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From: rickert@mp.cs.niu.edu (Neil Rickert)
Newsgroups: comp.protocols.tcp-ip.domains
Subject: Re: PTR records of gateways on the Internet
Message-ID: <1991Jan10.051543.8831@mp.cs.niu.edu>
Date: 10 Jan 91 05:15:43 GMT
References: <1991Jan9.195641.17628@slcs.slb.com>
Organization: Northern Illinois University
Lines: 60

In article <1991Jan9.195641.17628@slcs.slb.com> 7thson@slcs.slb.com (Chris Garrigues) writes:
>(...)
>Needless to say, in the process, I discovered that some administrators
>appear to have rather bizzare ideas of how to set up these records.
>
>a) I found PTR records that pointed to names that weren't in the DNS.
>
 What, if anything, is wrong with that?  If a system makes outbound
telnet/ftp etc connections, good Internet manners requires that the
system identify itself.  If the same system refuses all inbound connections
there is no reason for it to have an A-record.  Indeed such a record might
even be undesirable.  Perhaps a case could be made that it should have
an HINFO record.  Or perhaps it should have a CNAME record identifying
a system whose administrator manages the indicated system.

 For example what do you do with a PC which is not always turned on, which
is not running TCP software except when making outbound calls.

 Or what do you do with 'dial SL/IP' where different hosts can share
a common Internet address?

>b) I found PTR records that pointed to names that mapped back to
>different addresses.

 This is exactly what you would expect in the suggested example above
if the name on the PTR were a CNAME for another system with the same
administrator.

>c) Many of these addresses mapped into names which only had one address.
>This either means that no entry was made for the other name or the two
>names are entirely unlinked.

 Perhaps they are administratively linked.

 You might start by looking at an example I brought up (with no satisfactory
response) in the bind mailing list.  Specifically the samples that come
with the bind software suggest you use a PTR to map 127.0.0.1 to
'localhost', and that you have an A-record mapping 'localhost.your.domain'
to '127.0.0.1'.  Isn't this the type of inconsistency you are complaining
about?

>Does anybody besides me think that a RFC that clarified what a domain
>administrator MAY, SHOULD, and MUST do would be useful to point at when
>stumbling over things like these.  Examples might be:
>
 While I agree some clarification is needed, it cannot be a precise as you
would like.  The Internet has evolved in ways probably not envisioned
when 'bind' was designed.

 Personally I am much more troubled by the cases where the different name
servers for a domain have mutually inconsistent data - presumably reflecting
an intermural dispute within the domain. (In at least one case I know this
is not just a matter of delayed updating, unless the TTLs are 1 year or
more).

-- 
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  Neil W. Rickert, Computer Science               <rickert@cs.niu.edu>
  Northern Illinois Univ.
  DeKalb, IL 60115                                   +1-815-753-6940