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The '''root servers''' are the top tier of nameservers which contain the necessary information to resolve each of the [[top level domain]]s of the internet.  There are currently several clusters of root servers.  Within each cluster, the member servers are spread out geographically both to minimize [[latency]] and to maximize [[fault tolerance]] for the internet as a whole.  The separate clusters service separate top level domains; if you initially query a root server which is not a member of the proper cluster it will give you the IP address of a server in the correct cluster.

Once given this address, you repeat your query to that server.  If you are still not in the right cluster to provide [[authoritative nameserver|authoritative]] answers for the top level domain, you will be forwarded again, and repeat your query again.  Once you arrive at the authoritative nameserver for your top level domain, you repeat your query to it, and it will point you to the authoritative nameserver for the second level domain.  This process can continue once or more for every subdomain level of the URL you wish to resolve.

For example, when you visited '''www.freebsdwiki.net''', either your own nameserver or your ISP's nameserver had to first resolve the [[DNS record types|A record]] to an IP address, by starting from the root servers and working its way downward.  At each step, it had to ask a progressively lower-hierarchy server the same question: where is '''www.freebsdwiki.net'''? Finally, the buck was passed all the way down to the bottom, and it got its final answer.  

That process can be repeated on the command line with the DNS tool [[dig]], and simplified a little, it looks a lot like this:

 workstation# '''dig @a.root-servers.net www.freebsdwiki.<font color="blue">net</font>'''
         ;; ->>HEADER<<- QUERY: 1, status: NOERROR, <font color="red">'''ANSWER: 0'''</font>, AUTHORITY: 13, ADDITIONAL: 14
         ;; AUTHORITY SECTION:   <font color="blue">NS      A.GTLD-SERVERS.net.</font>
         ;; ADDITIONAL SECTION:          <font color="blue">A.GTLD-SERVERS.net.</font>     172800  <font color="blue">IN      A       192.5.6.30</font>


First, we ask '''a.root-servers.net''' (which we found in the root hint file) where to find '''www.freebsdwiki.net'''.  It didn't know the <font color="red">answer</font>, but it did know you should be asking one of the <font color="blue">gtld-servers</font> about the .net TLD - so it told you that it knew an <font color="blue">NS</font> (nameserver record) for the .net part of your URL.  And since it figured you would just come right back and pester it for directions to that NS record anyway, it volunteered the corresponding <font color="blue">A record</font>, which contained its actual <font color="blue">IP address</font>, without making you specifically ask for it.

 workstation# '''dig @a.gtld-servers.net www.<font color="blue">freebsdwiki</font>.<font color="green">net</font>'''
         ;; ->>HEADER<<- QUERY: 1, status: NOERROR, <font color="red">'''ANSWER: 0'''</font>, AUTHORITY: 2, ADDITIONAL: 2
         ;; AUTHORITY SECTION:   <font color="blue">NS      ns1.jrssystems.net.</font>
         ;; ADDITIONAL SECTION:          <font color="blue">ns1.jrssystems.net.</font>     172800  <font color="blue">IN      A       66.154.114.98</font>
 
Following directions, next we ask <font color="blue">a.gtld-servers.net</font> the exact same question - but it doesn't know the <font color="red">answer</font> either.  However, it does know that the authoritative nameserver (<font color="blue">NS</font>) for '''freebsdwiki.net''' - the ''second'' level domain of the '''www.freebsdwiki.net''' - is ns1.jrssystems.net.  And just like a.root-servers.net, it gave you the corresponding <font color="blue">A record</font> before you could even ask.  Next step: <font color="blue">66.154.114.98</font>.

 workstation# '''dig @ns1.jrssystems.net <font color="blue">www</font>.<font color="green">freebsdwiki.net</font>'''
         ;; ->>HEADER<<- QUERY: 1, status: NOERROR, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2
         <font color="green">''';; ANSWER SECTION:              www.freebsdwiki.net.       300  IN      A       66.154.114.98'''</font>

Now we ask <font color="blue">ns1.jrssystems.net</font> for the exact same thing - '''www.freebsdwiki.net'''.  But since <font color="blue">ns1.jrssystems.net</font> is authoritative for both the third (www) and second (freebsdwiki) level subdomains of the .net top level domain, we don't get handed off to anybody else.  This time, we are given the final <font color="green">answer</font> to our query. And now that the DNS resolver has the <font color="green">A record</font> for '''www.freebsdwiki.net''', it extracts <font color="green">66.154.114.98</font> from it, hands that to your web browser, which then fetches the web page, and here you are.

[[Category:FreeBSD Terminology]]