North American Network Operators Group
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Re: Real-Time Mitigation of Denial of Service Attacks Now Available With AT&T

  • From: Danny McPherson
  • Date: Wed Jun 02 13:42:28 2004 
On Jun 2, 2004, at 10:56 AM, Richard A Steenbergen wrote:
What people may being seeing is that poorly randomized source attacks are
being automatically filtered by uRPF loose or other means before they ever
reach the target. I keep track of my network border filter counters, and
believe me spoofed attacks are not going out of style,
How do you discriminate *DDOS attacks employing source address spoofing*
from broken NATs, rampant worms, PMTU and other related misconfiguration
resulting in backscatter and similar garbage - with filter counters? Given,
tactically deployed filters in order to mitigate a specific attack to a particular
destination would likely glean some value WRT the validity of the source
distribution for a given attack, but not generally deployed filters for any
destination.

And exactly what represents "spoofed" by your definition? Note again that
I explicitly called out **DDOS attacks employing source address spoofing**,
which is non-inclusive of spoofing in general employed by worms and the
like, or common misconfigurations and brokenness that results in the slew
of random garbage floating about.

 especially from foreign and certain smaller networks.
I'd be extremely interested in any empirical evidence you have to support
this, and in better understanding exactly how you determined "foreign and
certain smaller networks" were indeed the source of many of these spoofed
packets.

As a customer of someone who does this kind of filtering and maintains
sufficient border capacity, you may never see the gigabits of src bogons,
protocol 0 or 255, port 0, 40 byte syns w/no MSS option, etc, and assume
that these attacks are out of style because the only ones that get through
are the WinXP MSS+SACK unforged drone SYNs.
I agree, if it's filtered before someone observes it, it won't be
observed :-)

However, distinguishing between coordinated DDOS attacks that employ source
address spoofing and "run of the mill" spoofing (by worms and the like) or
simple misconfiguration of some sort resulting in "backscatter" is key.

-danny