Re: DRAFT-IETF-X400OPS-DNSX400MAPS-03.TXT

[Claudio Allocchio - [phone] <[e-mail]>]

Hallo Christian,

>X-Posting-Date: Tue, 23 Nov 1993 18:41:32 +0100
>Original_From: Christian Huitema <[e-mail]>
>                   
>Claudio,
>
>I like your proposal, but for one point. You propose to store both mapping 1
>and mapping 2 in the same records. This is fine, but you should only use one
>format.
 
but actually we use one single format, it is:

     822-domain   IN  PX  0  mapping-rule2

and

     x400-domain  IN  PX  0  mapping-rule1


1>	*.nrc.it.             IN  PX  0  nrc.it#PRMD-nrc.ADMD-acme.C-it	

the above is case 822-domain in PX 0 mapping-rule2, thus it is OK;

2>	*.ADMD-acme.X42D.it.  IN  PX  0  ADMD-acme.C-it#it

the above is case x400-domain  IN  PX  0 mapping-rule1, thus it is OK;

3> 	*.ADMD-acme.X42D.it.  IN  PX  0  it#ADMD-acme.C-it

the above is NOT allowed by our proposal, as it is contains a mapping-rule2
or a gate table entry as an answer to a query for an X.400 domain, while you 
must always get a mapping-rule1 for a query starting from an X.400 domain.
 
>Reason: the process always know in which direction it is converting, so it
>will have no problem knowing whether to use the righthand side or the left
>hand side of the #. 

Yes, the gateway will always know wich side of the # is the 822-domain and
which side is the X.400 domain, even if it gets a mapping-rule1 written with
the 2 parts swapped, i.e. example 3> above. One could also use this convention,
but it could be confusing, as we speak of storing "mapping rule 1" and
"mapping rule 2" which has their own sintax with their clear positioning
on the left and right side of the # sign of their elements.

>But there are many chances that usage of CNAME or other
>search strategies result in a mapping 1 being retrieved when mapping 2 was
>desired. 

The examples in the draft are easy and symmetric cases, but as we studied
some time ago, mapping rules are not symmetric, and the match algorhytm
gives too many cases where one should insert a CNAME. More over, during
the discussion with the DNS group (namedroppers) and expecially with their
chairman (Rob Austin) it was pointed out that CNAME strategies should not
be used too heavily: "make it simple, make it straight" was the absolute
reccomendation, with a strong accent to avoid aliases techniques. 

>You should either have one RR type and one syntax, or two rr types if
>you insist on different syntaxes.

do you propose something like:

     *.nrc.it.             IN  PX  0  nrc.it#PRMD-nrc.ADMD-acme.C-it
     *.PRMD-nrc.ADMD-acme.X42D.it.  IN  CNAME  nrc.it

as "one RR, one syntax and used CNAME" ? but this does not work for
asymmetric mappings.

or just:

     *.nrc.it.             IN  PX1  0  nrc.it#PRMD-nrc.ADMD-acme.C-it
     *.PRMD-nrc.ADMD-acme.X42D.it.  IN  PX2  0  PRMD-nrc.ADMD-acme.C-it#nrc.it

with 2 RR with identical syntax?

Maybe I do not understand exactly what you mean with your last sentence...
could you just send us an example?

Thanks!
Claudio  
 
(last minute note: there is quite a strong pressure coming from the x.400
providers to use the new x.400 space in DNS, i.e. the name structure
following the X.400 hierarchy hooked under the country codes top level
domains, also for mail sending information for MTAs, exactly as for MX
records for SMTP mail. This is something different from our proposal,
but it clearly works only in the proposed X42D.cc space.)