port forwarding 15000 to internal 15000

Question

Try to set up port forwarding. Made a DNAT rule with forwarding http (external port 80) to port 15000 on internal server. That works! 
 Then changed the rule to forward external port 15000 to internal port 15000. Doesn't work! 
 Just changed the port. What is wrong?

MasterRoshi · Answer

This is either one of the ISP's blocking the higher range port or a configuration issue with the DNAT (specifically the service object source port). 
 Do you see the NAT rule being hit when you test with 15000? Turn on logging on the rule and check that.