A new paper on reacting to (distributed) denial of service attacks, published by Micah Adler of UMass-Amherst on October 2. Worth reading; some very clever ideas are emerging on this subject.

"There has been considerable recent interest in probabilistic packet marking schemes for the problem of tracing a sequence of network packets back to an anonymous source. [...] In this paper, we introduce a new marking technique for tracing a sequence of packets sent along the same path. [...] the sequence of packets can be traced back to their source using only a single bit in the packet header. [...]"

Tradeoffs in Probabilistic Packet Marking for IP Traceback