IANA reserves 9011/tcp and assigns 9011/udp to amateur-radio D-Star routing.
The registry marks 9011/tcp as Reserved — deliberately held back, not available for assignment — while 9011/udp is d-star, "D-Star Routing digital voice+data for amateur radio". So the interesting traffic on this number is UDP and belongs to ham radio gateways. A TCP listener on 9011 is therefore something local and unregistered; find the process.
Expose with care
For a D-Star gateway the UDP side is meant to reach other gateways; a TCP listener here is unexplained until you identify it.
$ sudo lsof -nP -iTCP:9011 -sTCP:LISTENSeen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
Get Beige Box →also available as JSON · Markdown
Corrections or a missing port? Reply @rimrocksystems.