Networking Concepts practice questions

A device is configured with IP address 192.168.1.130 and subnet mask 255.255.255.192. What is the network address of this device?

Trap 1: 192.168.1.0

This would be the network address if the subnet were /24, but with /26 it is not correct.

Trap 2: 192.168.1.192

This network address covers 192-255, which does not include 130.

Trap 3: 192.168.1.64

This network address covers 64-127, which does not include 130.

A
192.168.1.0
Why it fails: This would be the network address if the subnet were /24, but with /26 it is not correct.
B
192.168.1.128
Correct: 130 is in the range 128-191, so the network address is 192.168.1.128.
C
192.168.1.192
Why it fails: This network address covers 192-255, which does not include 130.
D
192.168.1.64
Why it fails: This network address covers 64-127, which does not include 130.

Question 2easymultiple choice

A network engineer is designing a subnet that can support at least 10 hosts. Which subnet mask would provide exactly 14 usable host addresses?

Trap 1: /27

A /27 subnet mask provides 5 host bits (32-27), resulting in 2^5 = 32 total addresses. After accounting for the network and broadcast addresses, this yields 30 usable host addresses. While 30 hosts certainly meets the 'at least 10' requirement, it allocates significantly more addresses than necessary, leading to inefficient use of the IP address space and potential for address exhaustion in larger network designs.

Trap 2: /29

A /29 subnet mask allocates only 3 bits for host addresses (32-29). This results in 2^3 = 8 total IP addresses. Subtracting the mandatory network address and broadcast address leaves only 6 usable host addresses, which is insufficient to meet the requirement of at least 10 hosts for the subnet.

Trap 3: /30

A /30 subnet mask reserves 2 bits for host addresses (32-30), which generates 2^2 = 4 total IP addresses. When the network and broadcast addresses are excluded, only 2 usable host addresses remain. This is far below the minimum requirement of 10 hosts and is typically reserved for point-to-point links between two devices, not for supporting multiple endpoints within a local area network.

A
/27
Why it fails: A /27 subnet mask provides 5 host bits (32-27), resulting in 2^5 = 32 total addresses. After accounting for the network and broadcast addresses, this yields 30 usable host addresses. While 30 hosts certainly meets the 'at least 10' requirement, it allocates significantly more addresses than necessary, leading to inefficient use of the IP address space and potential for address exhaustion in larger network designs.
B
/28
A /28 CIDR prefix designates 4 host bits (32-28), yielding 2^4 = 16 total IP addresses within the subnet. After reserving the network address and broadcast address, this leaves 14 usable host addresses. This perfectly satisfies the requirement of supporting at least 10 hosts, making it the most efficient choice without excessive waste of IP address space.
C
/29
Why it fails: A /29 subnet mask allocates only 3 bits for host addresses (32-29). This results in 2^3 = 8 total IP addresses. Subtracting the mandatory network address and broadcast address leaves only 6 usable host addresses, which is insufficient to meet the requirement of at least 10 hosts for the subnet.
D
/30
Why it fails: A /30 subnet mask reserves 2 bits for host addresses (32-30), which generates 2^2 = 4 total IP addresses. When the network and broadcast addresses are excluded, only 2 usable host addresses remain. This is far below the minimum requirement of 10 hosts and is typically reserved for point-to-point links between two devices, not for supporting multiple endpoints within a local area network.

Question 3easymultiple choice

A network engineer needs to transfer a large database file from one server to another across a WAN link. The transfer must be reliable and guarantee that the data arrives without errors. Which transport layer protocol should the engineer use?

Trap 1: UDP

UDP (User Datagram Protocol) is a connectionless transport protocol that offers no guarantees of delivery, ordering, or error checking. While it provides speed due to its minimal overhead, it lacks the retransmission and flow control mechanisms essential for ensuring that all parts of a large database file arrive intact and in the correct sequence. Using UDP for such a transfer would risk significant data loss and corruption.

Trap 2: IP

IP (Internet Protocol) operates at the Network layer, handling the logical addressing and routing of packets between different networks. Its primary function is to deliver individual packets from a source host to a destination host, but it offers no end-to-end reliability, ordering, or error recovery for the data within those packets. IP relies on higher-layer protocols, like TCP, to provide such transport-layer guarantees for application data.

Trap 3: ICMP

ICMP (Internet Control Message Protocol) operates at the Network layer and is primarily designed for sending error messages and operational information, such as network reachability (ping) or route tracing (traceroute). It does not provide mechanisms for application-level data transfer, nor does it offer any reliability features like retransmission or flow control necessary for moving large files.

A
UDP
Why it fails: UDP (User Datagram Protocol) is a connectionless transport protocol that offers no guarantees of delivery, ordering, or error checking. While it provides speed due to its minimal overhead, it lacks the retransmission and flow control mechanisms essential for ensuring that all parts of a large database file arrive intact and in the correct sequence. Using UDP for such a transfer would risk significant data loss and corruption.
B
IP
Why it fails: IP (Internet Protocol) operates at the Network layer, handling the logical addressing and routing of packets between different networks. Its primary function is to deliver individual packets from a source host to a destination host, but it offers no end-to-end reliability, ordering, or error recovery for the data within those packets. IP relies on higher-layer protocols, like TCP, to provide such transport-layer guarantees for application data.
C
TCP
TCP (Transmission Control Protocol) is a connection-oriented protocol that ensures reliable, ordered, and error-checked delivery of data. For transferring a large database file, TCP establishes a connection, segments the data, and reassembles it at the destination, retransmitting any lost or corrupted segments. This guarantees data integrity and completeness, which is paramount for critical file transfers like databases.
D
ICMP
Why it fails: ICMP (Internet Control Message Protocol) operates at the Network layer and is primarily designed for sending error messages and operational information, such as network reachability (ping) or route tracing (traceroute). It does not provide mechanisms for application-level data transfer, nor does it offer any reliability features like retransmission or flow control necessary for moving large files.

Question 4mediummultiple choice

A network engineer needs to assign IP addresses to a new subnet that will support exactly 25 devices. Which subnet mask would provide the minimum number of usable host addresses while still accommodating the requirement?

Trap 1: 255.255.255.240 (/28)

/28 provides 14 usable hosts, which is insufficient for 25 devices.

Trap 2: 255.255.255.192 (/26)

/26 provides 62 usable hosts, which is more than needed but not the minimum.

