Inherited DNS

[Joseph S D Yao]

On Fri, Sep 15, 2000 at 09:37:16AM -0500, Edmiston, Jerry wrote:
> Recently, I inherited the DNS responsibilities here at work. I've worked
> with DNS before and am familar with the structure and purpose of DNS. But
> some things in this DNS environement are very confusing. Why would a printer
> be defined to DNS? Why would multiple A records with the same IP number be
> assigned to multiple host names? Why would just about every A record entry
> (and there are alot) have an MX record? To me these are errors and should be
> corrected. No one will admit to the entries, only pointing to people that
> have long gone, but they keep insisting that they are needed. Anyway, am I
> missing something or is this truly a cluster of DNS errors. Any help would
> be grealy appreciated. Thanks in advance...

None of these are errors.

Some may not correspond to reality, but all of these have legitimate
reasons for existing, in some configuration.

Since you were gone, I guess, a lot of printers are hooked directly off
of networks instead of to servers.  These printers need network names
and IP addresses.

One server may server multiple purposes.  It may be the name server,
the mail server, the Web server, and other servers.  It may be
desirable to use different names for each function, so that you can
move the function without defining the name.  One way to define these
is with CNAME records, telling what the "canonical name" is for, e.g.,
"www":

orpheus		IN A		10.0.0.42
web		IN CNAME	orpheus
www		IN CNAME	orpheus
oracle		IN CNAME	orpheus
real-audio	IN CNAME	orpheus

There are several cases in which you NEED an "A" record instead of a
CNAME, though.  The name server and the mail server names must refer to
A records.  The domain name - should you for some odd reason want it to
have an IP address - must use an A record; and in fact, any names that
you want to distinguish by having other records attached to them may
NOT have CNAME records:

@		IN A		10.0.0.42
		IN NS		ns
		IN MX		mailhost
ns		IN A		10.0.0.42
		IN MX		mailhost
mailhost	IN A		10.0.0.42
		IN MX		mailhost
elvis		IN A		10.0.0.42
elvis		IN MX		rocker
mozart		IN A		10.0.0.42
mozart		IN MX		classy

Hey!  Why all the MX records?  Well, some are to redirect mail
differently.  But most are to the same mail host.  That way, if someone
should send mail to a random workstation [Melissa has her e-mail return
address set to melissa at ws005-dhcp.workplace.com instead of
melissa at workplace.com], the mail gets sent to the right place anyway.
And 'sendmail' on that machine should be configured to accept e-mail
sent to any of those hosts, and strip off the host name.

Hope this helps.

-- 
Joe Yao				jsdy at cospo.osis.gov - Joseph S. D. Yao
COSPO/OSIS Computer Support					EMT-B
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