Final answer:
Firewalls can be programmed to examine TCP headers, including the SYN flag, to control network traffic for security purposes; they are designed for this type of inspection, unlike network switches, routers, or load balancers.
Step-by-step explanation:
Devices that can be programmed to examine TCP headers to find the SYN flag are typically designed to monitor and control network traffic for security purposes. Among the options provided:
- Network switches generally operate at the data link layer (Layer 2) and are not typically responsible for inspecting TCP headers, which are at the transport layer (Layer 4).
- Routers can route traffic between different networks and sometimes offer some level of packet inspection, but they are not primarily used for inspecting TCP headers.
- Firewalls are specifically designed to inspect and filter traffic based on various criteria, including the examination of TCP headers and the SYN flag, to prevent unauthorized access or to monitor and control the flow of network traffic.
- Load balancers distribute traffic across multiple servers but do not typically inspect packet headers to control traffic like firewalls do.
Therefore, the correct answer is Firewalls (3).