Block ip adress (Server 2012 R2, IIS 8.5)

I getsome strangeattacksfrom differentIPaddresses.

Whichis the bestway to limit access to thoseIPaddresses?

Is it betterthrough therouter to block?

Atthe serverlevel or throughIIS?

Please provideanswersonly those who understand thesubject matter, what's the bestway to blocktheseIPaddresses, and how?

Thank you.

Server 2012 R2, IIS 8.5