When an analyst detects an unexpected change in network traffic, such as a significant increase in volume during odd hours, it is crucial to analyze the type of traffic to determine if the activity is benign or malicious. This initial step will guide subsequent investigative actions, such as activating intrusion detection systems or informing the incident response team. Checking for open ports that shouldn't be open would not immediately explain the traffic spike. Similarly, updating network device firmware is a maintenance task that is unlikely to directly address an ongoing traffic anomaly. Restricting outbound traffic would be a mitigation step once malicious activity is confirmed; this would potentially prevent data exfiltration but does not constitute an initial analysis of the situation.