N10-009 Networking Concepts — 20 Questions

Question 1

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?

Accepted Answer

192.168.1.128. The network address is found by performing a bitwise AND between the IP address 192.168.1.130 and the subnet mask 255.255.255.192. The mask 255.255.255.192 has a prefix length of /26, meaning the first 26 bits are the network portion. 192.168.1.130 in binary is 11000000.10101000.00000001.10000010, and the mask is 11111111.11111111.11111111.11000000; the AND yields 11000000.10101000.00000001.10000000, which is 192.168.1.128.

Answer

192.168.1.0

Answer

192.168.1.192

Answer

192.168.1.64

Question 2

A network technician is assigned a subnet mask of 255.255.255.248. How many usable host addresses are available in this subnet?

Accepted Answer

A) 6. The subnet mask 255.255.255.248 corresponds to a /29 prefix length, which provides 2^(32-29) = 8 total addresses. Subtracting the network address and broadcast address leaves 8 - 2 = 6 usable host addresses.

Answer

B) 8

Answer

C) 14

Answer

D) 30

Question 3

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

Accepted Answer

/28. A /28 subnet mask (255.255.255.240) provides 16 total addresses per subnet. Subtracting the network address and broadcast address leaves 14 usable host addresses, which exactly meets the requirement of at least 10 hosts.

Answer

/27

Answer

/29

Answer

/30

Question 4

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?

Accepted Answer

TCP. TCP (Transmission Control Protocol) is the correct choice because it provides reliable, connection-oriented data transfer with error checking, retransmission of lost packets, and in-order delivery. For a large database file transfer across a WAN link, TCP ensures the data arrives completely and without errors, which is essential for database integrity.

Answer

UDP

Answer

IP

Answer

ICMP

Question 5

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?

Accepted Answer

255.255.255.224 (/27). (255.255.255.224, /27) provides 32 total addresses per subnet, with 30 usable host addresses (2^(32-27)-2 = 30). This is the smallest subnet that can accommodate exactly 25 devices, as /28 yields only 14 usable hosts and /26 yields 62, which is excessive.

Answer

255.255.255.240 (/28)

Answer

255.255.255.192 (/26)

Answer

255.255.255.128 (/25)

Question 6

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?

Accepted Answer

255.255.255.192 (/26). (255.255.255.192, /26) provides 2^(32-26) - 2 = 62 usable host addresses, which is the smallest subnet that supports exactly 50 devices. A /27 yields only 30 usable addresses (too few), while a /25 yields 126 usable addresses (wasteful). The requirement is to minimize waste while meeting the need.

Answer

255.255.255.128 (/25)

Answer

255.255.255.224 (/27)

Answer

255.255.255.240 (/28)

Question 7

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?

Accepted Answer

Router. A router operates at Layer 3 (Network layer) of the OSI model and makes forwarding decisions based on IP addresses. It uses routing tables and protocols such as OSPF or BGP to determine the best path for packets between different networks. This makes it the correct device for connecting two distinct networks and forwarding traffic by IP address.

Answer

Hub

Answer

Switch

Answer

Bridge

Question 8

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

Accepted Answer

B. A /26 subnet mask (255.255.255.192) provides 62 usable host addresses (2^(32-26) - 2 = 64 - 2 = 62), which is the smallest subnet that supports at least 50 hosts. A /27 would only provide 30 usable addresses, which is insufficient.

Answer

A

Answer

C

Answer

D

Question 9

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?

Accepted Answer

The OSPF cost of the primary link is higher than the backup link.. OSPF determines the best path using cost, which is calculated as (reference bandwidth) / (interface bandwidth). By default, the reference bandwidth is 100 Mbps. For a 1 Gbps link, the cost is 0.1, which is rounded up to 1. For a 100 Mbps link, the cost is exactly 1. This would normally result in equal-cost paths and load balancing, not preferring the backup link. However, if the router is sending traffic over the backup link, it indicates that the primary link has a higher OSPF cost than the backup. This can happen if the bandwidth statement on the primary interface is misconfigured to a value that results in a higher OSPF cost (e.g., set to 50 Mbps, making its cost 2), or if a manual cost is set higher on the primary interface, or lower on the backup interface. Thus, the most likely cause is that the primary link’s OSPF cost is higher than expected, causing the router to prefer the backup link.

Answer

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

Answer

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

Answer

The bandwidth command is misconfigured on the backup interface.

Question 10

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

Accepted Answer

Router. A router operates at Layer 3 (Network layer) of the OSI model and uses the destination IP address in the packet header to make forwarding decisions. It maintains a routing table (e.g., via OSPF, EIGRP, or static routes) to determine the next-hop interface for each packet, enabling communication between different subnets or VLANs.

Answer

Switch

Answer

Bridge

Answer

Hub

Question 11

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

Accepted Answer

2001:db8::1. 2001:db8::1 is a valid global unicast IPv6 address because it falls within the 2000::/3 range defined by RFC 4291 for global unicast addresses. The address is routable on the public internet, making it suitable for global communication.

Answer

fe80::1

Answer

ff02::1

Answer

::1

Question 12

Which of the following best describes the primary function of a subnet mask in IPv4 networking?

