The best security measure to implement when removing a computer from a cubicle is to remove the employee's network access. This will prevent the employee from accessing any network resources or data from the computer, as well as prevent any unauthorized users from using the computer to access the network.
Removing the employee's network access can be done by deleting or disabling the user account, revoking the credentials, or changing the permissions.
The other options are not as effective or necessary as removing the employee's network access. They are:
*Disabling DHCP on the computer being removed will prevent the computer from obtaining an IP address from the network, but it will not prevent the computer from using a static IP address or accessing the network through another device.
*Placing the switch port in a private VLAN will isolate the computer from other devices on the network, but it will not prevent the computer from accessing the network through another port or device.
*Applying a firewall rule to block the computer's IP address will prevent the computer from communicating with the network, but it will not prevent the computer from changing its IP address or accessing the network through another device.
References
1: CompTIA Network+ N10-008 Cert Guide - O'Reilly Media
2: Network+ (Plus) Certification | CompTIA IT Certifications
3: 10 Ways to Secure Office Workstations - Computer Security