BSDCon 2002 Abstract
Resisting SYN flood DoS attacks with a SYN cache
Jonathan Lemon, FreeBSD Project
Machines that provide TCP services are often susceptible to various
types of Denial of Service attacks from external hosts on the network.
One particular type of attack is known as a SYN flood, where external
hosts attempt to overwhelm the server machine by sending a constant stream
of TCP connection requests, forcing the server to allocate resources
for each new connection until all resources are exhausted. This paper
discusses several approaches for dealing with the exhaustion problem,
including SYN caches and SYN cookies. The advantages and drawbacks of
each approach are presented, and the implementation of the specific
solution used in FreeBSD is analyzed.
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