Re: [DNSOP] EDNS0 clientID is a wider-internet question

Christopher Morrow <> Tue, 25 July 2017 13:53 UTC

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From: Christopher Morrow <>
Date: Tue, 25 Jul 2017 09:53:18 -0400
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To: Ted Lemon <>
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Subject: Re: [DNSOP] EDNS0 clientID is a wider-internet question
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On Tue, Jul 25, 2017 at 5:55 AM, Ted Lemon <> wrote:

> On Jul 24, 2017, at 8:59 PM, Christopher Morrow <>
> wrote:
> and at the cache->auth layer it's potentially the case that the provider
> can say: "use precision of /24" or "use precision of /17" ? So, there's
> really not much "pii" that can be worried over at the
> provider-cache-resolver (they already know who you are...) and they
> (provider) can decide how much granularity is "important" to release to the
> upstream authoritative cache.
> There is no such thing as an upstream authoritative cache.   The filtering
> is being

apologies, 'upstream (from the cache resolver's perspective) authoritative

> done at the cache.   This is not client subnet: this is client ID.   So
> the cache, which is not authoritative, is receiving PII about a specific
> client machine.   Being able to

I agree with this, the cache resolver sees the client's IP address.

> filter the PII at the CPE would indeed improve privacy in this case; the
> problem is that the CPE has to have a UI or API that allows that to happen,
> and they don't.
I don't think the CPE is the answer, the cache-resolver CAN decide to send
along in it's edns0 option: "" instead of "". Or it
seems to me that this is a fine knob to add to resolver software... granted
you'd need some extra config about your client subnets in use.

> The reason DNS filtering is useful is not that it is forced upon the end
> user, but that it allows devices that use the default cache to get
> filtering in a way that does not

I don't believe the goal of the draft is to enable filtering.
Certainly for a nation-state actor you could see: "Oh, now I know what
subnets use the resolver over there, so I can limit useful replies, or
steer requestors toward 'better/approved' content'

> depend on the software installed on them.   So e.g. your IoT device can be
> infected by a worm but not actually exfiltrate any private information to
> the attacker, because the attacker's DNS is blocked.
you seem to be conflating a few things here... or using 'content filtering'
in a different way here than before in this response.

> Being able to know that a particular device is a particular device is
> actually quite useful in this context; unfortunately, there is no way to
> distinguish "useful" and "personally-identifying".   Even if you only
> identify the IoT devices in your home, by doing so you reduce the search
> space for identifying the other devices.
I don't think the draft is aiming at 'device' as much as 'region of the
network'. The cache resovler COULD choose to send /32 (or /128) level data
in the edns0 option, but that seems counterproductive, and a bit invasive.