A company has attempted to introduce a new major network segment to allow growth in capacity. On the core switch, a GBIC was used to interconnect with a newly placed downstream distribution switch for the first time. Soon after this implementation, a network flood and an outage occurred between the core and new distribution network modules. Which of the following should the network administrator troubleshoot FIRST in order to rectify the issue?

A. Check for switching loops between core and distribution switches.
B. Check whether an incorrect VLAN has been assigned to the new distribution switch.
C. Check for inconsistent or missing routes between the core and distribution switches.
D. Check whether the GBIC was set to multi-mode instead of single-mode SFP.

Answer: A. Check for switching loops between core and distribution switches.