$3$ A firewall is a network security device that monitors incoming and outgoing network traffic and decides whether to allow or block specific traffic based on a defined set of security rules.

Firewalls have been a first line of defense in network security for over $25$ years. They establish a barrier between secured and controlled internal networks that can be trusted and untrusted outside networks, such as the Internet. A firewall can be hardware, software, software$-$as$-$a service $($SaaS$),$ public cloud, or private cloud $($virtual$).$

Discuss $5$ types of firewalls which are commonly used in network security, and how does each type differ in terms of functionality and effectiveness in safeguarding against cyber threats?