New Denial of Service Attack on Panix

Tim Bass writes:

Thanks for pointing out that the UNREACHABLE could just
be hosts that are turned off. The difficult case,
now that you mention it, are the UNREACHABLEs due
to a route flap or other intermediate system blip.

A host being down is _not_ necessarily an UNREACHABLE host. In most
cases you won't see _anything at all_ if a host on an ethernet is down.
A smart router might detect a chronically unresolved ARP and produce an
ICMP_UNREACH, but do you know about routers like that?