Trap 3: 255.255.255.128 (/25)

/25 provides 126 usable hosts, far exceeding the need and not the minimal subnet.

A
255.255.255.240 (/28)
Why it fails: /28 provides 14 usable hosts, which is insufficient for 25 devices.
B
255.255.255.224 (/27)
/27 provides 28 usable hosts, which meets the requirement with minimal waste.
C
255.255.255.192 (/26)
Why it fails: /26 provides 62 usable hosts, which is more than needed but not the minimum.
D
255.255.255.128 (/25)
Why it fails: /25 provides 126 usable hosts, far exceeding the need and not the minimal subnet.

Question 5mediummultiple choice

A company needs a subnet that will support exactly 50 devices. Which subnet mask provides the minimum number of usable host addresses while still accommodating the requirement?

Trap 1: 255.255.255.128 (/25)

A /25 subnet mask allocates 25 bits to the network portion, leaving 7 bits available for host addresses. This provides 2^7 = 128 total IP addresses within the subnet. After accounting for the network and broadcast addresses, 126 usable host addresses are available. While this subnet can accommodate 50 devices, it provides significantly more addresses than needed, leading to inefficient IP address utilization and potential waste of valuable address space.

Trap 2: 255.255.255.224 (/27)

A /27 subnet mask designates 27 bits for the network, leaving only 5 bits for host addresses. This results in 2^5 = 32 total IP addresses for the subnet. Subtracting the network and broadcast addresses leaves only 30 usable host addresses, which is insufficient to support the required 50 devices. Therefore, this subnet is too small for the company's needs.

Trap 3: 255.255.255.240 (/28)

A /28 subnet mask reserves 28 bits for the network, leaving only 4 bits for host addresses. This configuration provides 2^4 = 16 total IP addresses for the subnet. After deducting the network and broadcast addresses, only 14 usable host addresses remain. This is far too few to support the company's requirement for 50 devices, making it an entirely inadequate choice.

A
255.255.255.128 (/25)
Why it fails: A /25 subnet mask allocates 25 bits to the network portion, leaving 7 bits available for host addresses. This provides 2^7 = 128 total IP addresses within the subnet. After accounting for the network and broadcast addresses, 126 usable host addresses are available. While this subnet can accommodate 50 devices, it provides significantly more addresses than needed, leading to inefficient IP address utilization and potential waste of valuable address space.
B
255.255.255.192 (/26)
A /26 subnet mask utilizes 26 bits for the network portion, leaving 6 bits for host addresses. This configuration yields 2^6 = 64 total IP addresses within the subnet. After reserving the network address and broadcast address, 62 usable host addresses remain, which is the smallest subnet that can precisely accommodate the requirement of 50 devices without excessive waste.
C
255.255.255.224 (/27)
Why it fails: A /27 subnet mask designates 27 bits for the network, leaving only 5 bits for host addresses. This results in 2^5 = 32 total IP addresses for the subnet. Subtracting the network and broadcast addresses leaves only 30 usable host addresses, which is insufficient to support the required 50 devices. Therefore, this subnet is too small for the company's needs.
D
255.255.255.240 (/28)
Why it fails: A /28 subnet mask reserves 28 bits for the network, leaving only 4 bits for host addresses. This configuration provides 2^4 = 16 total IP addresses for the subnet. After deducting the network and broadcast addresses, only 14 usable host addresses remain. This is far too few to support the company's requirement for 50 devices, making it an entirely inadequate choice.

Question 6easymultiple choice

A technician needs to connect two different networks and forward traffic based on IP addresses. Which of the following devices operates at Layer 3 of the OSI model and should be used?

Trap 1: Hub

A hub operates at Layer 1 of the OSI model, functioning as a basic multi-port repeater for electrical signals. When a signal arrives on one port, the hub simply regenerates and broadcasts it out to all other connected ports without any intelligent processing or forwarding decisions. Consequently, hubs create a single large collision domain and cannot differentiate traffic based on IP addresses or any other network-layer information.

Trap 2: Switch

A switch operates at Layer 2 (Data Link Layer) of the OSI model, forwarding data frames based on the destination MAC address. Unlike a router, a switch primarily connects devices within the same local area network (LAN) or broadcast domain, learning MAC addresses and building a MAC address table to direct traffic efficiently. It does not inspect or make forwarding decisions based on Layer 3 IP addresses, making it unsuitable for routing traffic between different IP networks.

Trap 3: Bridge

A bridge is a Layer 2 device that connects two or more network segments, typically within the same broadcast domain, by forwarding frames based on MAC addresses. Its primary function is to segment a single large collision domain into smaller ones, improving network performance by filtering traffic between segments. However, like a switch, a bridge operates solely at the data link layer and lacks the intelligence to interpret IP addresses or route traffic between distinct IP networks.

A
Hub
Why it fails: A hub operates at Layer 1 of the OSI model, functioning as a basic multi-port repeater for electrical signals. When a signal arrives on one port, the hub simply regenerates and broadcasts it out to all other connected ports without any intelligent processing or forwarding decisions. Consequently, hubs create a single large collision domain and cannot differentiate traffic based on IP addresses or any other network-layer information.
B
Switch
Why it fails: A switch operates at Layer 2 (Data Link Layer) of the OSI model, forwarding data frames based on the destination MAC address. Unlike a router, a switch primarily connects devices within the same local area network (LAN) or broadcast domain, learning MAC addresses and building a MAC address table to direct traffic efficiently. It does not inspect or make forwarding decisions based on Layer 3 IP addresses, making it unsuitable for routing traffic between different IP networks.
C
Router
Routers are essential Layer 3 network devices specifically designed to connect disparate networks and intelligently forward data packets between them. They achieve this by examining the destination IP address within each packet and consulting their internal routing tables to determine the optimal path. This capability allows them to facilitate communication across different subnets and even the internet, making them fundamental for inter-network connectivity.
D
Bridge
Why it fails: A bridge is a Layer 2 device that connects two or more network segments, typically within the same broadcast domain, by forwarding frames based on MAC addresses. Its primary function is to segment a single large collision domain into smaller ones, improving network performance by filtering traffic between segments. However, like a switch, a bridge operates solely at the data link layer and lacks the intelligence to interpret IP addresses or route traffic between distinct IP networks.

Question 7easymultiple choice

A network administrator needs to create a subnet that supports exactly 50 hosts. Which subnet mask provides the smallest subnet that meets this requirement?

