We have a 2-node SQL 2005 cluster which hosts two (named) instances at the same time. In SQL Server Configuration Manager, there is an IP addresses list for TCP/IP protocol for each DB instance under SQL Server 2005 Network Configuration tab. I noticed that the IP of that specific instance does not exist in the list. However, it is correctly set by cluster admin and can be seen via ipconfig, netstat etc. What would be the reason? The default setting for DB instances to listen on dynamic ports. I changed the configuration to listen to static ports. The strange thing is that, although the IP of that instance is not in the list and therefore cannot be changed, it still works correctly, i.e. it listens to the static port although it was listening on dynamic ports before I changed the setting for other IPs. How can this be? Another strange thing is that for one instance its IP is not listed at all and for the other instance, the IP is in the list of the other instance. Some stranger thing is that this behavior repeats itself for a totally different cluster which has the same characteristics, i.e. two-nodes, two instances. Everything works fine now, but I do not how this happens. Does anybody have an idea how such?