A junior administrator replaced an old 10/100 switch with a 10/100/1000 switch in the datacenter and migrated all file server connections. Since then, throughput has significantly degraded. A senior network administrator looked at the interfaces and noticed a significant number of collisions and errors. Which of the following is the MOST likely reason for the erratic behavior?
A. Duplex mismatch
B. Faulty cabling
C. Improper VLAN configuration
D. Improper tagging/untagging of ports