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.
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
