When the hosts file is altered, local name resolution is compromised, and domain queries are redirected to malicious IP addresses. This is a form of DNS spoofing/poisoning, where false mappings trick users into visiting fraudulent websites.
* B. Phishing typically uses emails or messages to trick users, not local file modification.
* C. VLAN hopping is a Layer 2 attack to gain unauthorized network access, unrelated to DNS.
* D. ARP poisoning manipulates ARP tables on a LAN to reroute traffic, not name resolution.
References (CompTIA Network+ N10-009):
* Domain: Network Security - DNS poisoning/spoofing, host file manipulation, endpoint attacks.

The most likely issue is a duplex mismatch, which is a well-documented cause of collisions and poor network performance, as outlined in the CompTIA Network+ N10-009 troubleshooting objectives. A duplex mismatch occurs when one end of a network link is configured for full duplex while the other end is operating in half duplex. In half-duplex mode, devices must take turns transmitting and receiving data, which inherently allows for collisions. When paired with a full-duplex device-which expects simultaneous send and receive- collisions and retransmissions occur frequently.
The presence of collisions on a switch interface is a key diagnostic clue. Modern Ethernet switches operating correctly in full duplex should not experience collisions at all. When collisions are observed, it almost always points to a duplex configuration issue, often caused by manual speed/duplex settings on one device and auto- negotiation on the other.
A wrong speed setting may prevent link establishment entirely or cause errors, but it does not typically result in collisions. Jumbo frames can cause packet drops or fragmentation issues, not collisions. An incorrect VLAN configuration affects logical segmentation and connectivity but operates at Layer 2 and does not generate collisions.
CompTIA Network+ emphasizes duplex mismatch as a classic and frequently tested troubleshooting scenario.
Correcting it-usually by enabling auto-negotiation on both ends-restores normal, collision-free communication.

Introduction to Disaster Recovery Concepts:
Disaster recovery involves strategies and measures to ensure business continuity and data recovery in the event of a disaster.
Mean Time Between Failures (MTBF):
MTBF is a reliability metric used to predict the time between failures of a system during operation. It is calculated by dividing the total operational time by the number of failures.
Formula: MTBF=Total Operational TimeNumber of Failures\text{MTBF} = \frac{\text{Total Operational Time}}{\text{Number of Failures}}MTBF=Number of FailuresTotal Operational Time This metric helps in understanding the reliability and expected lifespan of systems and components.
Example Calculation:
If a server operates for 1000 hours and experiences 2 failures, the MTBF is: MTBF=1000 hours2=500 hours\text{MTBF} = \frac{1000 \text{ hours}}{2} = 500 \text{ hours}MTBF=21000 hours=500 hours Explanation of the Options:
A . MTTR (Mean Time to Repair): The average time required to repair a system after a failure.
B . MTBF (Mean Time Between Failures): The correct answer, representing the average time between failures.
C . RPO (Recovery Point Objective): The maximum acceptable amount of data loss measured in time.
D . RTO (Recovery Time Objective): The target time set for the recovery of IT and business activities after a disaster.
Conclusion:
MTBF is a crucial metric in disaster recovery and system reliability, helping organizations plan maintenance and predict system performance.
Reference:
CompTIA Network+ guide explaining MTBF, MTTR, RPO, and RTO concepts and their calculations (see page Ref 10fHow to Use Cisco Packet Tracer).

VLANs (Virtual Local Area Networks) segment network traffic by department, allowing ACLs (Access Control Lists) to be applied based on VLAN membership, improving security and resource isolation.