Which of the following network devices permits and restricts network traffic as its primary function?

The CompTIA Tech+ Study Guide explains:

“Firewalls filter network traffic. Firewalls filter inbound and outbound network traffic based on rules defined by the administrator. That list of rules is called an access control list (ACL). By default, most firewalls are configured as default deny, which means that all traffic is blocked unless specifically authorized by the administrator.”

Therefore, a firewall is the network security device that primarily permits and restricts traffic based on predefined rules.

Verified Reference:

Chapter 5: Software Applications — “Software Firewalls” (pp. 316–317).

Chapter 8: Networking Concepts and Technologies — “Firewalls” (pp. 447–448).