The criminals behind denial-of-service (DoS) attacks usually go after the servers of credit card companies and banks. However, some are motivated by activism, revenge or blackmail, and so their targets can be ordinary people just going about their lives. During the past several years, the number and scale of DoS attacks have increased worldwide.

DoS vs. DDoS Attacks

A DoS (denial-of-service) attack is from one source and tries to make a network resource or machine unavailable to its users by interrupting or suspending the services of a host connected to the Internet.

A DDoS (distributed denial-of-service) attack comes from multiple sources, usually thousands of different IP addresses. Such attacks are like hundreds of people crowding a Walmart entrance before Black Friday, but they do not have any intention of entering. This prevents legitimate shoppers from going inside, causing a disruption of services.

Symptoms

According to the United States Computer Emergency Readiness Team (US-CERT), below are the symptoms of denial-of-service attacks:

• Unusually slow network performance (opening files or accessing websites).
• Unavailability of a particular website.
• Inability to access any website.
• Dramatic increase in the number of spam emails received (this type of DoS attack is considered an e-mail bomb).
• Disconnection of a wireless or wired internet connection.
• Long-term denial of access to the web or any internet services.

Mitigation

US-CERT also states, “Unfortunately, there are no effective ways to prevent being the victim of a DoS or DDoS attack.” However, over time experts have determined methods to mitigate their effects. They use a multi-layered approach for large companies as listed below.

• Automated Mitigation – DDoS mitigation tools filter out noise and pass clean traffic further into the network.
• Bandwidth Oversubscription: Overcapacity of servers helps make attacks ineffective.
• System Hardening – Operating systems and applications configured for more resiliency during application layer DDoS attacks.
• Third Party Provider – DNS-based redirect or BGP-based services are deployed in the event of sustained attacks. CDNs can offer similar protection, which would be applicable for smaller businesses because of affordability.

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