A zero trust network is a network in which users and devices need to mutually authenticate before any network resource can be accessed. A zero trust network assumes that no one and nothing can be trusted by default, even if they were previously verified or are within the network perimeter. A zero trust network uses various technologies and practices, such as data and log aggregation, cybersecurity analytics, continuous diagnostics and mitigation, user behavior analytics, microsegmentation, and identity and access management, to enforce granular and dynamic policies based on the context and behavior of the users and devices123.
Reference:
What is Zero Trust? | Internet of Things | CompTIA3
The Death of the Perimeter: Zero Trust is (Almost) Here to Stay | Cybersecurity | CompTIA2 CompTIA Network+ Certification Exam N10-008 Practice Test 17 - ExamCompass1

CRC stands for cyclic redundancy check, which is a method of detecting errors in data transmission. CRC errors occur when the verification code calculated by the sender and the receiver do not match, indicating that some bits were corrupted during the transmission.
CRC errors are usually caused by physical layer issues, such as noise, interference, or damaged cables. Therefore, option A is the most likely cause of these errors, as a bad wire on the Cat 5e cable can introduce noise or interference that corrupts the data bits.
Option B is not a likely cause of CRC errors, as the wrong VLAN assignment to the switchport would affect the logical layer, not the physical layer. The wrong VLAN assignment would prevent the switch from forwarding the frames to the correct destination, but it would not cause errors in the data bits themselves.
Option C is also not a likely cause of CRC errors, as a misconfigured QoS setting on the router would affect the network layer, not the physical layer. A misconfigured QoS setting would affect the priority or bandwidth allocation of the packets, but it would not cause errors in the data bits themselves.
Option D is also not a likely cause of CRC errors, as both sides of the switch trunk set to full duplex would not introduce any errors in the data transmission. Full duplex means that both sides can send and receive data simultaneously, without causing collisions or interference. In fact, full duplex is the preferred mode for switch trunks, as it increases the bandwidth and efficiency of the link.
Reference:
CompTIA Network+ N10-008 Study Guide, Chapter 2: Network Devices and Technologies, Section 2.2: Troubleshooting Common Network Problems, Page 941 Professor Messer's CompTIA N10-008 Network+ Course Notes, Section 2.2: Troubleshooting Common Network Problems, Page 162 Solved: [How to resolve] CRC errors - Cisco Community3 Troubleshooting CRC Error Packets on an Interface - Huawei4 Resolving CRC and Input Errors, A Beginner's Guide - site5

The correct tool for verifying existing network connections on a server is C. Netstat. Netstat (network statistics) displays active network connections, routing tables, interface statistics, masquerade connections, and multicast memberships.
Tracert: Tracert (traceroute) is used to trace the route taken by packets from the source to the destination. It helps identify the path and latency between routers.
Ipconfig: Ipconfig is used to view and manage IP configuration settings on a local machine (such as IP address, subnet mask, default gateway, etc.). It does not provide information about existing connections.
Netstat: Netstat displays active network connections, including listening ports, established connections, and associated processes. It's useful for troubleshooting and monitoring network activity.
Nslookup: Nslookup is used for DNS (Domain Name System) queries to resolve domain names to IP addresses. It does not provide information about existing connections.
Reference:
CompTIA Network+ Certification Exam Objectives

A customer needs six usable IP addresses, which means they need a subnet that can accommodate at least six hosts, excluding the network address and the broadcast address12.
The subnet mask determines how many bits are used for the network prefix and how many bits are used for the host identifier12. The more bits are used for the network prefix, the fewer bits are available for the host identifier, and vice versa12.
The number of usable IP addresses in a subnet can be calculated by subtracting two from the number of possible host identifiers, which is 2^(number of host bits)12.
For example, a subnet mask of 255.255.255.0 (/24 in CIDR notation) has 24 bits for the network prefix and 8 bits for the host identifier. Therefore, the number of usable IP addresses in this subnet is 2^8 - 2 = 25412.
The four options in the question have different subnet masks, which correspond to different numbers of usable IP addresses, as shown in the table below:
Table
Subnet mask
CIDR notation
Number of host bits
Number of usable IP addresses
255.255.255.128
/25
7
126
255.255.255.192
/26
6
62
255.255.255.224
/27
5
30
255.255.255.240
/28
4
14
Therefore, the best option that meets the customer's requirement of six usable IP addresses is C. 255.255.255.224, which has 30 usable IP addresses in the subnet12.
Reference:
1: Subnet Cheat Sheet - 24 Subnet Mask, 30, 26, 27, 29, and other IP Address CIDR Network Reference
2: Network Subnets (CIDR) and Usable IP Addresses Reference Guide

An optical time-domain reflectometer (OTDR) is a device that can measure the characteristics of an optical fiber, such as its length, attenuation, and splice points12.
An OTDR works by sending a pulse of light into one end of the fiber and measuring the amount of light that is reflected back at different intervals12.
By analyzing the reflected light, an OTDR can determine the distance to any faults or breaks in the fiber, as well as the overall quality of the fiber12.
An OTDR can also provide a graphical representation of the fiber, called a trace, that shows the attenuation and reflection along the fiber12.
Using an OTDR can reduce repair time because it can quickly and accurately locate the fault point in the fiber, without requiring access to both ends of the fiber12.
The other options are not suitable for testing fiber optic cables:
A tone generator and wire map are tools that can test copper cables, such as twisted-pair or coaxial cables, by sending an electrical signal and identifying the wire pairs3. They cannot test fiber optic cables, which use light instead of electricity1.
A multimeter is a device that can measure electrical properties, such as voltage, current, and resistance4. It cannot test fiber optic cables, which do not carry electrical signals1.
A spectrum analyzer is a device that can measure the frequency and amplitude of electromagnetic signals, such as radio waves or light waves5. It can be used to test the wavelength and power of the light source in a fiber optic cable, but it cannot measure the length or quality of the fiber1.
Reference:
1: Optical Fiber - N10-008 CompTIA Network+ : 1.3
2: CompTIA Network+ N10-008 Full Course for Beginners - Fiber Optic Cabling and Connectors
3: Wire Crimpers and Testers - N10-008 CompTIA Network+ : 1.3
4: Multimeter - N10-008 CompTIA Network+ : 1.3
5: Spectrum Analyzer - N10-008 CompTIA Network+ : 1.3