  Denial of service (DoS) and Distributed Denial of Service (DDoS) attacks
continue to threaten the reliability of networking systems. Previous approaches
for protecting networks from DoS attacks are reactive in that they wait for an
attack to be launched before taking appropriate measures to protect the
network. This leaves the door open for other attacks that use more
sophisticated methods to mask their traffic. A secure overlay services (SOS)
architecture has been proposed to provide reliable communication between
clients and a target under DoS attacks. The SOS architecture employs a set of
overlay nodes arranged in three hierarchical layers that controls access to the
target. We propose an architecture called secure overlay services (SOS) that
proactively prevents denial of service (DoS) attacks, which works toward
supporting emergency services, or similar types of communication. The
architecture uses a combination of secure overlay tunneling, routing via
consistent hashing, and filtering. We reduce the probability of successful
attacks by: 1) performing intensive filtering near protected network edges,
pushing the attack point into the core of the network, where high-speed routers
can handle the volume of attack traffic and 2) introducing randomness and
anonymity into the forwarding architecture, making it difficult for an attacker
to target nodes along the path to a specific SOSprotected destination. Using
simple analytical models, we evaluate the likelihood that an attacker can
successfully launch a DoS attack against an SOS protected network. Our analysis
demonstrates that such an architecture reduces the likelihood of a successful
attack to minuscule levels.
