Resolving CNAMEs when pointing to another domain

Eric A. Hall ehall at ehsco.com
Tue May 9 02:23:56 UTC 2000


> The fly in the ointment is/(may be) that lbnamed isn't a recursive
> server, and it's only authoritative for "mydomain.com".

Yup, that's the problem. Your CNAME alias points to a canonical name in
another domain, but the server isn't performing recursion so it isn't
fetching the additional data. Your resolver probably isn't iterative
either (not many are), so the only data you will get from the resolver
will be the CNAME answer. If you want to complete the query, you'll have
to reissue the query yourself.

Note that if the requested RR is available in one of the server's zones
(or in the cache in this case), then the data will be answerable without
any recursion being required.

> When is it appropriate to add information to the "additional records"
> section, and when is it mandatory?  RFC 1035 says:
>    CNAME RRs cause no additional section processing, but name
>    servers may choose to restart the query at the canonical name
>    in certain cases.  See the description of name server logic in
>    [RFC-1034] for details.

Most servers will complete a query that returns a CNAME RR, since most
of the time the next query will be the requested RR for the canonical
name of the alias. Except when they're told not to do so, of course.

-- 
Eric A. Hall                                            ehall at ehsco.com
+1-650-685-0557                                    http://www.ehsco.com



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