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Can someone correct/explain DNS a little better...


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#1 David Ashcroft

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Posted 25 June 2014 - 01:39 PM

Hi, here is my perception of what DNS does in a basic form, i was wondering if someone could expand upon it for me and/or correct me on what i understand it as being as i think i am wrong somewhere along the line.

 

So, you request a website such as google.com and your computer obviously needs to use DNS to find the IP address.

 

So the computer checks the local cache file and any cache on server on the local network, assuming it cannot be found it looks further, such as at a DNS server for your ISP. Assuming it cannot be found it asks a root name server that should know where it is. The root server tells the request where the .com TLD name server is, the request then finds the .com server and goes there. The .com server tells it about google. The full request is then returned to the requester with the IP address that corresponds to the domain.

 

What have i got wrong here??

 

Thanks! :) 

 

 



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#2 Grinler

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Posted 25 June 2014 - 01:51 PM

WHen you attempt to connect to a hostname, your computer does these steps:

1. Tries to resolve the hostname via your DNS cache or HOSTs file.
2. If that fails, it then queries your configured DNS server. That DNS server checks its cache and if its found returns the ip address.
3. If its not found, your configured DNS server then queries the root servers for the server that is in charge of the TLD (.com, .edu, .org, etc).
4. It then queries that TLD server for the server responsible for the domain name.
5. It then queries that server for the IP address.

Almost all DNS requests these days utilize a cache and only a full retrieval (actually querying the root server) is done when the TTL (time-to-live) for the hostname expires.

#3 David Ashcroft

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Posted 25 June 2014 - 02:10 PM

Thanks for that! It is steps 3 and 4 i am getting confused with!

 

3. If its not found, your configured DNS server then queries the root servers for the server that is in charge of the TLD (.com, .edu, .org, etc).
4. It then queries that TLD server for the server responsible for the domain name.

 

So in step 3 there are root servers around the world (i assume in large clusters) that basically have the info on where to go to find the TLD servers... Once this is found it then does step 4 and goes to the TLD server responsible for .com domains to find GOOGLE.com ? 



#4 Grinler

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Posted 25 June 2014 - 02:15 PM

Correct each TLD must be included in a root server or any domains under it will never be found by the rest of the world.

Yes, query ROOT for server responsible for .COM domains. Query .COM root server for info on who is responsible for google.com, query google.com's servers for IP address.

Most of these steps never happen as they are in cache.

#5 David Ashcroft

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Posted 25 June 2014 - 02:27 PM

Excellent thank you!! :) Is that were authoritative and non-authoritative results come in? 

 

Thanks for all this btw :D  :bananas:



#6 x64

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Posted 25 June 2014 - 02:39 PM

Authoritative = The name server returning the result is responsible for the record being returned (effectively one of the official DNS servers for the domain).

 

Non Authoritative = the server returning the result is returning data data retrieved from another source.(For example your ISPs DNS resolver DNS servers which do not hold any zones themselves [but go off and find resolve queries on behalf of their client], would always return non-authoritative data)

 

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#7 David Ashcroft

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Posted 25 June 2014 - 02:40 PM

Thanks to both of you, cleared that right up for me :D 

 

Thanks again!!! :D 






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