Re: questions

["Conroy, Lawrence (SMTP)" <]

On 25 Nov 2003, at 9:53 am, Jim Reid wrote:

> > > > > > "Max" == Max Tulyev maxtul@localhost writes:
>     Max> And can I use other type of records than NAPTR? For example,
>     Max> TXT record to provide extra infromation about me, my name,
>     Max> company, physical address, etc?
>
> Of course. The DNS does not place any restriction on which resource
> record types may or may not exist for some name.
>
>     Max> So when I do call to ENUM-enabled application, it looks up my
>     Max> extra data and gives it to my peer with my phone number?
>
> Probably not. Though in theory the application could do that if it has
> prior knowledge that these other record types exist and contain that
> sort of information. An ENUM-aware application will expect to process
> NAPTR records, so it's unlikely to lookup other types of records for
> an ENUM name. Or make sense of any TXT record (say) if such a thing
> existed. How could the application know that this TXT record encoded a
> postal address? Even harder would be determining what that postal
> address was for or to do anything sensible with it.
Hi Jim, Max, Folks,

Yes, one can add anything - it's a domain. Strictly, there are a couple
of issues in practice.
(i)  ENUM domains I've seen "out there" tend to have more than one 
NAPTR.
     Making a request for NAPTRs can return an answer that's several 
hundred
     bytes long. If there are other Resource Record types (such as TXT) 
then
     the answer can grow beyond 500 octets. This can be a problem as 
ALL the
     resource records won't fit into a UDP answer, so it may be 
truncated.
=>   If you expect there may be TXT records, do two queries - one for 
NAPTRs
     and one for TXT records (or MX, or ...).
     Note that (as Jim points out) one can get a mail address in a 
NAPTR.

(ii) Many DNS servers return resource records in a random order; thus if
     there's more than one TXT record, you have to guess which one to 
handle
     first.

(iii)TXT records do ASCII - thus there can be an issue with a useful 
address
     [or your .sig, Max - the "(MT6561-RIPE, 2:463/253@localhost)" is OK, 
but...]

(iv) In some countries, folk still have a 20th Century attitude to 
privacy;
     Doing a query on a phone number will get you the name (if there's 
a TXT
     record with this data). Some people consider this "sensitive" data.
=>   It's an "opt-in" service; such paranoid folk won't put in a TXT 
Record
     with their name, so you can't expect one to be available always. A 
query
     for TXT records may return no content.
Plus... you will be doing two DNS queries, even if there's no data for 
the
second; that will have a major impact on DNS query volume. I think 
that's
what Jim meant when he said "prior knowledge" - to just guess and 
always do
a second query for TXT records is not "polite".

Having said that, we run a split-view DNS setup; for "internal" use we 
have
TXT records in the zones, whilst the "external" view doesn't. This 
seems to
be a typical setup for a company, and some folk even have these as 
global
entries.

(Our lookup web at <http://www.sienum.co.uk/lookup.php> will try to find
a TXT record and display it, if one exists - we're not polite.
For example, try 
<http://www.sienum.co.uk/loopup.php?%2B878108781087810>)


One could instead use a NAPTR  in the ENUM domain with a web URL 
pointing
to a .PNG of the name (and/or picture). This could be used:
- as a link to a distributed directory to give name and picture, if this
  is not considered a privacy issue, or
- with a lookup of the called number to give a graphical caller display.

all the best,
  Lawrence