When you have more than one instance of SSAS installed in your Server you might end up in a situation to find the port numbers for each instance to set the firewall settings on the server. As you might all know the default Port for SSAS is TCP 2383,
To find the port number of the other instances search for the msmdredir.ini file on your ProgramFiles(X86)->Microsoft SQL Server folder, most probably the file resides in the (%ProgramFiles(X86)%\Microsoft SQL Server\90\Shared\ASConfig\msmdredir.ini)location, Look in both 64 bit and 32 bit Program Files folder but more likely to be in 32 bit folder even for 64 bit installations.
If you have more than 1 Instance you will have entry in the ini file like below, If you change the port number to 0 it would take dynamic ports else you can assign a static port to the instance.
The Above exercise will hold good only for Non-Clustered SSAS instance, Clustered SSAS instance always uses TCP Port 2383 with the corresponding SSAS Cluster Resouce IP.