On Apr 28, 2011, at 11:52 AM, Doug Barton wrote:
>> 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?
RFC-1034 talks about CNAME chains:
"Of course, by the robustness principle, domain software should not fail when
presented with CNAME
chains or loops; CNAME chains should be followed and CNAME loops signalled as
an error.
...and the recursive query algorithm:
"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.
- A name error indicating that the name does not exist. This
may include CNAME RRs that indicate that the original query
name was an alias for a name which does not exist.
- A temporary error indication."
This phrase "name does not exist" appears to best be represented as EAI_NONAME.
>>>> 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?"
Well, it appears that some other folks expect EAI_NONAME:
http://www.freebsd.org/cgi/query-pr.cgi?pr=156684
...and the MacOSX version of ping6 uses it for this case:
% ping6 www.apple.com
ping6: getaddrinfo -- nodename nor servname provided, or not known
> 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.
If the nameserver returned a failure (ie, NXDOMAIN, SERVFAIL), then I would
agree with EAI_FAIL.
However, it didn't fail; you just asked a question which it answered
successfully by providing all of the data which matched the query type; ie, the
CNAMES up to the end of the chain, but not including the A record which
terminates it, since you asked for an AAAA instead.
> 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. :-/
As Harvard mentioned, EAI_NODATA? :-)
Regards,
--
-Chuck
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