Empty CNAME chain, should getaddrinfo() return EAI_NONAME or EAI_FAIL?

[Doug Barton]

Thanks Håvard and Chuck, not disagreeing below since I am genuinely 
confused, just trying to get it straight in my head.

On 04/28/2011 10:00, Chuck Swiger wrote:
> On Apr 28, 2011, at 3:23 AM, Havard Eidnes wrote:
> www.apple.com.  281 IN CNAME www.isg-apple.com.akadns.net.
>>> www.isg-apple.com.akadns.net. 60 IN CNAME www.apple.com.edgekey.net.
>>> www.apple.com.edgekey.net. 17295 IN CNAME e3191.c.akamaiedge.net.
>> ...
>>
>> As a matter of terminology, in the quoted example, I see a chain
>> of three CNAME records.  That's not what I would call an empty
>> CNAME chain.
>>
>> What I do see, though, is a CNAME chain of three CNAME records,
>> but where the ultimate target of the CNAME chain exists, but does
>> not have any data of the requested type.  Therefore, in the DNS
>> you get a NOERROR status code, and an answer section which does
>> not contain any records of the requested type.
>
> Agreed.  Akamai's EdgeSuite doesn't provide IPv6 AAAA records at this time, but e3191.c.akamaiedge.net does have an A record.

I understand what you're saying, but I've always referred to such a 
thing as an "empty CNAME chain" because it doesn't result in an address 
record at the end. Is there a more proper term for it?

>>> should getaddrinfo() return EAI_NONAME or EAI_FAIL?
>>
>> RFC 3493 says:
>>
>>    [EAI_NONAME]    The name does not resolve for the supplied
>>                    parameters.  Neither nodename nor servname were
>>                    supplied.  At least one of these must be supplied.
>>
>>    [EAI_FAIL]      A non-recoverable error occurred when attempting to
>>                    resolve the name.
>>
>> Which means that it should probably return EAI_NONAME; it's the least
>> bad error code among the ones listed in RFC 3493 for getaddrinfo(),
>> although one should not be mislead to think that this means that the
>> DNS said NXDOMAIN.
>
> +1 to this analysis as well.

The original question that started me down the rabbit hole was, "What 
error code should 'ping6 www.apple.com' return?" What confuses me here 
is that the node does actually "exist" in the sense that there is _an_ 
address record for it. So attempting to look at this from the standpoint 
of a user, the error message I get back (in our case, "hostname or 
servname not provided, or not known") doesn't make any sense. (Although 
admittedly the "does not resolve for the supplied parameters" part of 
the definition does seem to.) Since for the purpose of ping6 no AAAA 
record at the end of the chain is a non-recoverable error, _FAIL 
("non-recoverable failure in name resolution") seems to make more sense.

Is it possible that what we need is a new error code to designate 
"something exists here, just not what you asked for?" If _NONAME is 
intended to indicate that it seems overloaded. Alternatively I think we 
need to improve the language of our error messages. :-/


Thanks again,

Doug

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