[PLUG] Victor is trying to understand DNS

Ed Sawicki ed at alcpress.com
Sun Oct 14 17:50:13 UTC 2007


Bill Barry wrote:
> On 10/14/07, Ed Sawicki <ed at alcpress.com> wrote:
>> Victor's not wrong. A DNS nameserver can resolve an IP address
>> to a name as well as the reverse. It's just that resolving a
>> name to an IP address is more common.
>>
>>
>> Ed
>> _______________________________________________
> 
> 
> Reverse DNS, i.e. resolving an ip address to a name is as far as I
> understand a slightly different process than regular Forward DNS. It
> is indeed handled by nameservers, but  via a different route. If the
> ip address is a.b.c.d. It looks up a PTR record in the domain name
> d.c.b.a.in-addr.arpa.  The control of these different routes is in
> different hands.
> 
>  When I register a domain, I have control over which IP address  that
> domain name points to. I tell the domain name registrar the
> nameservers I will be using for that domain and I tell the nameservers
> which IP address I will be using for that domain by creating an A
> record.
> 
> I do not have the same control over the reverse DNS. That control is
> in the hands of the ISP that gave me the address. If I want to have
> the reverse DNS work correctly I must get the ISP who gave me the IP
> address to change the PTR record  which points from an IP address to a
> domain name. They control it, not me.  Can they delegate that
> authority to me?

Yes, they can - easily. But many or most ISPs won't unless you're
an important customer, have a lot of IP addresses, etc. I suspect
that many ISPs use software rather than human intelligence to
handle the reverse DNS zones, so they're locked in by the
functionality of their software.


  How do they do that?

They just point the reverse DNS "name" to your DNS server.
Your server is configured to answer for those names.
It's exactly the same concept as forward DNS except, as
you point out, control is in different hands in the chain
above you.


> 
> Since I have never done this, the questions are. Is all of this
> correct? If so how do you go about setting up Reverse DNS.  Do you
> just email the ISP and ask them to do it or is there some other
> mechanism?

Yes, you ask the ISP to set it up for you and you wait for
their reply that tells you they won't or can't.
:-)

Ed

> 
> Thanks,
> Bill



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