Which command would be used to display active connections and listening ports for TCP/UDP protocols?

The command that would be used to display active connections and listening ports for TCP/UDP protocols is 'ss'. This tool is specifically designed to investigate sockets, showing various statistics and details about network connections, both established and those in a listening state. It provides a more comprehensive view of connections compared to legacy commands, and it can filter output in a variety of ways, including by protocol type, making it particularly useful for network diagnostics and monitoring.

The other options serve different purposes: 'arp' manages the ARP cache for mapping IP addresses to MAC addresses; 'lsof' lists open files, which can include network socket information but is broader in scope; and 'ifconfig' is primarily intended for configuring network interfaces rather than displaying connection information. Therefore, 'ss' is the most suitable command for the stated requirement.