I have a new ArcServer 10.3.1 installation on a Windows 2012R2 server. I went through installing a new site and added user and admin ArcGIS server connections in ArcCatalog 10.3.1 on the server itself, and was able to preview the sample map service, SampleWorldCities. I thought I was on my way, but when I tried Add ArcGIS Server on a client Windows 10 PC with Desktop 10.3.1 ArcCatalog on a network without a domain to add a user connection, I couldn't seem to guess at the connection url. Tried http://servername:6080/arcgis/services, http://serverIP:6080/arcgis/services, http://NSMAP.Workgroupname.local:6080/arcgis/services and a few others, like putting /rest on the end, but they all failed. But in the first two forms, they took longer to fail, and got a message "We were unable to connect to:..... Error:Proxy server got bad address from remote server (verify the server is running).
But then I had an idea, Crap! Is this another Windows Firewall problem on the server? https://community.esri.com/thread/174271 I turned off the server's firewall private and public profile temporarily, and the client PC hooked up right away with http://servername:6080/arcgis/services.
What windows firewall settings do I need to change to fix this, and where the heck is the ESRI documentation on this stuff?