[ratelimits] Remarks regarding the Knot DNS 1.2.0 RRL implementation

Paul Vixie paul at redbarn.org
Wed Mar 6 04:36:24 UTC 2013

can afilias and nominet please jump in here? we've already heard from icann.

Marek Vavruša wrote:
>> i think we're in disagreement. if someone using OSPF ECMP to
>> front-loadbalance a brace of DNS servers, one third of which run BIND9, one
>> third run Knot, and one third run NSD; if an attack comes which registers as
>> a certain response profile -- that is, what is omitted and what is not
>> omitted; if one of the servers is taken down for maintainance and is thus
>> removed from the ECMP set; then the response profile should not change, even
>> though there will be a new ECMP hash directing 4-tuple flows toward the
>> remaining ECMP brace members. that's a nightmare for operators. we do not
>> need to wait for them to experience it and tell us that we should not have
>> coded it that way.
> Can't tell. To be honest, I don't have much experience as an operator.
> Could we have more people to chime in?

yes, please. ops people, please indicate your desires here, even if it's
just to +1 what jabley already said.

>> if the tech-note is inadequate in its description of the mapping from tuple
>> to bucket, please propose more exact wording.
> So, should we store complete qnames in the tuples or should we accept false positives?

in bind9 there's a 32 bit hash of the qname in each chained bucket.
that's a far larger collision domain than you'll see in an unchained
hashing scheme. so my answer to your question is: "it depends on the
size of the collision domain".

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