C) ARP (Address Resolution Protocol)
Explanation: ARP operates between Layer 2 and Layer 3. When a device knows the
destination IP address but not the corresponding MAC address, it broadcasts an ARP
request ("Who has 192.168.1.1? Tell 192.168.1.100"). The device with that IP responds
with a unicast ARP reply containing its MAC address. This mapping is cached in the ARP
table to avoid repeated lookups.
3. A technician needs to transfer a file between two servers where speed is critical
and occasional packet loss is acceptable. Which transport layer protocol should be
selected?
• A) TCP (Transmission Control Protocol)
• B) UDP (User Datagram Protocol)
• C) ICMP (Internet Control Message Protocol)
• D) ARP (Address Resolution Protocol)
Correct DETAILED ANSWER: B) UDP (User Datagram Protocol)
Explanation: UDP is connectionless and provides no guarantee of delivery, ordering, or
error recovery. This makes it lightweight and fast with minimal overhead. It is ideal for
applications where speed trumps reliability, such as streaming media, VoIP, online
gaming, and TFTP file transfers. TCP, with its three-way handshake, acknowledgments,
and retransmissions, would add overhead and latency.
4. What is the primary function of the Presentation layer (Layer 6) in the OSI
model?
, • A) Routing packets between different networks.
• B) Establishing, managing, and terminating sessions between applications.
• C) Translating, encrypting, and compressing data for the application layer.
• D) Providing reliable end-to-end data delivery.
Correct DETAILED ANSWER: C) Translating, encrypting, and compressing data for
the application layer.
Explanation: The Presentation layer acts as a translator for the network. It ensures data
from one system's Application layer is readable by another. Key functions include: data
format translation (e.g., ASCII to EBCDIC), character encoding (Unicode), data
encryption/decryption (TLS/SSL operates here conceptually), and data compression
(JPEG, MPEG).
5. In the TCP three-way handshake, what is the correct sequence of flags for
establishing a connection?
• A) SYN, ACK, FIN
• B) SYN, SYN-ACK, ACK
• C) SYN, RST, ACK
• D) ACK, SYN-ACK, SYN
Correct DETAILED ANSWER: B) SYN, SYN-ACK, ACK
Explanation: The client initiates: (1) Client sends a TCP segment with the SYN flag set
and a random sequence number. (2) Server responds with a segment with both SYN and
ACK flags set, acknowledging the client's sequence number and providing its own. (3)
Client sends a final ACK segment acknowledging the server's sequence number. The
connection is now established.
Domain: IP Addressing and Subnetting
Communications Comprehensive WGU D413
– Exam (Questions 1-50) Questions with
Correct DETAILED ANSWERs and
Explanations.
Domain: OSI Model, TCP/IP, and Network Fundamentals
1. At which layer of the OSI model does a network switch primarily operate when
making forwarding decisions based on MAC addresses?
• A) Layer 1 - Physical
• B) Layer 2 - Data Link
• C) Layer 3 - Network
• D) Layer 4 - Transport
Correct DETAILED ANSWER: B) Layer 2 - Data Link
Explanation: A standard Ethernet switch operates at Layer 2, the Data Link layer. It
learns MAC addresses from incoming frames, builds a MAC address table (CAM table),
and forwards frames out the specific port where the destination MAC address resides.
This is transparent bridging/switching. Layer 3 switches exist and can route based on IP
addresses, but the fundamental switching function is Layer 2.
,2. Which protocol is responsible for resolving an IP address to a MAC address on
an Ethernet network?
• A) DNS (Domain Name System)
• B) DHCP (Dynamic Host Configuration Protocol)
• C) ARP (Address Resolution Protocol)
• D) ICMP (Internet Control Message Protocol)
Correct DETAILED ANSWER: C) ARP (Address Resolution Protocol)
Explanation: ARP operates between Layer 2 and Layer 3. When a device knows the
destination IP address but not the corresponding MAC address, it broadcasts an ARP
request ("Who has 192.168.1.1? Tell 192.168.1.100"). The device with that IP responds
with a unicast ARP reply containing its MAC address. This mapping is cached in the ARP
table to avoid repeated lookups.
3. A technician needs to transfer a file between two servers where speed is critical
and occasional packet loss is acceptable. Which transport layer protocol should be
selected?
• A) TCP (Transmission Control Protocol)
• B) UDP (User Datagram Protocol)
• C) ICMP (Internet Control Message Protocol)
• D) ARP (Address Resolution Protocol)
Correct DETAILED ANSWER: B) UDP (User Datagram Protocol)
Explanation: UDP is connectionless and provides no guarantee of delivery, ordering, or
error recovery. This makes it lightweight and fast with minimal overhead. It is ideal for
applications where speed trumps reliability, such as streaming media, VoIP, online
gaming, and TFTP file transfers. TCP, with its three-way handshake, acknowledgments,
and retransmissions, would add overhead and latency.
4. What is the primary function of the Presentation layer (Layer 6) in the OSI
model?
, • A) Routing packets between different networks.
• B) Establishing, managing, and terminating sessions between applications.
• C) Translating, encrypting, and compressing data for the application layer.
• D) Providing reliable end-to-end data delivery.
Correct DETAILED ANSWER: C) Translating, encrypting, and compressing data for
the application layer.
Explanation: The Presentation layer acts as a translator for the network. It ensures data
from one system's Application layer is readable by another. Key functions include: data
format translation (e.g., ASCII to EBCDIC), character encoding (Unicode), data
encryption/decryption (TLS/SSL operates here conceptually), and data compression
(JPEG, MPEG).
5. In the TCP three-way handshake, what is the correct sequence of flags for
establishing a connection?
• A) SYN, ACK, FIN
• B) SYN, SYN-ACK, ACK
• C) SYN, RST, ACK
• D) ACK, SYN-ACK, SYN
Correct DETAILED ANSWER: B) SYN, SYN-ACK, ACK
Explanation: The client initiates: (1) Client sends a TCP segment with the SYN flag set
and a random sequence number. (2) Server responds with a segment with both SYN and
ACK flags set, acknowledging the client's sequence number and providing its own. (3)
Client sends a final ACK segment acknowledging the server's sequence number. The
connection is now established.
Domain: IP Addressing and Subnetting
