Network programming inside the View Controller... bad practice?

Quite a broad quesiton, I know.

Is it bad practice to keep networking in the View Controller, outside of the model? Or would this be preferred in the model? E.g. currently have a ViewController where I fetch JSON data via. a URL request, parse it, and present it to the view.

I use the data of the JSON result as attributes in an object of my data model. Bad practice?

I'm specifically working with iOS right now, but anything is okay for me, I'm just trying to understand.