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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: no ip forged-source-address
At 10:44 AM 10/30/2002, [email protected] wrote: BCP 38 is quite explicit in the need for all networks to do their part. The document is quite effective provided there's cooperation.Hi, 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. 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.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[1] on the interface and then move it to being the default setting[2] 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"). 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.
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