Accepted Answer

It identifies which part of an IP address is the network address and which part is the host address. The subnet mask is a 32-bit value that separates the IP address into network and host portions through a bitwise AND operation. This allows routers and hosts to determine whether a destination IP is on the same local network or requires forwarding to a default gateway. Without the subnet mask, a device cannot distinguish the network prefix from the host identifier, making routing impossible.

Answer

It dynamically assigns IP addresses to devices on the network

Answer

It encrypts data packets to ensure secure communication

Answer

It specifies the IP address of the router that forwards traffic to other networks

Question 13

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?

Accepted Answer

Wireless uses CSMA/CA which involves a collision avoidance mechanism that adds overhead, whereas wired Ethernet uses CSMA/CD which only responds after collision.. Wireless networks use CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), which requires stations to perform a four-way handshake (RTS/CTS) and wait for an acknowledgment before transmitting. This collision avoidance mechanism introduces significant overhead, reducing effective throughput. In contrast, wired Ethernet uses CSMA/CD, which detects collisions after they occur and does not require such proactive overhead, allowing higher throughput.

Answer

Wireless uses a different MAC method that requires waiting for an acknowledgment, reducing available bandwidth.

Answer

Wireless operates at half-duplex, while wired Ethernet typically operates at full-duplex.

Answer

Wireless signals are subject to interference, but the MAC protocol is identical to Ethernet.

Question 14

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

Accepted Answer

It does not require a virtual circuit. Connectionless protocols at the transport layer, such as UDP (User Datagram Protocol), do not establish a virtual circuit or session before sending data. Each datagram is sent independently without prior coordination, making the protocol stateless and reducing overhead. This characteristic is fundamental to UDP's design, as defined in RFC 768.

Answer

It establishes a session before sending data

Answer

It guarantees delivery using acknowledgments

Answer

It retransmits lost segments

Question 15

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

Accepted Answer

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.. To configure a static route, first access the router's configuration mode, then define the static route with the destination network, subnet mask, and next hop address. After configuration, verify that the route appears in the routing table, and finally save the configuration to persistent storage so it remains after a reboot.

Answer

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.

Answer

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.

Answer

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.

Question 16

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

Accepted Answer

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. The provided explanation is too generic and does not justify the specific order of steps, particularly the incorrect sequence of saving the running-config before resetting the configuration register to 0x2102. For a successful Cisco password recovery, the configuration register must be reset to 0x2102 in global configuration mode, and *then* the running-config (which now includes the new password and the correct register setting) must be saved to NVRAM. If saved before resetting the register, the router will continue to boot bypassing the startup-config on subsequent reloads.

Answer

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

Answer

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

Answer

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

Question 17

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?

Accepted Answer

Physical layer. The Physical layer (Layer 1) is the correct starting point because the administrator suspects the problem is related to physical cabling. The Physical layer defines the electrical, mechanical, and procedural specifications for transmitting raw bits over a physical medium, such as copper or fiber optic cables. Troubleshooting at this layer involves checking for cable faults, signal degradation, or improper termination before moving up the OSI stack.

Answer

Transport layer

Answer

Data Link layer

Answer

Network layer

Question 18

A network technician is explaining the concept of encapsulation to a junior technician. At which OSI layer does a packet get encapsulated with a source and destination IP address?

Accepted Answer

Layer 3. At Layer 3 (the Network layer), the packet is encapsulated with a source and destination IP address. This is defined by the Internet Protocol (IP), which handles logical addressing and routing across networks. The IP header is added to the payload from the upper layers, creating a packet that can be forwarded by routers.

Answer

Layer 2

Answer

Layer 4

Answer

Layer 1

Question 19

A network engineer is designing a new IPv6 addressing scheme. The company has been assigned a /48 prefix and needs to support up to 250 subnets. Which subnet size should be used to minimize waste while meeting the requirement?

Accepted Answer

/56. A /56 subnet provides 256 subnets (2^(56-48) = 2^8 = 256), which meets the requirement of up to 250 subnets with minimal waste. A /48 prefix is the site-level allocation, and using a /56 subnet mask leaves 8 bits for subnetting, offering exactly the needed capacity without over-allocating address space.

Answer

/52

Answer

/64

Answer

/60

Question 20

A network technician is explaining the difference between a hub and a switch to a junior technician. Which statement correctly describes a key difference between these devices?

Accepted Answer

A hub sends frames out all ports except the incoming port; a switch sends frames only to the port with the matching MAC address.. B is correct because a hub operates at Layer 1 (physical layer) and blindly repeats electrical signals out all ports except the incoming port, creating a single collision domain. In contrast, a switch operates at Layer 2 (data link layer) and uses the MAC address table to forward frames only to the specific port associated with the destination MAC address, reducing unnecessary traffic and creating separate collision domains per port.

Answer

A hub operates at Layer 2, while a switch operates at Layer 1.

Answer

A hub uses MAC addresses to make forwarding decisions, while a switch uses IP addresses.

Answer

A hub creates a separate collision domain for each port, while a switch creates a single collision domain.