Do I need domain mapping plugin still

I have read that domain mapping comes as default with WP. Does that mean it is the plugin comes as default? Or is it integrated?
Because I still have activate the plugin and it is already giving error for my network not being on the root. My network is installed in a folder.
If it comes as default and folder installation is acceptable, why do I get an error?
Do I still need to do a manual installation to overcome that error?