Smurfable Networks

I don't see a single entry in that list which is a broadcast. I would say
someone is being taken here. Perhaps you were flooded with straight spoofed
echo replies, as most of these networks seem to be the EXTRA-responsible

Actually, it turns out that a some of what I posted were only echo replies
from single hosts. This was indeed a real one point we were
pulling about 50 Meg over 3 T3s. The error I made was in generating the
list of amplifier networks from my log files. Networks with even one
single echo reply to the target address were included in the list. Such
was the case with the net 12 entries - each one corresponded only to one
IP address, not a whole network worth.