Enterprise QoS Solution Reference Network Design Guide

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How Can I Use QoS Tools to Mitigate DoS/Worm Attacks? 1-28 Enterprise QoS Solution Reference Network Design Guide Chapter 1 Quality of Service Design Overview Worms have existed in one form or another since the beginning of the Internet, and have steadily increased in complexity and scope of damage, as shown in Figure 1-9. Figure 1-9 Business Security Threat Evolution Global Impact Regional Networks Multiple Networks Individual Networks Individual Computer 1st Gen Boot Viruses There has been an exponential increase since 2001 in not only the frequency of DoS/worm attacks, but also in their relative sophistication. For example, more than 994 new Win32 viruses and worms were documented in the first half of 2003, more than double the 445 documented in the first half of 2002. Some of these more recent worms are shown in Figure 1-10. Figure 1-10 Recent Internet Worms 2nd Gen Macro Viruses, Trojans, Email, Single Server DoS, Limited Targeted Hacking There are two main classes of DoS attacks: 3rd Gen Multi-Server, DoS, DDoS, Blended Threat (Worm+ Virus+ Trojan), Turbo Worms, Widespread System Hacking Next Gen Infrastructure Hacking, Flash Threats, Massive Worm Driven DDoS Negative payload Viruses, Worms and Trojans 1980’s 1990’s Today Future sadmind/IIS Code Red NIMDA May 2001 May 2001 Sept 2001 Sophistication of Threats Apache/ mod_ssl July 2002 MS-SQL Slammer W32/Blaster W32/Sobig W32/MyDoom W32/Bagel Spoofing attacks—The attacker pretends to provide a legitimate service, but provides false information to the requester (if any). Slamming/flooding attacks—The attacker exponentially generates and propagates traffic until service resources (servers and/or network infrastructure) are overwhelmed. Spoofing attacks are best addressed by authentication and encryption technologies. Slamming/flooding attacks, on the other hand, can be effectively mitigated through QoS technologies. Jan 2003 Aug 2003 Jan 2004 119478 April 29 2004 Sasser Version 3.3 119479
Chapter 1 Quality of Service Design Overview Version 3.3 How Can I Use QoS Tools to Mitigate DoS/Worm Attacks? Worms, on the other hand, exploit security vulnerabilities in their targets and disguisedly carry harmful payloads that usually include a self-propagating mechanism. Network infrastructure usually isn’t the direct target of a worm attack, but can become collateral damage as worms exponentially self-propagate. The rapidly multiplying volume of traffic flows eventually drowns the CPU/hardware resources of routers and switches in their paths, indirectly causing Denial of Service to legitimate traffic flows, as shown in Figure 1-11. Figure 1-11 Direct and Indirect Collateral Damage from DoS/Worm Attacks System under attack End systems overload High CPU Applications impacted Access Distribution A reactive approach to mitigating such attacks is to reverse-engineer the worm and set up intrusion detection mechanisms and/or ACLs and/or NBAR policies to limit its propagation. However, the increased sophistication and complexity of worms make them harder and harder to separate from legitimate traffic flows. This exacerbates the finite time lag between when a worm begins to propagate and when the following can take place: Sufficient analysis has been performed to understand how the worm operates and what its network characteristics are. An appropriate patch, plug or ACL is disseminated to network devices that may be in the path of worm; this task may be hampered by the attack itself, as network devices may become unreachable for administration during the attacks. These time lags may not seem long in absolute terms, such as in minutes, but the relative window of opportunity for damage is huge. For example, in 2003, the number of hosts infected with the Slammer worm (a Sapphire worm variant) doubled every 8.5 seconds on average, infecting over 75,000 hosts in just 11 minutes and performing scans of 55 million more hosts within the same time period. Note Interestingly, a 2002 CSI/FBI report stated that the majority of network attacks occur from within an organization, typically by disgruntled employees. This underscores the need to protect the Access-Edges of enterprise networks as well as their Internet edges. A proactive approach to mitigating DoS/worm flooding attacks within enterprise networks is to immediately respond to out-of-profile network behavior indicative of a DoS or worm attack using Campus Access-Layer policers. Such policers meter traffic rates received from endpoint devices and markdown excess traffic spikes to the Scavenger class (DSCP CS1) when these exceed specified watermarks (at which point they are no longer considered normal flows). Core Network links overload High packet loss Mission critical Applications impacted Routers overloaded High CPU Instability Loss of management Enterprise QoS Solution Reference Network Design Guide 119480 1-29
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