Re: [DNSOP] [Ext] the power of ideas

Edward Lewis <> Tue, 04 April 2017 15:30 UTC

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From: Edward Lewis <>
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Thread-Topic: [Ext] [DNSOP] the power of ideas
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Date: Tue, 04 Apr 2017 15:30:06 +0000
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Subject: Re: [DNSOP] [Ext] the power of ideas
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On 4/3/17, 16:00, "DNSOP on behalf of Paul Vixie" < on behalf of> wrote:

    On Monday, April 3, 2017 7:48:49 PM GMT Paul Wouters wrote:
    > ...
    > As Evan said, there should not be any code in an authoritative server
    > that requires it to do recursive validation.
I'm going to squat on Paul Vixie's subject line but not respond to anything he says, in part because something crossed my mind, based, ironically enough, in a conversation Paul and I had not long ago (at an ICANN meeting venue).

We reminisced about client-subnet-id.  There was a way-back time when I spoke of a q-trinity - qname, qtype, qclass - being the three things needed to get a specific response from DNS.  Including any other information was a pollutant.

Paul pulled that out when my name was on an early version of the client-subnet-id document (as a caretaker editor).  The reason I was participating in that was seeing how the implementation of "stupid DNS tricks" (as one side of the war might call them) or "tailored DNS responses" (as the other side of the war might call the same battle) got carried out in specific contexts.  They "worked" despite some flaws and dire predictions.

It isn't that it's a sin to pollute the query with other information, there's a cost of doing so.  In some cases, the cost is worth the benefit, in others, not.  It's not a binary "do it or not" but a sliding scale of "is the cost less than the benefit?" I say sliding because "cost" and "benefit" are not fixed values over time.  (Moore's law, Kaminsky's BlackHat presentation change cost and benefit calculations.)

Back to the quote above.  In general, an authority server having to do lookups will have scaling implications, suck performance, present a potential for abusive loading (think DoS/DDoS).  (Related but different, DNSSEC once required the server verify signatures on load - that slowed loading zones, so it was dropped with the consequence of having to carefully define the AD bit in a response.)  But in specific, managed and contained contexts, having authorities look up data to improve an answer can be worth the cost.

Question hard-and-fast rules from the past.  Things change.