Which device can inspect packets at the application layer to identify potential security threats?

A firewall is specifically designed to inspect packets at the application layer, which enables it to analyze the content and context of data packets beyond just their headers. This deep packet inspection capability allows firewalls to identify potential security threats such as intrusions, malware, or malicious activity by examining the actual data being transmitted and determining whether it complies with defined security policies.

Firewalls can employ a variety of techniques, including signature-based detection where known threats are identified, as well as anomaly-based detection where the behavior of the traffic is analyzed to spot deviations from normal patterns. By operating at the application layer, a firewall provides a higher level of scrutiny compared to devices like routers or switches, which primarily focus on directing traffic based on IP addresses and forwarding frames without interpreting the data payload.

Devices like routers and switches do not have the capability to perform this level of inspection, as they function primarily at the network or data link layers. A modem, on the other hand, primarily serves to modulate and demodulate signals for communication over phone lines or cable, without inspecting packet content at any layer. Thus, a firewall stands out as the essential device for application layer packet inspection and security threat identification.