What type of attack is used to overload a specific protocol or service?

What type of attack is used to overload a specific protocol or service?

• Flood
• Back door
• Spoofing
• Man in the middle 

EXPLANATION

A Layer 7 HTTP Flood Attack is a type of DDoS attack made to overload specific parts of a site or server. They are complex and hard to detect because the sent requests look like legitimate traffic. These requests consume the server's resources causing the site to go down