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Network Defenses to Denial of Service Attacks

Network Defenses to Denial of Service Attacks. John Kristoff jtk@depaul.edu +01 312 362-5878. DoS attack prevention is difficult. Applications, hosts and networks are often significantly oversubscribed. Internet (data) traffic is naturally bursty on all time scales, thus

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Network Defenses to Denial of Service Attacks

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  1. Network Defenses to Denial of Service Attacks • John Kristoff • jtk@depaul.edu • +01 312 362-5878

  2. DoS attack prevention is difficult • Applications, hosts and networks are often significantly oversubscribed. • Internet (data) traffic is naturally bursty on all time scales, thus • discerning bad traffic from good can be hard. • There is no one, easy thing to fix that will make the problem go away. Its been proposed that re-architecting the Internet is a solution, but no one wants to go through that pain.

  3. Visualizing DoS Attack Data

  4. Visualizing Bottlenecks

  5. What are the popular defenses? • Block bogon, invalid and attack packets. • Monitor traffic thresholds, patterns and trends. • Rate limit traffic to help prevent oversubscription. • Prevent end hosts from becoming DoS agents. • Black hole victim hosts/networks. • Maintain good incident response and support staff. As you might guess, no one defense solves it all.*

  6. In depth look at packet blocking • Blocking invalid/bogon packets from reaching the net is generally considered a best practice. • However, it may severely impact forwarding performance and be difficult to manage. • Blocking on general attack characteristics may also block and break legitimate applications. Many ISPs mitigated the recent Slammer/Sapphire worm by temporarily blocking UDP port 1434 traffic.

  7. Traceback • Enabled routers generate or encode trace information to the traced destination. • Victims can use trace information to discover the real path back to the original source. • Authentication, deployment and practical issues exist.

  8. Source path isolation engine • Routers keep a hash of all packets passing through and send to a collector. • To trace a packet, query the collector based on packet characteristics. • SPIE can potentially trace a single packet. • Significant scaling and deployment issues.

  9. Pushback • A mechanism to signal downstream routers to aggressively drop/limit attack traffic. • Routers must detect attack traffic. A similar problem shared by signature based filters. • If attack traffic is widely distributed, pushback may be ineffective. IMHO, pushback and related techniques are the most interesting and elegant network-based solutions.

  10. Slammer/Sapphire the DoS attack

  11. Other defenses • Legal action. Costly (in more ways than one) and problematic when crossing legislative borders. • Mirror and distribute victims. Costly and management intensive. • User education? Security Forum 2003! Thanks! Stop by for a visit at http://ntg.depaul.edu/rd/

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