Hi All

[Barry Margolin]

In article <c9l2i9$2ql4$1 at sf1.isc.org>,
 "Servet Zeybek" <zeybek at mustang.europe.nokia.com> wrote:

>      I am working with DNS requests and responds for some time and i have
> some questions!!! (Im reading RFC 1035 but the info is not very clear for
> every request type)
> 
> 1 - MG (Mail Group Member): In RFC it says:  " A <domain-name> which
> specifies a mailbox which is a member of the mail group specified by the
> domain name" lets say, I have the name "example.com" to lookup  with this
> type of query(MG), does example.com specify a group? what does this query
> exactly mean? what should the answer be? When i try to look up the address
> (www.hotmail.com) i get a SOA answer, the address(www.google.com) i get a
> CNAME answer. Here i got confused, why 2 different answers, and why SOA and
> CNAME!!
> 2- MR (Mail rename domain name): RFC says; "A <domain-name> which specifies
> a mailbox which is the proper rename of the specified mailbox". Does that
> mean;  the name (example.com)  is assigned a mailbox(MB request), and MR
> gives an alternative mailbox for example.com? When i try this MR query with
> (www.google.com) i get a CNAME answer!!! isnt this illogical?

Both MG and MR were never really used and are now officially obsolete.

Anyway, the reason you get a CNAME answer for www.google.com is because 
that name is an alias.  When you follow the alias, the target name 
doesn't have MG or MR records, so you just get the CNAME record in the 
reply.

When a response indicates that the record you're looking for doesn't 
exist (either because the name doesn't exist or it doesn't have any 
records of the requested type), the domain's SOA record is returned in 
the Authority section for use in negative caching.

> 3- NULL : What is the purpose of this request? When i try this with
> www.google.com, i get a CNAME answer and with www.hotmail.com i get a SOA
> answer!!

This type of record isn't used for anything, it's just a reserved record 
type.  Again, the reason you get those responses is because 
www.google.com is an alias and www.hotmail.com doesn't have a record 
with the type you requested.

> 4- PTR(Domain name Pointer): how different is this from CNAME?

PTR records are for mapping IP addresses to names.  CNAMEs are for 
making one name an alias for another name.

> 5- what is "additional section processing"? I see this in RFC 1035?

When the answer contains references to other names, it's helpful to 
include useful information about those names, and this information goes 
in the Additional Records section of the reply.  For instance, an MX 
record contains the name of the mailserver for a domain; anyone looking 
up the MX record is most likely going to need to look up its address as 
the next step.  If the server knows this information, it should include 
it in the response to save the client from having to make another query.

-- 
Barry Margolin, barmar at alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***