Virtual DNS questiona and reverse lookup table conflicts

John Cornelius jc at hangarpilot.net
Sun Dec 7 17:19:03 UTC 2008



Daniel B. Thurman wrote:
>
> [WARNING!  This is a long discussion!]
>
> Is it possible to have a single DNS server support
> two different domain names, with each domain
> name having it's own forward and reverse lookups?
>
> The problem I seem to run into is that of reverse
> lookups; I cannot seem to figure out just how to
> have common reverse IP lookups separated so that
> it returns the correct domain name based on the
> domain name itself.
>
---------------Snip------------------
>
> My goal here is to support redundancy by having two
> separate servers, each supporting two domain names
> so that if one server drops dead, the other server will
> take over and also, I really do not want to have 4 different
> servers, two for each domain name so, it is about cost
> as well.
>
> Does this scenario make any sense at all?
>
> I have looked for examples on the Internet but I could
> not find anything that can shed some light on this. Perhaps
> someone can point me in the right direction or - perhaps this
> is a nutty idea and there is a better way?
>
> Kind regards,
> Dan
>
The difficulty with what you want to do may be that you shouldn't want 
to do it.

DNS is actually two sets of services namely address resolution for 
domain names and name resolution for Internet addresses.

In the first instance any number of domain names can resolve to a single 
address i.e., mail.x.net and www.y.net can both resolve to the same IP 
address. This information is set up for each domain irrespective of what 
the IP address is. Indeed, and domain name can resolve to several IP 
addresses for load balancing or redundancy.

In the second instance an IP address can only resolve to a single 
Internet domain name and the reverse lookup resolution often is done on 
a computer that is different than the computer providing the forward 
resolution because it must be done by the entity that owns the network 
e.g., your ISP.

When a remote host looks up the name of a computer through reverse DNS 
lookup it only provides the address to the server registered as the 
owner of the address space and each address can have only one 
(canonical) name at any given instant. If it were otherwise the name 
server would never know which name to return in response to the reverse 
lookup query.

-- 

John Cornelius

"I may not be totally perfect, but parts of me are excellent."
Ashleigh Brilliant, 1979




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