Re: [dnssd] Review of draft-ietf-dnssd-mdns-dns-interop-01

["Hosnieh Rafiee" <[e-mail]>]

Hi Andrew,

> 
> […]
> 
> > Now the question is that is it possible also to cheat the recursive
> > resolver with mDNS responses while looking up for a domain?
> 
> No.  As I said in the WG session, the way that mDNS and DNS differentiate is
> using an in-band signalling mechanism, which is the final non-null label of the
> QNAME.  If that last non-null label is local, then it's mDNS; otherwise, it isn't.  If
> mDNS is responding to DNS queries, then it's just not following the mDNS
> protocol.
> 
> > - section 3
> > <snip> U-labels cannot contain upper case letters </snip>
> >
> > For some languages, upper case letter does not make it different
> > specially in some letters. Especially the languages that a word is the
> > result of attaching the characters together.  I think this is
> > specially true for non-european languages. Two examples are  Persian or
> Arabic.
> >
> > Therefore, one cannot differentiate between mDNS service and DNS names
> > with only considering that DNS cannot use uppercase U-labels.
> 
> Indeed, you cannot, and the document does not suggest you use this
> mechanism to tell whether something is a DNS name, right?

True

> > - section 4.2
> > It is not the requirement of DNSSD to use underscoll character, as far
> > as I can see it is only recommendation.
> 
> I don't see how.  The text you cite starts thus:

This part which says its is not a requirement of SRV records in general. What I understand is that following this structure is not the requirements. They are free to specify their namings

<snip>
Note that this usage of the "_udp" label for all protocols other than
   TCP applies exclusively to DNS-SD service advertising, i.e., services
   advertised using the PTR+SRV+TXT convention specified in this
   document.  It is not a requirement of SRV records in general.  Other
   specifications that are independent of DNS-SD and not intended to
   interoperate with DNS-SD records are not in any way constrained by
   how DNS-SD works just because they also use the DNS SRV record
   datatype [RFC2782]; they are free to specify their own naming
   conventions as appropriate.
</snip>
>    The <Service> portion of a Service Instance Name consists of a pair
>    of DNS labels, following the convention already established for SRV
>    records [RFC2782].
> 
>    The first label of the pair is an underscore character followed by
>    the Service Name [RFC6335].  The Service Name identifies what the
>    service does and what application protocol it uses to do it.
> 
> The underscore character is in fact part of the definition, and is the only way
> AFAICT that you'd be able to tell which part of the owner name is the
> <Service> portion of a Service Instance Name.
> 
> Best regards,
> 

Thanks,
Best,
Hosnieh