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What came first: the CNAME or the A record?

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Re: What came first: the CNAME or the A record?

#11

Post by stackskipton »

renewiltord wrote: post #7

Nice analysis. Boy I can’t imagine having to work at Cloudflare on this stuff. A month to get your “small in code” change out only to find some bums somewhere have written code that will make it not work.

Or when working on massive infrastructure like this, you write plenty of tests that would have saved you a month worth of work.

They write reordering, push it and glibc tester fires, fails and you quickly discover "Crap, tests are failing and dependency (glibc) doesn't work way I thought it would."

Re: What came first: the CNAME or the A record?

#13

Post by mmastrac »

patrickmay wrote: post #3

A great example of Hyrum's Law: "With a sufficient number of users of an API, it does not matter what you promise in the contract: all observable behaviors of your system will be depended on by somebody." combined with failure to follow Postel's Law: "Be conservative in what you send, be liberal in what you accept."

Postel's law is considered more and more harmful as the industry evolved.

Re: What came first: the CNAME or the A record?

#14

Post by steve1977 »

I don't find the wording in the RFC to be that ambiguous actually.

> The answer to the query, possibly preface by one or more CNAME RRs that specify aliases encountered on the way to an answer.

The "possibly preface" (sic!) to me is obviously to be understood as "if there are any CNAME RRs, the answer to the query is to be prefaced by those CNAME RRs" and not "you can preface the query with the CNAME RRs or you can place them wherever you want".

Re: What came first: the CNAME or the A record?

#16

Post by forinti »

> While in our interpretation the RFCs do not require CNAMEs to appear in any particular order, it’s clear that at least some widely-deployed DNS clients rely on it. As some systems using these clients might be updated infrequently, or never updated at all, we believe it’s best to require CNAME records to appear in-order before any other records.

That's the only reasonable conclusion, really.

Re: What came first: the CNAME or the A record?

#18

Post by n2d4 »

mmastrac wrote: post #13
patrickmay wrote: post #3

A great example of Hyrum's Law: "With a sufficient number of users of an API, it does not matter what you promise in the contract: all observable behaviors of your system will be depended on by somebody." combined with failure to follow Postel's Law: "Be conservative in what you send, be liberal in what you accept."

Postel's law is considered more and more harmful as the industry evolved.

Very much so. A better law would be conservative in both sending and accepting, as it turns out that if you are liberal in what you accept, senders will choose to disobey Postel's law and be liberal in what they send, too.

Re: What came first: the CNAME or the A record?

#19

Post by paulddraper »

> RFC 1034, published in 1987, defines much of the behavior of the DNS protocol, and should give us an answer on whether the order of CNAME records matters. Section 4.3.1 contains the following text:

> If recursive service is requested and available, the recursive response to a query will be one of the following:

> - The answer to the query, possibly preface by one or more CNAME RRs that specify aliases encountered on the way to an answer.

> While "possibly preface" can be interpreted as a requirement for CNAME records to appear before everything else, it does not use normative key words, such as MUST and SHOULD that modern RFCs use to express requirements. This isn’t a flaw in RFC 1034, but simply a result of its age. RFC 2119, which standardized these key words, was published in 1997, 10 years after RFC 1034.

It's pretty clear that CNAME is at the beginning.

The "possibly" does not refer to the order but rather to the presence.

If they are present, they are are first.

Re: What came first: the CNAME or the A record?

#20

Post by paulddraper »

steve1977 wrote: post #14

I don't find the wording in the RFC to be that ambiguous actually. > The answer to the query, possibly preface by one or more CNAME RRs that specify aliases encountered on the way to an answer. The "possibly preface" (sic!) to me is obviously to be understood as "if there are any CNAME RRs, the answer to the query is to be prefaced by those CNAME RRs" and not "you can preface the query with the CNAME RRs or you can p…

100%

I just commented the same.

It's pretty clear that the "possibly" refers to the presence of the CNAME RRs, not the ordering.

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