Trap 1: A

A /25 subnet mask dedicates 25 bits to the network, providing 7 bits for host addresses. This results in 2^7 = 128 total IP addresses, which translates to 126 usable host addresses after accounting for the network and broadcast identifiers. While 126 addresses are more than enough for 50 hosts, this option is not the most efficient use of IP space. The question implies selecting the smallest subnet that meets the exact requirement, which /25 exceeds significantly.

Trap 2: C

A /27 subnet mask designates 27 bits for the network, leaving 5 bits for host addresses. This configuration yields 2^5 = 32 total IP addresses. Subtracting the network and broadcast addresses leaves only 30 usable host addresses. This quantity is insufficient to support the required 50 hosts, falling short by 20 addresses.

Trap 3: D

A /28 subnet mask utilizes 28 bits for the network portion, leaving only 4 bits for host addresses. This configuration provides 2^4 = 16 total IP addresses. After subtracting the network and broadcast addresses, only 14 usable host addresses remain. This number is substantially less than the 50 hosts required, rendering this subnet completely inadequate.

A
A
Why it fails: A /25 subnet mask dedicates 25 bits to the network, providing 7 bits for host addresses. This results in 2^7 = 128 total IP addresses, which translates to 126 usable host addresses after accounting for the network and broadcast identifiers. While 126 addresses are more than enough for 50 hosts, this option is not the most efficient use of IP space. The question implies selecting the smallest subnet that meets the exact requirement, which /25 exceeds significantly.
B
B
A /26 subnet mask allocates 26 bits for the network portion, leaving 6 bits for host addresses. This configuration provides 2^6 = 64 total IP addresses. After reserving two addresses for the network identifier and broadcast address, 62 usable host addresses remain. This is the smallest subnet size that can accommodate exactly 50 hosts, making it the most efficient choice.
C
C
Why it fails: A /27 subnet mask designates 27 bits for the network, leaving 5 bits for host addresses. This configuration yields 2^5 = 32 total IP addresses. Subtracting the network and broadcast addresses leaves only 30 usable host addresses. This quantity is insufficient to support the required 50 hosts, falling short by 20 addresses.
D
D
Why it fails: A /28 subnet mask utilizes 28 bits for the network portion, leaving only 4 bits for host addresses. This configuration provides 2^4 = 16 total IP addresses. After subtracting the network and broadcast addresses, only 14 usable host addresses remain. This number is substantially less than the 50 hosts required, rendering this subnet completely inadequate.

Review the full OSPF breakdown →

Question 8hardmultiple choice

A network engineer configures OSPF on two routers with a primary link (1 Gbps) and a backup link (100 Mbps). The engineer expects traffic to always use the primary link unless it fails, but the router is sending traffic over the backup link. What is the most likely cause?

Trap 1: The backup link has a lower OSPF cost than the primary link.

While it is true that OSPF will always prefer a path with a lower cost, stating that 'the backup link has a lower OSPF cost than the primary link' describes the outcome rather than the root cause from the primary link's perspective. The issue arises because the *intended primary* link's cost is comparatively higher, leading OSPF to select the backup path. This option merely reiterates the observed behavior without pinpointing the specific configuration error on the primary link that led to this preference.

Trap 2: The reference bandwidth is set to 1 Gbps on the primary router.

OSPF calculates interface cost using the formula 'reference bandwidth divided by interface bandwidth'. The default reference bandwidth is 100 Mbps. If the reference bandwidth on the primary router were set to 1 Gbps (1000 Mbps), a 1 Gbps primary link would have a cost of 1 (1000/1000). A typical 100 Mbps backup link would then have a cost of 10 (1000/100). This configuration would cause the primary link to be preferred due to its lower cost, which directly contradicts the problem statement where traffic is flowing over the backup link.

Trap 3: The bandwidth command is misconfigured on the backup interface.

The `bandwidth` command on an interface directly influences its OSPF cost, as OSPF uses this value in its cost calculation. While a misconfiguration on the backup interface could certainly alter its OSPF cost, the central problem described is the *primary* link not being preferred. If the backup interface's bandwidth were misconfigured in a way that made its OSPF cost lower than the primary, it would contribute to the issue. However, the most direct cause for the primary link being ignored is a higher OSPF cost configured on the primary link itself, making it less attractive than the backup.

A
The backup link has a lower OSPF cost than the primary link.
Why it fails: While it is true that OSPF will always prefer a path with a lower cost, stating that 'the backup link has a lower OSPF cost than the primary link' describes the outcome rather than the root cause from the primary link's perspective. The issue arises because the *intended primary* link's cost is comparatively higher, leading OSPF to select the backup path. This option merely reiterates the observed behavior without pinpointing the specific configuration error on the primary link that led to this preference.
B
The OSPF cost of the primary link is higher than the backup link.
OSPF utilizes cost as its primary metric for path selection, always favoring routes with the lowest cumulative cost to a destination. If the network engineer intends a specific link to be primary, its OSPF cost must be explicitly configured to be lower than any intended backup paths. In this scenario, if the designated primary link possesses a higher OSPF cost than the backup link, OSPF will logically install the backup link into the routing table as the preferred path, diverting traffic away from the intended primary.
C
The reference bandwidth is set to 1 Gbps on the primary router.
Why it fails: OSPF calculates interface cost using the formula 'reference bandwidth divided by interface bandwidth'. The default reference bandwidth is 100 Mbps. If the reference bandwidth on the primary router were set to 1 Gbps (1000 Mbps), a 1 Gbps primary link would have a cost of 1 (1000/1000). A typical 100 Mbps backup link would then have a cost of 10 (1000/100). This configuration would cause the primary link to be preferred due to its lower cost, which directly contradicts the problem statement where traffic is flowing over the backup link.
D
The bandwidth command is misconfigured on the backup interface.
Why it fails: The `bandwidth` command on an interface directly influences its OSPF cost, as OSPF uses this value in its cost calculation. While a misconfiguration on the backup interface could certainly alter its OSPF cost, the central problem described is the *primary* link not being preferred. If the backup interface's bandwidth were misconfigured in a way that made its OSPF cost lower than the primary, it would contribute to the issue. However, the most direct cause for the primary link being ignored is a higher OSPF cost configured on the primary link itself, making it less attractive than the backup.

Question 9hardmultiple choice

A network engineer is troubleshooting connectivity issues between two data center switches that are configured to support jumbo frames with an MTU of 9000. The link is a 10 Gigabit Ethernet fiber connection. Large file transfers fail, but small transfers succeed. What is the most likely cause?

