Which of the following is a process of monitoring data packets that travel across a network?

ICMP (Internet Control Message Protocol) is a network-layer protocol used for sending error messages and operational information such as ping requests, not for monitoring or capturing packets.

SCP (Secure Copy Protocol) is a file transfer protocol that uses SSH encryption to securely copy files between hosts, not a method for observing network traffic.

A rootkit is a category of malicious software designed to gain unauthorized root-level access to a system and conceal its presence, not a network monitoring process.

Packet sniffing involves using software or hardware tools to intercept and log network traffic passing through a network interface, operating at the data link layer to capture raw packets for analysis. It is fundamental to network diagnostics and security monitoring, and can also be exploited by attackers to capture unencrypted sensitive data such as credentials. This makes it the precise technical term for monitoring data packets traveling across a network.