SQL Server Used For Data Protection Manager Is Not Using A Default Port
During the install of Microsoft System Center Data Protection Manager 2010 (DPM) you can choose to use a an existing installation of SQL server used to host the DPM configuration database (rather than having DPM install local copy of the SQL dedicated just for DPM). When that SQL server is on a remote (remote to DPM server) box and runs on a standard TCP port (1433) there is no problem (assuming firewall rules allow connecting to that server on port 1433). However if the SQL server is configured to accept connection on a non-default (custom) TCP port (ex: TCP port 28321) then the Setup Wizard will fail even if you specify port number as part of a server name (ex: sqlserver1.domain.local,28321).
Instead what you need to do is go to Start select Run and type cliconfg.exe and press Enter. This will launch the SQL Server Client Network Utility which is part of Windows Server OS. You can use this utility to create an "Alias" (in the Alias tab) for the target SQL server and specify the non-standard port. Click on the Alias tab, then click Add. In the Server alias box on the top of the screen type the FQDN server name (ex: sqlserver1.domain.local) then select TCP/IP from the Network libraries section and uncheck the Dynamically determine port checkbox. In the Port number box type the custom SQL TCP port (ex: 23831) and hit OK, then Apply the changes.
Once you do so you will be able to simply enter the name used as the alias in the DPM Setup Wizard box when it is asking you for "Instance of SQL Server" name.