Trap 1: A

10 Gigabit Ethernet is widely supported and not the cause of this specific issue.

Trap 2: B

While a faulty fiber cable could cause general failures, the pattern of small transfers working and large transfers failing points to an MTU issue.

Trap 3: D

TCP window size affects throughput but not the ability to transfer large files at all; small transfers would also fail if window size were severely misconfigured.

A
A
Why it fails: 10 Gigabit Ethernet is widely supported and not the cause of this specific issue.
B
B
Why it fails: While a faulty fiber cable could cause general failures, the pattern of small transfers working and large transfers failing points to an MTU issue.
C
C
An intermediate device with a standard MTU will drop large frames, causing jumbo frame traffic to fail.
D
D
Why it fails: TCP window size affects throughput but not the ability to transfer large files at all; small transfers would also fail if window size were severely misconfigured.

Question 10easymultiple choice

Which of the following devices operates at Layer 3 of the OSI model and makes forwarding decisions based on destination IP addresses?

Trap 1: Switch

A network switch primarily operates at Layer 2 (Data Link Layer) of the OSI model. Its core function is to forward data frames within a single local area network (LAN) segment by learning and using Media Access Control (MAC) addresses. When a frame arrives, the switch consults its MAC address table to determine the correct outgoing port, thereby reducing unnecessary traffic and improving network efficiency compared to hubs. It does not inspect or route based on Layer 3 IP addresses.

Trap 2: Bridge

A network bridge is a Layer 2 (Data Link Layer) device designed to connect two separate network segments, effectively creating a single, larger collision domain. Like a switch, it learns MAC addresses of devices on each segment and forwards frames selectively based on the destination MAC address. Bridges are typically simpler than switches, often having fewer ports, but they perform the same fundamental function of segmenting traffic at the MAC address level, not at the IP layer.

Trap 3: Hub

A network hub operates at Layer 1 (Physical Layer) of the OSI model, functioning as a multi-port repeater. When a signal arrives at one port, the hub simply regenerates it and broadcasts it out to all other connected ports, regardless of the intended recipient. This lack of intelligence means all devices connected to a hub share a single collision domain, leading to inefficient network traffic and potential performance bottlenecks, as it does not perform any MAC or IP address-based forwarding.

A
Switch
Why it fails: A network switch primarily operates at Layer 2 (Data Link Layer) of the OSI model. Its core function is to forward data frames within a single local area network (LAN) segment by learning and using Media Access Control (MAC) addresses. When a frame arrives, the switch consults its MAC address table to determine the correct outgoing port, thereby reducing unnecessary traffic and improving network efficiency compared to hubs. It does not inspect or route based on Layer 3 IP addresses.
B
Bridge
Why it fails: A network bridge is a Layer 2 (Data Link Layer) device designed to connect two separate network segments, effectively creating a single, larger collision domain. Like a switch, it learns MAC addresses of devices on each segment and forwards frames selectively based on the destination MAC address. Bridges are typically simpler than switches, often having fewer ports, but they perform the same fundamental function of segmenting traffic at the MAC address level, not at the IP layer.
C
Router
Routers are fundamental network devices operating at Layer 3 (Network Layer) of the OSI model. They are responsible for forwarding IP packets between different networks or subnets by examining the destination IP address in the packet header. To make intelligent forwarding decisions, a router consults its routing table, which contains information about known network paths and their associated next-hop interfaces. This capability enables communication across disparate networks, forming the backbone of the internet.
D
Hub
Why it fails: A network hub operates at Layer 1 (Physical Layer) of the OSI model, functioning as a multi-port repeater. When a signal arrives at one port, the hub simply regenerates it and broadcasts it out to all other connected ports, regardless of the intended recipient. This lack of intelligence means all devices connected to a hub share a single collision domain, leading to inefficient network traffic and potential performance bottlenecks, as it does not perform any MAC or IP address-based forwarding.

Study the full IPv6 explanation →

Question 11mediummultiple choice

A network engineer is configuring IPv6 on a router interface. Which of the following is a valid global unicast IPv6 address?

Trap 1: fe80::1

The address fe80::1 belongs to the fe80::/10 range, which is reserved for IPv6 link-local addresses. These addresses are automatically configured on every IPv6-enabled interface and are strictly confined to a single network segment or "link." Link-local addresses are essential for neighbor discovery, stateless address autoconfiguration (SLAAC), and other on-link communication but are explicitly not routable beyond that local link by any router.

Trap 2: ff02::1

The address ff02::1 is an IPv6 multicast address, specifically the "all-nodes link-local multicast" address. Multicast addresses are used to send a single packet to multiple destinations simultaneously, rather than to a single unique host. This particular address targets all IPv6-enabled devices on the local link, primarily for discovery protocols, and is not a unicast address that can be assigned to a router interface for point-to-point communication.

Trap 3: ::1

The address ::1 is the IPv6 loopback address, analogous to 127.0.0.1 in IPv4. This special address is exclusively used for a device to send traffic to itself, primarily for testing network applications and services running on the local host. It is not designed for communication with other devices on a network segment or for global routing, making it unsuitable for assignment to a physical router interface.

A
fe80::1
Why it fails: The address fe80::1 belongs to the fe80::/10 range, which is reserved for IPv6 link-local addresses. These addresses are automatically configured on every IPv6-enabled interface and are strictly confined to a single network segment or "link." Link-local addresses are essential for neighbor discovery, stateless address autoconfiguration (SLAAC), and other on-link communication but are explicitly not routable beyond that local link by any router.
B
2001:db8::1
The address 2001:db8::1 is a valid IPv6 global unicast address. It falls within the 2000::/3 range designated for global unicast addresses, making it globally routable across the internet. Specifically, 2001:db8::/32 is reserved by RFC 3849 for use in documentation and example code, ensuring that these addresses will not conflict with actual deployed networks. Therefore, it is a perfectly valid address to assign to a router interface for external communication.
C
ff02::1
Why it fails: The address ff02::1 is an IPv6 multicast address, specifically the "all-nodes link-local multicast" address. Multicast addresses are used to send a single packet to multiple destinations simultaneously, rather than to a single unique host. This particular address targets all IPv6-enabled devices on the local link, primarily for discovery protocols, and is not a unicast address that can be assigned to a router interface for point-to-point communication.
D
::1
Why it fails: The address ::1 is the IPv6 loopback address, analogous to 127.0.0.1 in IPv4. This special address is exclusively used for a device to send traffic to itself, primarily for testing network applications and services running on the local host. It is not designed for communication with other devices on a network segment or for global routing, making it unsuitable for assignment to a physical router interface.

