Denial-of-service or DoS attack is an attempt to make a machine or network resource unavailable to its intended users, such as to temporarily or indefinitely interrupt or suspend services of a host connected to the Internet.
DOS attackers make it impossible for network users to access information or services by flooding the network with requests that tie up its resources.
Single-origin DoS attacks can be effective against undefended victims, but they have a few key limitations:
1. Victims can block the originating IP address, either at the firewall level (to kill HTTP requests) or further upstream at the ISP level (to kill network-level floods).
2. Security tools now exist to detect and prevent ICMP flood attacks. Web servers can be configured to detect and block HTTP request attacks.
3. Enterprise products can identify and block single origin attacks as soon as they begin.
So these days attackers use DDoS, or Distributed Denial of Service attack -
Can a DDoS be stopped?
It is very difficult to defend against a sophisticated DDoS attack launched by a determined adversary.
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