Each DHCP request with a different MAC address is regarded by the DHCP server as a new network client request. If the attacker sends an ample number of requests, the server's address pool will ultimately be exhausted. Hence, new network clients will be denied the DHCP service and will be unable to join the network.

Port security is a feature that allows a network device to limit the number and type of MAC addresses that can access a port. Port security can prevent unauthorized devices from connecting to the network through an available network jack. Therefore, port security is the most likely cause of the connectivity issues for some mobile users in the new lobby.

A network technician should follow a network troubleshooting methodology to systematically identify and resolve network problems12.
A network troubleshooting methodology consists of several steps, such as identifying the problem, establishing a theory of probable cause, testing the theory, implementing a solution, verifying functionality, and documenting the results12.
In this scenario, the network technician has determined the cause of a network disruption, which means that they have completed the steps of identifying the problem, establishing a theory of probable cause, and testing the theory12.
The NEXT step for the technician to perform is to establish a plan of action to resolve the issue, which means that they should define the steps, resources, and tools needed to implement a solution that can fix the network disruption12.
Establishing a plan of action to resolve the issue is the next step, because it can help the technician to prepare for the implementation, avoid potential risks or complications, and communicate the plan to the stakeholders12.
The other options are not the next step for the technician to perform, because they are either previous or subsequent steps in the network troubleshooting methodology12:
A . Validating the findings in a top-to-bottom approach is a previous step, which is part of testing the theory of probable cause, where the technician should verify the network functionality and connectivity from the physical layer to the application layer12.
B . Duplicating the issue, if possible, is a previous step, which is part of identifying the problem, where the technician should reproduce the symptoms and scope of the problem to confirm its existence and impact12.
D . Documenting the findings and actions is a subsequent step, which is part of verifying functionality and preventing recurrence, where the technician should record the problem description, solution, and outcome for future reference and improvement12.
Reference:
1: Network Troubleshooting Methodology - N10-008 CompTIA Network+ : 5.1
2: CompTIA Network+ N10-008 Full Course for Beginners - Network Troubleshooting Methodology (5.1)