Read the full wireless explanation →

Question 12easymultiple choice

A network engineer is explaining to a manager why wireless networks often have lower throughput than wired Ethernet. Which of the following best describes the primary reason for this difference?

Trap 1: Wireless uses a different MAC method that requires waiting for an…

While wireless protocols often incorporate acknowledgments (ACKs) to confirm successful data reception due to the unreliable nature of the wireless medium, this is not the primary mechanism responsible for the significant reduction in available bandwidth compared to wired Ethernet. The main overhead stems from the proactive collision avoidance mechanisms of CSMA/CA, such as mandatory listening periods (DIFS, SIFS), random backoff timers, and optional RTS/CTS handshakes, which consume substantial airtime even in the absence of actual data transmission.

Trap 2: Wireless operates at half-duplex, while wired Ethernet typically…

It is true that wireless networks typically operate in half-duplex mode, meaning a device cannot transmit and receive simultaneously on the same frequency, largely due to self-interference and the shared medium nature. Conversely, modern wired Ethernet connections commonly operate in full-duplex, allowing simultaneous transmission and reception, which significantly boosts theoretical throughput. However, the half-duplex nature of wireless is a consequence of the physical layer and medium, whereas the primary reason for lower effective throughput is the extensive MAC layer overhead introduced by CSMA/CA's collision avoidance mechanisms.

Trap 3: Wireless signals are subject to interference, but the MAC protocol…

The Medium Access Control (MAC) protocols for wireless and wired Ethernet are fundamentally different. Wired Ethernet uses CSMA/CD (Collision Detection), while wireless networks use CSMA/CA (Collision Avoidance). While wireless signals are indeed susceptible to various forms of interference (e.g., from other Wi-Fi networks, microwaves, Bluetooth), which can degrade throughput, the core architectural difference in their MAC layer protocols is the primary reason for their inherent performance disparity.

A
Wireless uses a different MAC method that requires waiting for an acknowledgment, reducing available bandwidth.
Why it fails: While wireless protocols often incorporate acknowledgments (ACKs) to confirm successful data reception due to the unreliable nature of the wireless medium, this is not the primary mechanism responsible for the significant reduction in available bandwidth compared to wired Ethernet. The main overhead stems from the proactive collision avoidance mechanisms of CSMA/CA, such as mandatory listening periods (DIFS, SIFS), random backoff timers, and optional RTS/CTS handshakes, which consume substantial airtime even in the absence of actual data transmission.
B
Wireless operates at half-duplex, while wired Ethernet typically operates at full-duplex.
Why it fails: It is true that wireless networks typically operate in half-duplex mode, meaning a device cannot transmit and receive simultaneously on the same frequency, largely due to self-interference and the shared medium nature. Conversely, modern wired Ethernet connections commonly operate in full-duplex, allowing simultaneous transmission and reception, which significantly boosts theoretical throughput. However, the half-duplex nature of wireless is a consequence of the physical layer and medium, whereas the primary reason for lower effective throughput is the extensive MAC layer overhead introduced by CSMA/CA's collision avoidance mechanisms.
C
Wireless uses CSMA/CA which involves a collision avoidance mechanism that adds overhead, whereas wired Ethernet uses CSMA/CD which only responds after collision.
This statement is accurate because wireless networks employ Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). This protocol mandates a station to listen for a clear channel, wait for a Distributed Interframe Space (DIFS), and potentially use Request To Send/Clear To Send (RTS/CTS) before transmitting, all of which introduce significant latency and overhead. In contrast, wired Ethernet utilizes CSMA/CD, where stations transmit immediately upon sensing a clear channel and only react to collisions if they occur, making it more efficient in a controlled, detectable collision domain.
D
Wireless signals are subject to interference, but the MAC protocol is identical to Ethernet.
Why it fails: The Medium Access Control (MAC) protocols for wireless and wired Ethernet are fundamentally different. Wired Ethernet uses CSMA/CD (Collision Detection), while wireless networks use CSMA/CA (Collision Avoidance). While wireless signals are indeed susceptible to various forms of interference (e.g., from other Wi-Fi networks, microwaves, Bluetooth), which can degrade throughput, the core architectural difference in their MAC layer protocols is the primary reason for their inherent performance disparity.

Review the full routing breakdown →

Question 13easymultiple choice

At which layer of the OSI model does logical addressing (e.g., IP addresses) and routing occur?

Trap 1: Data Link layer

The Data Link layer uses MAC addresses for node-to-node delivery on a single segment, so it performs no logical addressing or routing between networks. It is tempting because frames do carry addressing, and Data Link would be correct if the question asked where physical addressing and error detection on the local link occur.

Trap 2: Transport layer

The Transport layer handles end-to-end segments, ports and reliability, carrying no logical addressing or routing function. It is tempting because TCP and UDP headers do contain port numbers that identify applications, and Transport would be the correct answer if the question asked where segmentation and flow control occur.

Trap 3: Physical layer

The Physical layer transmits raw bits over the medium, defining voltages, cabling and signalling, with no addressing or routing whatsoever. It is tempting because every routed packet ultimately traverses physical media, and Physical would be correct if the question asked where bit encoding and transmission rates are defined.

A
Data Link layer
Why it fails: The Data Link layer uses MAC addresses for node-to-node delivery on a single segment, so it performs no logical addressing or routing between networks. It is tempting because frames do carry addressing, and Data Link would be correct if the question asked where physical addressing and error detection on the local link occur.
B
Network layer
Logical addressing and routing are the defining functions of the Network layer, where IP addresses identify hosts across networks and routers forward packets between them. The Data Link layer handles physical MAC addressing instead, so it cannot satisfy the routing requirement in the stem.
C
Transport layer
Why it fails: The Transport layer handles end-to-end segments, ports and reliability, carrying no logical addressing or routing function. It is tempting because TCP and UDP headers do contain port numbers that identify applications, and Transport would be the correct answer if the question asked where segmentation and flow control occur.
D
Physical layer
Why it fails: The Physical layer transmits raw bits over the medium, defining voltages, cabling and signalling, with no addressing or routing whatsoever. It is tempting because every routed packet ultimately traverses physical media, and Physical would be correct if the question asked where bit encoding and transmission rates are defined.

