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