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From "Stefano Bagnara (JIRA)" <server-...@james.apache.org>
Subject [jira] Assigned: (JAMES-441) Add an option to support aliases (CNAME) for MX records
Date Thu, 02 Mar 2006 21:06:47 GMT
     [ http://issues.apache.org/jira/browse/JAMES-441?page=all ]

Stefano Bagnara reassigned JAMES-441:

    Assign To: Stefano Bagnara

> Add an option to support aliases (CNAME) for MX records
> -------------------------------------------------------
>          Key: JAMES-441
>          URL: http://issues.apache.org/jira/browse/JAMES-441
>      Project: James
>         Type: Improvement
>   Components: DNSServer
>     Versions: 2.2.0
>     Reporter: Stefano Bagnara
>     Assignee: Stefano Bagnara

> rfc2181 ((Clarifications to the DNS Specification) clearly explain that this should not
be done:
> 10.3. MX and NS records
> The domain name used as the value of a NS resource record, or part of
> the value of a MX resource record must not be an alias.  Not only is
> the specification clear on this point, but using an alias in either
> of these positions neither works as well as might be hoped, nor well
> fulfills the ambition that may have led to this approach.  This
> domain name must have as its value one or more address records.
> Currently those will be A records, however in the future other record
> types giving addressing information may be acceptable.  It can also
> have other RRs, but never a CNAME RR.
> Searching for either NS or MX records causes "additional section
> processing" in which address records associated with the value of the
> record sought are appended to the answer.  This helps avoid needless
> extra queries that are easily anticipated when the first was made.
> Additional section processing does not include CNAME records, let
> alone the address records that may be associated with the canonical
> name derived from the alias.  Thus, if an alias is used as the value
> of an NS or MX record, no address will be returned with the NS or MX
> value.  This can cause extra queries, and extra network burden, on
> every query.  It is trivial for the DNS administrator to avoid this
> by resolving the alias and placing the canonical name directly in the
> affected record just once when it is updated or installed.  In some
> particular hard cases the lack of the additional section address
> records in the results of a NS lookup can cause the request to fail.
> But having Sendmail, postfix, qmail, and exim, around that support the aliased MXs simply
let the sysadmin to not follow the RFC because "most" mta support the "trick".
> This article is related:
> http://www.mengwong.com/misc/rfc1912-is-wrong.html

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