RR conflicts

Harold Pritchett harold at uga.edu
Sat Jul 31 15:14:09 UTC 1999


Michael Voight wrote:
> 
> It violates the rules...
> 
> Why do you need it? Why not make it an A record, or change the MX record
> to an A record.  I know of no modern mailers that will not send mail
> based on the A record. With a single MX record, I don't see an
> advantage.

You need it because properly configured mailers will ALWAYS request the
MX
record first, and if not found then go after the A record.  By having
the MX record, you cut down by half the number of requests.
 
> Actually, I think you do just as well by sending mail to the CNAME
> record and don't need a separate MX record.

If you send mail to the CNAME record, then it will pick up ALL of the
records of the cannonical name pointed to by the CNAME record.  So if
you want to do this, the right answer is:

morgank		in	a		1.2.3.4
		in	mx	0	morgank
emc		in	cname		morgank

There is another problem here.  Sendmail, and some other mailers, are
configured "out of the box" to convert hames to the "cannonical name.:

This means that if you send mail from, in your case, user at emc.ms.com
the software, when it transmits the message will convert the address
to user at morgank.ms.com, the cannonical name.

About the only way we have found to fix this, is to not use cname
records at all, but to just have two A records and two MX records.

Somethink like this

morgank		in	a		1.2.3.4
		in	mx	0	morgank
emc		in	a		1.2.3.4
		in	mx	0	emc

Now, the question is what to do about the PTR records for this host...

I personally put both names in the PTR record, knowing that not all
hosts on the net can properly handle it.

Harold Pritchett
The University of Georgia
> 
> Michael
> 
> Sam Shteingart wrote:
> >
> > I have the following entries in my zone file:
> >
> > emc     MX      10 morgank
> > morgank A          1.2.3.4
> > emc     CNAME      morgank
> >
> > bind 4.9.6 had no problems with the above.  bind 8.2.1, however,
> > complains:
> >
> > named[27358]: emc.ms.com has CNAME and other data (invalid)
> > master zone "ms.com" (IN) rejected due to errors (serial 933102907)
> >
> > Why cannot I have CNAME and MX records with the same names?
> >
> > --
> > Sam Shteingart   Morgan Stanley Dean Witter Co.
> > Phone: (212) 762-2377  Fax: (212)762-1009
> >
> > e-mail:  samsh at ms.com


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