Denial of Service

Question 1

Denial of service

Answer 1

• Force a service to fail
  
  • Overload the service
• Take advantage of a design failure or vulnerability
  
  • Keep your systems patched!
• Cause a system to be unavailable
  
  • Competitive advantage
• Create a smokescreen for some other exploit
  
  • Precursor to a DNS spoofing attack

• Doesn’t have to be complicated - Turn off the power

Question 2

A “friendly” DoS

Answer 2

• Unintentional DoSing - It’s not always a ne’er-do-well
• Network DoS - Layer 2 loop without STP

• Bandwidth DoS
• Downloading multi-gigabyte Linux distributions
over a DSL line

• The water line breaks - Get a good shop vacuum

Question 3

Distributed Denial of Service (DDoS)

Answer 3

• Launch an army of computers to bring down a service
  
  • Use all the bandwidth or resources - traffic spike

• This is why the bad guys have botnets
• Thousands or millions of computers at your
command
• At its peak, Zeus botnet infected over 3.6 million
PCs
• Coordinated attack

• Asymmetric threat
• The attacker may have fewer resources than the
victim

Question 4

DDOS amplification

Answer 4

• Turn your small attack into a big attack
  
  • Often reflected off another device or service
• An increasingly common DDoS technique
  
  • Turn Internet services against the victim

• Uses protocols with little (if any) authentication or
checks
• NTP, DNS, ICMP
• A common example of protocol abuse