Preventing a particular type of nameserver abuse

Mark Andrews marka at
Thu Apr 15 02:44:30 UTC 2021

> On 15 Apr 2021, at 11:35, @lbutlr <kremels at> wrote:
> On 14 Apr 2021, at 01:48, Anand Buddhdev <anandb at> wrote:
>> This is a short-sighted opinion. If just one authoritative server sends
>> out REFUSED responses towards an innocent, it won't matter. But if 1000
>> authoritative servers all send out REFUSED responses towards an innocent
>> IP address, their combined volume and packet rate *is* significant.
> Is it?
> How big is a REFUSED response?

Approximately the same size as the request.  It depends on the request and
the server’s capabilities.

> Even if it is 100 bytes (and I think it is not that large, but I cannot find it), 1000 refused would be 100K.
> How many thoudanss of servers do you need in this "DDoS" to overwhelm a pretty average connection? (My home connection is only 200Mbps down).
> Granted, a million machines would be generating a 100MB of data, which is insignificantes, but the number of pockets at that scale would probably be an issue. But is a million servers realistic?
> I don't think calling this a DDoS is accurate. It is more likely;y there is a known exploit for some servers and they are probing or it is some script kiddie just blasting out packets hoping to get lucky.

If you really want to do something, talk to your local politician and get laws written up that require ISPs to deploy BCP38.  This is completely fixable if ISPs deploy BCP38 filters on themselves and all of their customers.  There is some CAPEX and OPEX to deploying BCP38 filters and making it a requirement under law levels the playing field between ISPs.

> -- 
> "Are you pondering what I'm pondering?"
> "I think so, Mr. Brain, but if the sun'll come out tomorrow, what's
> 	it doing right now?"
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Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka at

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