Ban, slowdown or stop massive login attempts to RDP

Remote session from client name a exceeded the maximum allowed failed logon attempts. The session was forcibly terminated.

One of the servers are being hit by a dictionary attack. I have all the standard security in place (renamed Administrator, etc.) but want to know is there a way to limit or ban the attack.

Edit: The server is remote only. I need RDP to access it.

Block RDP at the firewall. I don't know why so many people allow this. If you need to RDP to your server, setup a VPN.

Change the port and virtually all attacks will stop.

Attacks are usually not directed to you specifically but to all IPs. So they won't try non-default ports because it's simply not worth it; trying the next IP has chances orders of magnitude greater than trying the next port.