I was recently receiving a 'The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)' error message when attempting to configure the migration hierarchy for a SCCM 2007 to 2012 migration.
Checking back on the TechNet articles to confirm, the stated ports required for migration are:
These ports were open. I could establish a SQL connection but could not make the WMI connection.
On further investigation, WMI makes a call using port 135 but also uses a random port to connect. The following random ports are required to allow connectivity,
In Windows Server 2008 and later versions, and in Windows Vista and later versions, the default dynamic port range is:
Windows 2000, Windows XP and Windows Server 2003 use a dynamic port range of