STATS u

Usage: STATS u [<server>]
Usage: STATS U [<server>]
Uptime: u - Shows how long the server has been running.
Unknown connections: U - See the IP addresses of the unknown connections to your server. Connections can be open for a variety of reasons. Most common is that the client is waiting for DNS resolving to happen. You can close these connections with the CLOSE command.
Examples:
/stats u
/stats u arena.*
/stats U
/stats U arena.*