Set external computer IP to environment variable

I have an external computer with an IP address like 100.12.5.7 and I would like to set a path to the environment variable like so:

setx MEDIA \\100.12.5.7\d\media\

When I tried the above command, cmd prompt me that the variable is set successfully but when I do an echo %MEDIA%, it only shows me %MEDIA% instead of the full path. Any idea how I could fix this?