Afirewall can consist of all devices positioned on the network

The answer to this question is "perimeter".

Explanation:

In computer science, the firewall is used to provide a network security system that manages network traffic like incoming and outgoing signals. This traffics is based on predetermined security rules. The firewall typically installs a boundary between a trusted inner network and an untrusted outer network, such as the Internet. It is a software concept and Perimeter firewalls manage the flow of network traffic and host or organization's border the boundary that provides the first line of security against outer attacks and blocking access to inappropriate content from inside an organization.