Question 14easymultiple choice

Which of the following is a characteristic of a connectionless protocol at the transport layer?

Trap 1: It establishes a session before sending data

Establishing a session, often involving a multi-step handshake process like TCP's three-way handshake, is a hallmark of connection-oriented protocols. This setup phase creates a logical connection and synchronizes sequence numbers and window sizes between the sender and receiver. Connectionless protocols, by their very nature, bypass this session establishment entirely, immediately sending data without any prior negotiation or state synchronization, which reduces latency but sacrifices reliability.

Trap 2: It guarantees delivery using acknowledgments

Connectionless protocols do not guarantee delivery because they lack the necessary mechanisms, such as acknowledgments. An acknowledgment (ACK) is a message sent by the receiver back to the sender to confirm successful receipt of data. Without these acknowledgments, the sender has no confirmation that the data arrived, and therefore cannot ensure its delivery, making the service "best-effort" rather than guaranteed.

Trap 3: It retransmits lost segments

Connectionless protocols, like UDP, do not implement mechanisms for detecting or retransmitting lost data segments. Since they do not maintain connection state or use acknowledgments, they have no way of knowing if a segment reached its destination or if it was dropped en route. This lack of retransmission contributes to their lower overhead and faster transmission, but also means applications relying on them must handle reliability at a higher layer if needed.

A
It establishes a session before sending data
Why it fails: Establishing a session, often involving a multi-step handshake process like TCP's three-way handshake, is a hallmark of connection-oriented protocols. This setup phase creates a logical connection and synchronizes sequence numbers and window sizes between the sender and receiver. Connectionless protocols, by their very nature, bypass this session establishment entirely, immediately sending data without any prior negotiation or state synchronization, which reduces latency but sacrifices reliability.
B
It guarantees delivery using acknowledgments
Why it fails: Connectionless protocols do not guarantee delivery because they lack the necessary mechanisms, such as acknowledgments. An acknowledgment (ACK) is a message sent by the receiver back to the sender to confirm successful receipt of data. Without these acknowledgments, the sender has no confirmation that the data arrived, and therefore cannot ensure its delivery, making the service "best-effort" rather than guaranteed.
C
It does not require a virtual circuit
Connectionless protocols, such as UDP at the transport layer, operate by sending individual data units (datagrams) independently. They do not establish a dedicated, end-to-end logical path, known as a virtual circuit, between the sender and receiver prior to data transmission. Each datagram is treated as a standalone entity, routed based solely on its destination address without any pre-negotiated state or connection setup overhead. This design prioritizes speed and efficiency over reliability.
D
It retransmits lost segments
Why it fails: Connectionless protocols, like UDP, do not implement mechanisms for detecting or retransmitting lost data segments. Since they do not maintain connection state or use acknowledgments, they have no way of knowing if a segment reached its destination or if it was dropped en route. This lack of retransmission contributes to their lower overhead and faster transmission, but also means applications relying on them must handle reliability at a higher layer if needed.

Open the full VLAN trunking answer →

Question 15hardmultiple choice

A network administrator has configured a switch with four VLANs: VLAN 10, 20, 30, and 99 (native). The switch is connected to a router via an 802.1Q trunk link. The router has subinterfaces for VLANs 10, 20, and 30, each with an IP address. VLAN 99 is used for management and does not have a router subinterface. How many Layer 3 broadcast domains exist in this network?

Trap 1: 1

A single Layer 3 broadcast domain would require all VLANs to share one routed subnet, which the 802.1Q trunk and per-VLAN router subinterfaces prevent. Each subinterface on VLANs 10, 20 and 30 creates its own broadcast domain, so one is incorrect.

Trap 2: 2

Incorrect. Two broadcast domains is not accurate given the three routed subinterfaces.

Trap 3: 4

Incorrect. This mistakenly counts VLAN 99, which lacks a router subinterface, as a Layer 3 broadcast domain.

A
1
Why it fails: A single Layer 3 broadcast domain would require all VLANs to share one routed subnet, which the 802.1Q trunk and per-VLAN router subinterfaces prevent. Each subinterface on VLANs 10, 20 and 30 creates its own broadcast domain, so one is incorrect.
B
2
Why it fails: Incorrect. Two broadcast domains is not accurate given the three routed subinterfaces.
C
3
Each router subinterface terminates a VLAN, creating a separate Layer 3 broadcast domain for VLANs 10, 20 and 30. VLAN 99 is native and has no subinterface, so it carries no routed IP segment, leaving three broadcast domains despite four VLANs existing on the trunk.
D
4
Why it fails: Incorrect. This mistakenly counts VLAN 99, which lacks a router subinterface, as a Layer 3 broadcast domain.

Review the full routing breakdown →

Question 16mediumdrag order

Drag and drop the steps to configure a static route on a network router into the correct order.

Drag or tap steps into the slots.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Trap 1: Step 1: Access the router's configuration mode

This order is incorrect because attempting to verify the static route using `show ip route` (Step 2) before it has actually been configured (Step 3) will not yield the desired result. At the point of verification, the new static route does not exist in the router's running configuration or routing table. Therefore, `show ip route` would only display existing routes, making this verification step premature and ineffective for confirming the intended new route.

Trap 2: Step 1: Define the static route with the destination network,…

The `ip route` command, which is used to configure a static route, is a global configuration command. It cannot be executed directly from user EXEC mode or privileged EXEC mode. Attempting to enter the `ip route` command (Step 1) without first entering global configuration mode (`configure terminal`) (Step 2) would result in a command rejection error, preventing any configuration from taking place.

Trap 3: Step 1: Access the router's configuration mode

This sequence is incorrect because saving the configuration (Step 2) occurs prematurely, before the static route has actually been configured (Step 3). When `copy running-config startup-config` is executed, the `running-config` does not yet contain the new static route, meaning the `startup-config` would be updated without the intended change. Consequently, the static route would not be saved, and verifying it after this incorrect save but before configuration would be meaningless.

