Irrelevant links in 2017 are the real 'villains' in your digital marketing strategy. You are better off forgetting about link networks, comment spam and other (black hat) techniques which put Google centre stage, instead of the user.
Whereas external back links used to be collected and immediately resulted in a top 5 position, this is now punished by means of a 'real-time' Google penalty. This can then lead to a huge loss in turnover. Luckily, since the Google penguin-update 4.0 this has worked in 2 directions and you can quickly recoup your page position by eliminating these links.