Re: [cobalt-developers] Mail Settings

[Jeff Lasman <jblists@xxxxxxxxxxxxx>]

All of us here wrote:

> It is the documented method, it works perfectly on *my server*, that is my
> disclaimer. I have for each domain I host, shared IP or not:

Are you claiming that multiple PTR records for one IP# is documented
somewhere?  If so, please let us know where.

The well respected O'Reilly "DNS and Bind" specifically documents as
follows:

(page 65)
  There are a couple of things to notice about this data.  First,
  addresses should only point to a single name: the canonical name.
  Thus, 192.249.249.1 maps to wormhole and not to wh249.

True, it goes on to say:

(also page 65, immediately following)
  You can create two PTR records, one for wormhole and one for
  wh249, but most systems are not prepared to see more than one
  name for an address.

But frankly, I don't see that as very supporting.

For some additional clarification, here's an answer to a question to
"Ask Mr. DNS", I found at "http://www.acmebw.com/askmrdns/00172.htm";.

While I'm not sure exactly who Mr. DNS is, I have every reason to
believe it's Cricket Liu, who is well known and well respected as a DNS
consultant who knows what he's talking about.

Here's the question and the answer:

  At 02:34 PM 6/24/97 +0900, you wrote:
    
    >  also I am not sure wether one host with one ip address can has
two or
    >more Domain name , if one domain name have two ip mapped ,how to
set up 
    >in-addr.arpa record ? what the relationship between a host's domain
name
    >and host name in /etc/nodename , the domain name must be
    >hostname.my.domain ?  Would you please clarify these question with
me ?
    
    Any number of domain names can map to a single IP address. 
Similarly,
    a single domain name can map to multiple IP addresses.  In the first
case,
    you would normally choose to reverse map the IP address back to the
    official domain name.  BIND also supports attaching multiple PTR
records to
    the same domain name, but many programs don't understand how to deal
with
    multiple PTR records.
    
    I'm not sure what the "nodename" is.  On HP-UX, the nodename has to
do with
    HP's NS networking services, and is unrelated to DNS.
    
    Mr. DNS
    
    Acme Byte & Wire | http://www.acmebw.com/askmr.htm
    mr-dns@xxxxxxxxxx | (301) 571-0444 | (301) 564-0890 fax

It seems to me that since "many programs don't understand how to deal
with multiple PTR records it's dangerous to use them.

Of course, I, and Mr. Liu, and others, could well be wrong.

> A Record:  domain.xxx -->  ip address
> A Record:  www.domain.xxx -->  ip address
> MX Record: domain name field: domain.xxx
>            mail server field: www.domain.xxx
> 
> Also, since my dns server names are different than the default, I change my
> SOA records to the reflect proper values.

While this is fine, most of us define mail server names as either mail,
pop, or smtp.

> On both of my A Records I have a reverse pointer, as per documentation.
> Don't know if it is needed or not, never tested without it.

Okay, your call.  I'd expect that before you do that you read enough
references to understand why you would do it, but if you've chosen not
to do that, again, your call.

I strenuously test and document just about every response I give on this
and other lists, as I know that some readers herein will consider every
post as truthful.

> I have an entry as above for EVERY domain I host, no matter if shared or
> solo domain for ip, every domain gets an entry.

Since it hasn't broken yet for you or your clients, I suppose this is
good enough for you.  Obviously it's not good enough for me.

> >Still don't know what you mean by "to www.domain.xxx".  If you mean a
> >record like this:
> >
> >domain.com   IN MX 30 www.domain.com
> >
> >yes, that'll work, as long as there's an A record for www.domain.com.
> >That's exactly what I wrote above.
> 
> As written about, I have one MX record with domain.xxx --> www.domain.xxx
> (mail server).
> 
> >As I've written, maybe you're agreeing with me and it's just a matter of
> >semantics.
> 
> I agree with no one,

As I certainly now understand.

> we just may share the same opinion.

We do on the use of the MX record, though I didn't understand your
semantics the first time through.

> >Please be sure you're right when you pass information on mailing lists;
> >lots of people can learn bad habits that will eventually cause them
> >problems.
> >
> >Thanks <smile>.
> 
> I've been a programmer/support-geek for over 20 yrs, I am always careful in
> my posts.

I suppose if this were a contest I could point out that I was teaching
college computer systems and analysis courses almost twenty years ago.

As you've written earlier in your post, and as I've quoted above, 
> Don't know if it is needed or not, never tested without it.

I'll never forget the poster of the small airplane in the tree... the
line under it says "flying isn't inherently unsafe; it's just terribly
unforgiving of mistakes."

> If I am questioning shared advice I would note it. It is up to
> forums like this to correct incorrect posts - as your's at least questioned
> mine.

And as I'm attempting to correct the incorrect Cobalt DNS
documentation.  And some users' reliance on it.

> It made me re-look at my DNS to be sure that all understood what I
> was attempting to say and not have it misinterpreted.
> 
> The above is how my well-running system is setup. Comments/corrections are
> always welcome :)

Well, I certainly hope you'll consider the points I made above.  I fully
realize you may still choose to disagree with me.

Jeff
-- 
Jeff Lasman <jblists@xxxxxxxxxxxxx>
nobaloney.net
P. O. Box 52672
Riverside, CA  92517
voice: (909) 787-8589  *  fax: (909) 782-0205