how DNS client perform reverse lookup

[Keith Ng]

Kevin Darcy wrote:
> Keith Ng wrote:
> 
> 
>>Barry Margolin wrote:
>> 
>>
>>
>>>In article <ct3ioj$1qll$1 at sf1.isc.org>, Keith Ng <ngkeith at triumf.ca> 
>>>wrote:
>>>
>>>
>>>   
>>>
>>>
>>>>Hi,
>>>>
>>>>Would someone tell me how DNS client perform reverse lookup? Is there 
>>>>any root servers like forwards lookup for the in-addr.apra domain?
>>>>     
>>>>
>>>
>>>They start from the normal root servers.  These servers have delegation 
>>>records for in-addr.arpa, just like they do for com, net, etc.  The 
>>>client servers follow this reverse delegation in exactly the same way 
>>>that they follow forward delegations.  As far as the nameservers are 
>>>concerned, there's no difference between forward and reverse DNS; 
>>>everything is just arbitrary labels to the servers and resolvers.
>>>
>>>   
>>>
>>
>>Thanks guys,
>>
>>I did not realize that the root servers for TLD are also responsible for 
>>the in-addr.arpa domain.
>>
>>Now it is making sense to me.
>>
> 
> I think you're still not quite getting it. The root servers are servers 
> for the root zone. TLD servers are servers for a particular TLD zone 
> (i.e. the apex zone of the domain). in-addr.arpa is neither the root 
> zone nor the apex zone of a TLD. It's delegated *underneath* the .arpa 
> TLD. The fact that the same boxes that serve the root zone and the .arpa 
> TLD also serve the in-addr.arpa zone is only a coincidence, and may 
> change in the future. There's no hard requirement for a zone cut to 
> appear at every domain/subdomain boundary, but in this particular case, 
> there's two levels of delegation from root to in-addr.arpa. A recursive 
> resolver should, however, be able to find anything in the namespace by 
> following the delegations down (assuming of course that it can speak to 
> the authoritative nameservers at each delegation level).
> 
> - Kevin
> 
> 
> 
Kevin, thanks for verifying that for me.

Keith