Final answer:
To allow communication between two segments in a segmented network, a router is required. The router directs data packets to a specific network segment based upon IP addresses, functioning at the network layer of the OSI model.
Step-by-step explanation:
If two segments need to talk to each other in a segmented network, the required device is a router. A router helps forward data packets between different network segments. It acts as a dispatching manager that sends data along the most efficient path to reach its destination. This device operates at the network layer of the OSI model, making routing decisions based upon IP addresses.
Other options mentioned, such as a Firewall, Web Application Firewall (WAF), and Intrusion Detection System (IDS), serve different purposes. A firewall controls network traffic based on an organization's security policy, a WAF protects web applications by filtering and monitoring HTTP traffic between a web app and the Internet, and an IDS monitors network traffic for suspicious activities and issues alerts when such activities are discovered.