DoS protection for UDP-based protocols

ABSTRACT

Since IP packet reassembly requires resources, a denial of service attack can be mounted by swamping a receiver with IP fragments. In this paper we argue how this attack need not affect protocols that do not rely on IP fragmentation, and argue how most protocols, e.g., those that run on top of TCP, can avoid the need for fragmentation. However, protocols such as IPsec's IKE protocol, which both runs on top of UDP and requires sending large packets, depend on IP packet reassembly. Photuris, an early proposal for IKE, introduced the concept of a stateless cookie, intended for DoS protection. However, the stateless cookie mechanism cannot protect against a DoS attack unless the receiver can successfully receive the cookie, which it will not be able to do if reassembly resources are exhausted. Thus, without additional design and/or implementation defenses, an attacker can successfully, through a fragmentation attack, prevent legitimate IKE handshakes from completing. Defense against this attack requires both protocol design and implementation defenses. The IKEv2 protocol was designed to make it easy to design a defensive implementation. This paper explains the defense strategy designed into the IKEv2 protocol, along with the additional needed implementation mechanisms. It also describes and contrasts several other potential strategies that could work for similar UDP-based protocols.

REFERENCES

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INDEX TERMS

Primary Classification:
  C. Computer Systems Organization
  C.2 COMPUTER-COMMUNICATION NETWORKS
      C.2.0 General
          Subjects: Security and protection (e.g., firewalls)

General Terms:
Algorithms, Design, Performance, Reliability, Security

Keywords:
DoS, IKE, IPsec, buffer exhaustion, denial of service, fragmentation, network security, protocol design