Karl Denninger writes...
Then you damn well better not be permitting any of the following:
1) Forged source addresses (this CAN be stopped with specific filters on your interfaces, although some will bitch about the performance impact - depending on their specific choices)
Yet another case for pressing (now) ARIN (and others who allocate address space) to do address allocation in reasonable chunk sizes instead of forcing providers to accept little bits of address space a piece at a time. Prefix volume on BGP would be helped, too, by having fewer little pieces scattered all around. And with address space now on a paid basis, in theory people will generally ask for what they expect to need (there will be exceptions but they should be easy to spot), so there is more reason to actually give out requested allocations that are not obviously inflated.
2) Directed broadcasts (which are used to "create" these DOS attacks by bouncing the attack off a particularly-well-connected location, USUALLY a provider's internal infrastructure).
Block both of those and Smurfs would disappear. If you can trace the TRUE source of such an attack quickly, people will go to jail for this. The only reason they are popular is because the source addresses CAN be forged.
Specific information is always helpful. Unfortunately, if it has been given on NANOG, it can be missed due to the high noise level (yet another issue we need to work on). Would config examples in IOS and gated be too much to ask for (if someone only knows one, someone who knows the other should follow up).
THIS CAN BE PREVENTED.
Agreed. Let's make it easy. -- Phil Howard | die3spam@spammer3.org eat4this@dumb3ads.edu no1way94@dumbads5.org phil | no0way53@no9where.edu end9ads2@noplace0.org stop9361@dumb4ads.org at | no7spam1@spammer8.org die2spam@no5place.edu blow2me0@no39ads6.edu milepost | stop3it3@lame2ads.com w2x4y9z8@lame1ads.edu eat2this@noplace1.net dot | no14ads6@nowhere0.org no6spam1@spam8mer.com no5way06@nowhere3.net com | die6spam@no66ads9.com stop5758@no39ads5.org eat1this@anywhere.org