Re: [DNSOP] Fundamental ANAME problems

Lanlan Pan <> Sat, 03 November 2018 12:44 UTC

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From: Lanlan Pan <>
Date: Sat, 03 Nov 2018 08:42:43 -0400
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To: Brian Dickson <>
Cc: John Levine <>, " WG" <>
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Subject: Re: [DNSOP] Fundamental ANAME problems
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Brian Dickson <>于2018年11月2日周五 上午9:38写道:

> On Thu, Nov 1, 2018 at 5:14 PM John Levine <> wrote:
>> I can't help but note that people all over the Internet do various
>> flavors of ANAME now, and the DNS hasn't fallen over.  Let us not make
>> the same mistake we did with NAT, and pretend that since we can't find
>> an elegant way to do it, we can put our fingers in our ears and it
>> will go away.
> Did you not read my full message?
> I didn't say don't do that, I said let's do it in an elegant way.
> Then I provided a few examples of how to do that.
> What is being done now is not ANAME by any stretch; it is
> vertically-integrated apex CNAME flattening.
> Yes, there are several providers doing it.
> Their customers are locked in to a single provider, precisely because of
> that vertical integration.
> None of their customers can have multi-vendor redundancy with feature
> parity.
> While not a prime motivation for ANAME or its alternatives, it is
> certainly (or should be) one of its goals.
> The fact that each existing vendor's solution is, and requires, vertical
> integration, means each is fundamentally a closed system, with no interop
> possible.
> What ANAME, and the other suggested things, are doing is figuring out how
> to do interoperable stuff that allows something kind of like a CNAME, to
> co-exist at an apex.
> Can you point me to a non-closed, non-vertically-integrated ANAME-like
> thing that offers interoperable multi-vendor support?
> I think you are confusing "dynamic update of A based on
> meta-data-configured FQDN" with actual ANAME.
> So, DNS not having fallen over yet, has nothing at all to do with ANAME.
>> In article <
>>> you
>> write:
>> >The requirement on update rate, is imposed externally by whichever entity
>> >operates the ANAME target. In other words, this is not under the direct
>> >control of the zone operator, and is potentially a potentially (and very
>> >likely) UNBOUNDED operational impact/cost.
>> "Something very bad will happen if I do that."  "OK, so don't do
>> that."  My aname-ish code has a maximum update rate, and I expect
>> everyone else's does too.  Yeah, the ANAMEs won't be in sync with
>> the hostile remote server, but I can't get too upset about that.
> How many zones do you operate this way?
> What is the maximum update rate?
> Are those zones you operate on behalf of paying customers?
> If those were paying customers, and the records got out of sync, don't you
> think the customers would get upset?
> That's the primary point; when non-toy situations with paying customers
> are considered, it isn't up to you to decide what the update rate is, and
> you don't have the luxury of not caring.
> It isn't whether it works for you; it's whether it works for EVERYBODY.
> If it doesn't, then we need to work harder on the problem.
>> >Third, there is an issue with the impact to anycast operation of zones
>> with
>> >ANAMEs, with respect to differentiated answers, based on topological
>> >locations of anycast instances.
>> How is this different from CNAMEs via to and other anycast
>> caches?  The cache has no relation to the location of the client unless
>> you use one of the client location hint hacks.
> Because authority servers for the same zone, when not doing stupid DNS
> tricks, are in sync.
> This is by design, and is the expectation of clients, resolvers, and
> registrants.
> Anycast caches do not have any expectation or requirement to be sync'd,
> and in particular, due to stupid DNS tricks, are typically topologically
> sync'd to regional answers.
> Anycast caches with smaller footprint or odd customer bases, might do
> those hacks, but even without them, there will be significant differences
> in the contents of those caches, in different locations.
> The problem is the ANAME *target* -- that will typically also be
> topologically diverse, e.g. answers supplied will involve stupid DNS tricks.
> You can't have your ANAME use only a single view and push that SAME answer
> to all anycast nodes.
> Doing so would break the client->resolver->(anycast auth)->ANAME-target
> model of diversified answers.
> If client/resolver are supposed to hit ANAME-targets (which are themselves
> anycast, but which do stupid DNS tricks to give different answers) and get
> DIFFERENT answers, then having only one instance of the ANAME-target
> returned by the anycast auth (regardless of location) will be an
> "#EpicFail".
> Example:
>    - client in Los Angeles -> resolver somewhere in California -> ??? ->
>    AWS obfuscated-name -> California IP address (based on resolver IP, or
>    maybe client-subnet)
>    - client in Boston -> resolver somewhere in New England -> ??? -> AWS
>    obfuscated-name -> New York IP address (based on resolver IP, or maybe
>    client-subnet)
>    - If ??? is an ANAME, which does a tracking query FROM ONE LOCATION,
>    and mirrors that out to many anycast instances, then one of two results
>    will be seen in the mini-example case:
>       - The client in Los Angeles will receive the New York IP address, or
>       - The client in Boston will receive the California IP address
>       - According to the HTTP folks, neither of those is "acceptable"..
> Agree.
I think it finally depended on recursive's decision.
Authoritative wants to select the "best" response to client. ANAME returns
multiple responses to recursive, then recursive selects the "best".
Authoritative is hardly to know which RR is selected as response to the
Is authoritative's best response same with recursive's best response ?

The alternative is having EACH anycast instance for the auth server (which
> has an ANAME target of the AWS blob) doing its OWN tracking, which requires:
>    - Widely distributed DNSSEC signing (which requires placing the ZSKs
>    everywhere)
>    - Even more costly load out in every anycast location (multiply the
>    original Master lookups, by the number of anycast instances, times the
>    number of zones)
>> I'm not wedded to the current ANAME spec but we have plenty of experience
>> showing that it's possible to implement without causing disasters?
> The issue isn't whether it is possible to IMPLEMENT, it is whether it is
> feasible to OPERATE at scale.
> I don't doubt your implementation is easy, or any singular (non-anycast)
> implementation equally easy.
> The question is, would the incremental operational load, if you upped the
> zone count to O(10^6), be within reason?
> Or, how about the complexity of implementing the anycast stuff, especially
> differentiated answers?
> I submit that currently, in the face of possible externally-imposed update
> rates, it isn't possible to guarantee that the incremental operational cost
> would be negligible.
> On the other hand, the impact on resolvers (whose scaling is determined by
> actual query load, not the authority-update side of things), would be
> definitely marginal, if a solution that placed the burden on them was
> agreed-upon.
> Resolver operators can trivially shoulder the burden.
> Here's why: The operation difference would be, when QTYPE=A, Answer
> includes ANAME or WCRR, do another query for the RDATA, exactly as if the
> Answer had been a CNAME. Functionally identical, load-wise identical, to
> having an actual apex CNAME.
> For authority operators, scale is the problem, along with disproportionate
> load. The cost of tracking the siblings to ANAME records is the same,
> regardless of zone popularity. Amortized over a large query volume, and a
> small number of zones, it is easy to ignore the cost. However, when
> multiplied by a large number of zones, in the commodity range of domain
> names, it is not the case. You can't lose money on each and expect to make
> it up on volume.
> Brian
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致礼  Best Regards

潘蓝兰  Pan Lanlan