ephemeral port

The source port the kernel picks for an outgoing connection, taken from the range in net.ipv4.ip_local_port_range — 32768 60999 on Ubuntu 24.04. It exists because a TCP connection is identified by five values: the protocol, the source address and port, the destination address and port. Ten thousand clients hold connections to port 443 of one server at the same time because each brings a different source pair. The five-digit ports on one side of every ss -tn line are these: ephemeral ports doing their job, not mystery services to hunt down. The from 192.168.1.24 port 51624 in curl -v output is your own. A client end never has anything to open: an outgoing connection needs no listening socket.