The number of TCP syn-ack amplifiers is large. It may suffice to allow clogging a provider or IX, using low load per amplifier, as described. Such low load is likely to be undetected by most operators, and even when detected (e.g. by Jim), only few (e.g. Mike) will have sufficient motivation to block it - esp. considering that there blocking it would often be non-trivial, in Mike's case, the amplifiers were DNS servers and sounds like he simply blocked packets to unallowed networks (good practice for DNS anyway - although I wonder why not block the incoming requests instead). Notice that one annoying aspect of these attacks is that tcp congestion control isn't relevant.
The current packets could be part of a research experiment about this threat, or the instrumentation part of preparing such attack. I would not rule out research, since it isn't trivial to know if the attack can be really viable to clog a provider or IX; in fact finding this out in an ethical way appears a non-trivial challenge, I'll give it some thought (ideas welcome). Also I wonder what would be good _defenses_ against such attack. Of course one way would be to prevent spoofed-IP packets, but that goal has proved quite difficult...
-- Amir Herzberg
Comcast professor for security innovation
Dept. of Computer Science and Engineering, University of Connecticut