A
Step 1: Access the router's configuration mode. Step 2: Define the static route with the destination network, subnet mask, and next hop. Step 3: Verify the route appears in the routing table. Step 4: Save the configuration to persistent storage.
This sequence correctly outlines the necessary steps to implement a static route on a Cisco device. First, entering global configuration mode (`configure terminal`) is essential as the `ip route` command is a global configuration command. Next, the `ip route` command is executed to add the static route to the router's running configuration. Subsequently, `show ip route` is used to verify that the route has been successfully added to the routing table and is operational. Finally, `copy running-config startup-config` saves the changes from volatile RAM to non-volatile memory, ensuring the static route persists across reboots.
B
Step 1: Access the router's configuration mode. Step 2: Verify the route appears in the routing table. Step 3: Define the static route with the destination network, subnet mask, and next hop. Step 4: Save the configuration to persistent storage.
Why it fails: This order is incorrect because attempting to verify the static route using `show ip route` (Step 2) before it has actually been configured (Step 3) will not yield the desired result. At the point of verification, the new static route does not exist in the router's running configuration or routing table. Therefore, `show ip route` would only display existing routes, making this verification step premature and ineffective for confirming the intended new route.
C
Step 1: Define the static route with the destination network, subnet mask, and next hop. Step 2: Access the router's configuration mode. Step 3: Verify the route appears in the routing table. Step 4: Save the configuration to persistent storage.
Why it fails: The `ip route` command, which is used to configure a static route, is a global configuration command. It cannot be executed directly from user EXEC mode or privileged EXEC mode. Attempting to enter the `ip route` command (Step 1) without first entering global configuration mode (`configure terminal`) (Step 2) would result in a command rejection error, preventing any configuration from taking place.
D
Step 1: Access the router's configuration mode. Step 2: Save the configuration to persistent storage. Step 3: Define the static route with the destination network, subnet mask, and next hop. Step 4: Verify the route appears in the routing table.
Why it fails: This sequence is incorrect because saving the configuration (Step 2) occurs prematurely, before the static route has actually been configured (Step 3). When `copy running-config startup-config` is executed, the `running-config` does not yet contain the new static route, meaning the `startup-config` would be updated without the intended change. Consequently, the static route would not be saved, and verifying it after this incorrect save but before configuration would be meaningless.

Review the full routing breakdown →

Question 17mediumdrag order

Drag and drop the steps to recover a lost router password on a Cisco device into the correct order.

Drag or tap steps into the slots.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Trap 1: 1

This is incorrect because reloading before changing the register means the router will boot with the original register value, ignoring the registers change, so the startup config will be loaded and you cannot modify it.

Trap 2: 1

Attempting to change the configuration register with the "confreg" command as the first step is incorrect because this command is only accessible from ROMmon mode. To enter ROMmon, the boot sequence must first be interrupted. Without this initial interruption, the router will proceed with its normal boot process, making the "confreg" command unavailable and resulting in an unrecognized command error, thus preventing any progress in the password recovery procedure.

Trap 3: 1

This sequence is flawed from the outset because the "confreg" command, used to modify the configuration register, is a utility exclusive to the ROM Monitor (ROMmon) environment. It is impossible to execute this command from the normal operating system or during the initial boot phase before ROMmon has been accessed. Therefore, attempting to change the register as the very first action, prior to interrupting the boot sequence to enter ROMmon, will fail, rendering the entire recovery process ineffective.

A
1. Interrupt boot sequence, 2. Change configuration register to 0x2142, 3. Reload router, 4. Copy startup-config to running-config, 5. Change enable password, 6. Reset configuration register to 0x2102, 7. Save running-config, 8. Reload router
This order is correct because you must first halt the boot to access ROMmon, then set the register to ignore startup config, reload to load the OS without config, copy the config to modify it, change the password, save, reset the register to boot normally, and final reload.
B
1. Interrupt boot sequence, 2. Reload router, 3. Change configuration register to 0x2142, 4. Copy startup-config to running-config, 5. Change enable password, 6. Save running-config, 7. Reset configuration register to 0x2102, 8. Reload router
Why it fails: This is incorrect because reloading before changing the register means the router will boot with the original register value, ignoring the registers change, so the startup config will be loaded and you cannot modify it.
C
1. Change configuration register to 0x2142, 2. Reload router, 3. Interrupt boot sequence, 4. Copy startup-config to running-config, 5. Change enable password, 6. Save running-config, 7. Reset configuration register to 0x2102, 8. Reload router
Why it fails: Attempting to change the configuration register with the "confreg" command as the first step is incorrect because this command is only accessible from ROMmon mode. To enter ROMmon, the boot sequence must first be interrupted. Without this initial interruption, the router will proceed with its normal boot process, making the "confreg" command unavailable and resulting in an unrecognized command error, thus preventing any progress in the password recovery procedure.
D
1. Change configuration register to 0x2142, 2. Interrupt boot sequence, 3. Reload router, 4. Copy startup-config to running-config, 5. Change enable password, 6. Save running-config, 7. Reset configuration register to 0x2102, 8. Reload router
Why it fails: This sequence is flawed from the outset because the "confreg" command, used to modify the configuration register, is a utility exclusive to the ROM Monitor (ROMmon) environment. It is impossible to execute this command from the normal operating system or during the initial boot phase before ROMmon has been accessed. Therefore, attempting to change the register as the very first action, prior to interrupting the boot sequence to enter ROMmon, will fail, rendering the entire recovery process ineffective.

Question 18mediummatching

Match each network device to its primary function.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

Forwards packets between different networks based on IP addresses

Forwards frames within the same network based on MAC addresses

Filters traffic based on security rules

Connects wireless clients to a wired network

Trap 1: Modem: Connects multiple networks and routes data packets between…

Incorrect — a modem modulates/demodulates signals for internet access, not routing.

Trap 2: Hub: Connects devices within a single network and forwards data…

Incorrect — a hub repeats signals to all ports, not forwarding based on MAC addresses (that's a switch).

A
Router: Connects multiple networks and routes data packets between them.
Routers operate at Layer 3 and use IP addresses to forward packets between different networks.
B
Switch: Connects devices within a single network and forwards data based on MAC addresses.
Switches operate at Layer 2 and use MAC addresses to efficiently direct frames to specific devices.
C
Firewall: Monitors and controls incoming/outgoing network traffic based on security rules.
Firewalls enforce security policies by permitting or denying traffic based on rules.
D
Access Point: Allows wireless devices to connect to a wired network.
Access points bridge wireless clients to a wired LAN, often using Wi-Fi.
E
Modem: Connects multiple networks and routes data packets between them.
Why it fails: Incorrect — a modem modulates/demodulates signals for internet access, not routing.
F
Hub: Connects devices within a single network and forwards data based on MAC addresses.
Why it fails: Incorrect — a hub repeats signals to all ports, not forwarding based on MAC addresses (that's a switch).

