DOS (Denial of service) is an attack on computers or networks that restricts or prevents legitimate use. In a DOS attack, an attacker uses a flood of packets to slow down or crash the target system or an entire network.
Computers have limited resources, for example computation power or memory. When these are exhausted, the program can freeze or crash, making it unavailable. A DOS attack consists of various techniques to exhaust these resources and make a server or a network unavailable to legitimate users.
Types of DOS attack
DOS attacks are more of a category than a particular kind of attack. Here is a non-exhaustive list of DOS attack types:
- bandwidth attack
- service request flood
- SYN flooding attack
- ICMP flood attack
- peer-to-peer attack
- permanent DOS attack
- application level flood attack
Symptoms of DOS attack
When a server is under a DOS attack, users may experience sluggish network performance, or have trouble accessing some or all websites.