DNS PTR Question

Daniel B. Thurman dant at cdkkt.com
Wed Feb 24 21:59:15 UTC 2010


On 02/24/2010 01:19 PM, James Wilkinson wrote:
> Daniel B. Thurman wrote:
>> I am trying to get a handle on how to properly
>> assign DNS PTR records, given these conditions:
>>
>> 1) Single machine containing:
>>     a) DNS Server
>>     b) Sendmail Server
> <snip>
>> The problem here is assigning the PTR, since
>> only ONE reverse IP address is allowed.  In
>> the above case, which will it be, ns1.domain.com
>> or mx1.domain.com?  Discovery led to the last
>> "scanned" entry, which is mx1.domain.com
>>
>> Why is this a potential problem?
>> + One that I can think of, is security verification
>>   such as some programs do a reverse IP check to reduce
>>   phishing/spamming?
>
> Alternate idea: have both mx1 and ns1 as CNAMEs to the “real” host name,
> and put that “real” host name in the reverse DNS.
>
> Don’t forget that you have to have your MX records pointing to that A
> record: MX pointing to CNAMEs is Not Allowed.
>
> Hope this helps,
>
> James.
>

So, basically you are saying this?

Forward zone contains:
======================
$TTL 172800
@        IN SOA host1.domain.com. admin.domain.com. (
                3818          ; serial
                3H            ; refresh
                15M           ; retry
                1W            ; expiry
                1D )          ; minimum
; ==========[Nameservers]=================
@            IN NS       host1.domain.com.
; ==========[Mail Exchangers]=============
@            IN MX   10  host1.domain.com.
; ==========[Machines]====================
ns1          IN CNAME    host1.domain.com.
mx1          IN CNAME    host1.domain.com.
host1        IN A        10.1.0.1
[...]


Reverse zone contains:
======================
$TTL 172800
@       IN SOA ns1.domain.com admin.domain.com (
        3818          ; serial
        3H            ; refresh
        15M           ; retry
        1W            ; expiry
        1D )          ; minimum
;============[Top-Level]==================
@       IN NS           host1.domain.com.
;============[PTRS]=======================
1       IN PTR          host1.domain.com.
[...]




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