Open the full VLAN trunking answer →

Question 19hardmulti select

A network administrator is configuring a switch that will connect to a router and several access points. The administrator needs to ensure that the switch ports carrying traffic for multiple VLANs can pass frames for all VLANs while keeping broadcast domains separate. The administrator also wants to reduce manual configuration on the switch. Which two actions should the administrator take? (Choose two.)

Trap 1: Configure the switch ports connected to end-user workstations as…

Access ports belong to a single VLAN and are used for end devices that do not need to tag VLAN traffic. While this is a common practice, it does not help the switch pass traffic for multiple VLANs across the links to the router and access points. It also does not reduce configuration on the switch; it is standard practice but not what the scenario requires.

Trap 2: Configure the native VLAN to match on all trunk ports.

Matching the native VLAN on trunk ports is a best practice to avoid VLAN mismatch errors, but it does not itself enable multiple VLANs to pass. The native VLAN handles untagged traffic on a trunk. While important for security and consistency, it is not one of the two actions required to allow multiple VLANs to traverse the links.

Trap 3: Enable VTP in server mode on the switch to propagate VLAN…

VTP can reduce manual VLAN configuration by propagating VLANs between switches, but the scenario mentions a single switch connecting to a router and access points, not multiple switches needing VLAN propagation. VTP does not enable multiple VLANs on a single link; trunking does that. Therefore, VTP is not the correct action here.

A
Configure the switch ports connected to the router and access points as trunk ports.
Trunk ports carry traffic for multiple VLANs by tagging frames with 802.1Q VLAN identifiers. Connecting a router and access points that need to serve multiple VLANs requires trunk links so that each VLAN's traffic can traverse the link while remaining logically separate. This directly addresses the need to pass traffic for all VLANs.
B
Configure the switch ports connected to end-user workstations as access ports in the appropriate VLAN.
Why it fails: Access ports belong to a single VLAN and are used for end devices that do not need to tag VLAN traffic. While this is a common practice, it does not help the switch pass traffic for multiple VLANs across the links to the router and access points. It also does not reduce configuration on the switch; it is standard practice but not what the scenario requires.
C
Configure the native VLAN to match on all trunk ports.
Why it fails: Matching the native VLAN on trunk ports is a best practice to avoid VLAN mismatch errors, but it does not itself enable multiple VLANs to pass. The native VLAN handles untagged traffic on a trunk. While important for security and consistency, it is not one of the two actions required to allow multiple VLANs to traverse the links.
D
Enable VTP in server mode on the switch to propagate VLAN configurations to other switches.
Why it fails: VTP can reduce manual VLAN configuration by propagating VLANs between switches, but the scenario mentions a single switch connecting to a router and access points, not multiple switches needing VLAN propagation. VTP does not enable multiple VLANs on a single link; trunking does that. Therefore, VTP is not the correct action here.
E
Use 802.1Q encapsulation on the trunk links to tag frames with VLAN IDs.
802.1Q is the standard trunking encapsulation that inserts a VLAN tag into Ethernet frames, allowing multiple VLANs to share a physical link. Configuring trunk ports with 802.1Q is essential for carrying traffic for multiple VLANs between the switch, router, and access points. This is a correct action for the scenario.

Question 20easymultiple choice

A network administrator is troubleshooting a connectivity issue and suspects the problem is related to the physical cabling. At which layer of the OSI model should the administrator begin their investigation?

Trap 1: Transport layer

The Transport layer (Layer 4) provides end-to-end communication services between applications, including segmentation, reassembly, flow control, and error recovery (for TCP). It operates logically between two host processes, ensuring data delivery across the network. A problem at this layer would typically involve issues like blocked ports, incorrect firewall rules preventing application communication, or application-level protocol errors, assuming the underlying network connectivity (including physical cabling) is already established and functional.

Trap 2: Data Link layer

The Data Link layer (Layer 2) is responsible for reliable data transfer across a direct link, handling framing, error detection within frames, and Media Access Control (MAC) addressing. While it interacts with the Physical layer, its concerns are logical link establishment and managing access to the shared medium, not the physical integrity of the cable itself. Problems at this layer typically involve MAC address conflicts, incorrect frame formatting, or issues with switches and network interface cards (NICs) that prevent proper frame delivery, assuming the underlying physical connection is sound.

Trap 3: Network layer

The Network layer handles logical addressing and routing decisions, not physical cabling faults. The administrator suspects a cable issue, which manifests as signal degradation or electrical problems at the Physical layer (Layer 1). This option is tempting because network-layer troubleshooting often involves connectivity failures, but those stem from IP misconfiguration or routing loops, not from the physical medium itself.

A
Transport layer
Why it fails: The Transport layer (Layer 4) provides end-to-end communication services between applications, including segmentation, reassembly, flow control, and error recovery (for TCP). It operates logically between two host processes, ensuring data delivery across the network. A problem at this layer would typically involve issues like blocked ports, incorrect firewall rules preventing application communication, or application-level protocol errors, assuming the underlying network connectivity (including physical cabling) is already established and functional.
B
Data Link layer
Why it fails: The Data Link layer (Layer 2) is responsible for reliable data transfer across a direct link, handling framing, error detection within frames, and Media Access Control (MAC) addressing. While it interacts with the Physical layer, its concerns are logical link establishment and managing access to the shared medium, not the physical integrity of the cable itself. Problems at this layer typically involve MAC address conflicts, incorrect frame formatting, or issues with switches and network interface cards (NICs) that prevent proper frame delivery, assuming the underlying physical connection is sound.
C
Physical layer
The Physical layer (Layer 1) is fundamentally responsible for the raw bit stream transmission over the physical medium, defining the electrical, mechanical, and procedural specifications for transmitting data signals. Therefore, issues such as faulty cables, damaged connectors, incorrect cable types, or signal degradation due to attenuation or electromagnetic interference directly manifest as problems at this foundational layer, preventing any higher-layer communication from occurring reliably or at all.
D
Network layer
Why it fails: The Network layer handles logical addressing and routing decisions, not physical cabling faults. The administrator suspects a cable issue, which manifests as signal degradation or electrical problems at the Physical layer (Layer 1). This option is tempting because network-layer troubleshooting often involves connectivity failures, but those stem from IP misconfiguration or routing loops, not from the physical medium itself.