Port :550new-rwho / new-who

UDP port 550 has historically been designated for the 'new-rwho' and 'new-who' services, which are successors to the original 'rwho' protocol. These services allow the broadcasting and collection of user login status information across networked UNIX systems, enabling administrators to track active sessions remotely. The protocol generally works by periodically sending updates to listening hosts, which compile these records into accessible lists of who is logged on where.

In operation, 'new-rwho' provides more efficient data handling and reduced network usage compared to its predecessor, with optimized broadcast mechanisms. It typically employs simple UDP datagrams to convey status data without any encryption or complex negotiation, prioritizing low overhead and simplicity. This design fits the trusted internal network model of its era, assuming minimal threat from internal actors.

While not widely used today due to privacy concerns and alternate, more secure user management tools, some legacy systems or controlled lab environments may still deploy 'new-rwho' and 'new-who'. Their lightweight nature and ease of setup mean occasional usage persists primarily for educational or compatibility reasons rather than mainstream administration tasks.