UDP_port_issue.txt

"Qport was added to the NetChannel header to fix a bug. Before the qport, Quake server identified a client by the combination (remote IP,remote UDP port). This worked fine most of the time but certain NAT router can change their schema of port translation (remote UDP port) sporadically. UDP port being unreliable, John Carmack explained in one of his plans that he decided to identify a client by (remote IP, Qport in NetChannel header). This fixed the confusion and also allowed the server to adjust the target UDP response port on the fly." - http://fabiensanglard.net/quakeSource/quakeSourceNetWork.php