Which technology allows you to block network access based on the application being used to initiate the request?

The correct choice is host-based firewall, as this type of firewall is specifically designed to monitor and control incoming and outgoing network traffic on an individual device based on application-level traffic. Host-based firewalls can evaluate application behaviors and block or allow network access contingent upon the specific application that is trying to send or receive data.

This capability enables a more granular level of security by allowing or denying access based on specific applications rather than just IP addresses or ports. Such firewalls are typically implemented on individual computers or endpoints, offering additional protection against threats that originate from compromised applications.

Other options do not have the same focus or capability. Routers primarily handle traffic routing and can have basic filtering capabilities, but they do not incorporate application awareness to the same extent. Network firewalls usually operate at the network and transport layers and generally filter traffic based on criteria like IP addresses and ports rather than specific applications. Application layer gateways (also known as application proxies) can analyze traffic at the application layer, but they tend to serve a different function by acting as intermediaries between clients and servers, rather than just blocking access based on application use.