Problem: We have faced an issue in production server in one of our client.There are three AOS server in NLB cluster. Server: AOS1,AOS2,AOS3 AOS1 is the primary AOS and other two are secondary.We have a practice when we deploy any fixes in production server then we stop AOS2 and AOS3 service and restart AOS1 service to drain user session from the AOS. Last time we try to restart the AOS1 service got error in event viewer and other two AOS service worked properly. "The Dynamics Server could not be started because TCP Port 2712 is already in use AX 2012" We have found some commands in google to check the port availability in AOS1 server but after running those command result were same. Solution: We just restart the AOS1 server .It took one minute to restart the machine and reset all the configuration and assign default 2712 port to AOS1 and server were running successfully.