What could be the cause for clients on the network contacting the same external IP address every five minutes?

Clients on the network consistently contacting the same external IP address every five minutes is indicative of a repetitive external connection, which can often be a sign of malware infection. Malware is designed to establish communications with command and control servers or to exfiltrate data. In many cases, this occurs at regular intervals, allowing the malware to receive instructions or send stolen information back to its source.

When considering the nature of malware, it's common for certain types (like trojans or bots) to reach out to a predetermined IP address on a repeated basis. This behavior could be orchestrated by the malware's programmatic design to maintain communication with the attacker or to enable remote control of the infected machine.

Scheduled updates usually occur at specific intervals determined by software or system settings but wouldn't typically result in repeated communication with the same external IP address unless configured to do so in a specific manner. Configuration issues and network misconfiguration can lead to abnormal network behavior, but they would not specifically cause all clients to consistently contact the same external IP address on such a frequent and regular basis.