I've been following the discussion on DDoS attacks over the last few weeks
and our network has also recently been the target of a sustained DDoS
attack. I'm not alone in believing that source address filters are the
simplest way to prevent the types of DDoS traffic that we have all been
seeing with increasing regularity. Reading the comments on this list have
lead me to believe that there is a lot of inertia involved in applying
what appears to me as very simple filters.
As with the smurf attacks a few years ago, best practice documents and
RFC's don't appear to be effective.
BCP 38 is quite explicit in the need for all networks to do their part. The document is quite effective provided there's cooperation.
I realise that configuring and
applying a source address filter is trivial, but not enough network admins
seem to be taking the time to lock this down. If the equipment had
sensible defaults (with the option to bypass them if required), then
perhaps this would be less of an issue.
Therefore, would it be a reasonable suggestion to ask router vendors to
source address filtering in as an option on the interface and then move
it to being the default setting after a period of time? This appeared
to have some success with reducing the number of networks that forwarded
broadcast packets (as with "no ip directed-broadcast").
So you're suggesting the router vendors provide default configurations which the ISPs will overwrite with their current configurations anyway? Which interface would you filter on? If we're talking about a router at the customer premesis, the filters should be on the link to the ISP (the customer may well have more subnets internally). At the ISP end, doing the filtering you suggest would not work, since it'd permit only the IP addresses of the link between the customer and user.
For dialups, such filtering can and should be done, and should be automatic in the NAS boxes.
But the #1 question I have to ask you is, how are you going to have any more luck enforcing ingress filtering with what you propose, than what we have in the BCP on the subject?
If the government or other large buyers require network-wide ingress filtering in any supplier they buy from (something I suggested to the folks at eBay, Schwab, etc. in our phone calls after the attacks a few years ago), or if there were legal incentive, there might be a chance ISPs would find a financial motive to implement BCP 38. As it is, there's no incentive, so the path of least resistance is to do nothing.