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Posted to server-dev@james.apache.org by "Stefano Bagnara (JIRA)" <se...@james.apache.org> on 2006/03/25 18:52:19 UTC
[jira] Resolved: (JAMES-441) Add an option to support aliases
(CNAME) for MX records
[ http://issues.apache.org/jira/browse/JAMES-441?page=all ]
Stefano Bagnara resolved JAMES-441:
-----------------------------------
Fix Version: 2.3.0a2
Resolution: Fixed
The test written passes with the current trunk.
Not sure what fixed this: maybe the upgraded dnsjava library.
> 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
> Fix For: 2.3.0a2
>
> 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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