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trying to understand the DNS set up !

Posted on 2009-04-07
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Last Modified: 2012-05-06
I am just trying to understand the DNS setup and how its working ... I've a DNS server which is pointing to itself and has all the lookup records ... There must be some point where this DNS server has to talk to my ISP's DNS server to resolve requests ... Where can I find that DNS entry for ISP coz i check the router or the pix that has the connection out to the internet and it has no such command configured as  "ip name-sever x.x.x.x" ... so am just trying to understand how is the DNS processing working ?
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Question by:nabeel92
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6 Comments
 
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Expert Comment

by:Lee W, MVP
ID: 24084752
Your Windows DNS server MAY be configured with forwarders (Forwarder settings).  In which case, any domain name it cannot resolve will have the request forwarded to the server(s) defined in the setting.  However, if there are no forwarders defined, then the resolution request is forwarded to the internet root servers as any other DNS server would.
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Author Comment

by:nabeel92
ID: 24085612
Ok ...I checked in the DNS server (forwarder) and I don't see anything configured .. I've attached 2 snapshots ... From what you mentioned, looks like all our DNS requests are resolved by the internet root servers ?
1.JPG
2.JPG
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Author Comment

by:nabeel92
ID: 24093350
Ok, this is what i noticed today ! I went to this other server which is configured as the secondary DNS server and in its forwarder, i found the ISP's DNS server I.P ...

Now, I have a primary DNS server (that I pasted the snapshots above) and is not configured with ISP's name server so i'm assuming it must be going out to the internet root sever ... The secondary DNS server is configured with ISP's DNS I.P ... So which 1 gets preference ... Are all the clients going via primary DNS (i.e. Internet root server ) or secondary DNS (ISP's DNS) ?

Attached is a snapshot of forwarder tab in my secondary DNS server
1.JPG
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Expert Comment

by:Chris Dent
ID: 24094627

> So which 1 gets preference ... Are all the clients going via primary DNS (i.e. Internet
> root server ) or secondary DNS (ISP's DNS) ?

Which one appears first in their TCP/IP configuration (ipconfig /all)? That one is used first, any later entries only if the first is busy (too slow to respond) or down.

The clients won't know what configuration is in place for the servers to get the answers, they just yell "hey, where is www.google.com?" and wait for a response.

If you're interested, you will find the list of root servers you query under "Root Hints". Those are used to start off the name resolution process, your server has to find it's way down the tree to get to a domain when using Root Hints. e.g.:

- Root knows where .com is
- .com knows where google.com is
- google.com knows where www.google.com is

When using Forwarders your server does what the client just did, yells at the forwarder and waits for an answer.

HTH

Chris
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Author Comment

by:nabeel92
ID: 24094933
so my primary one is basically forwarding to internet root servers ... and its cache is also set to default 1 hour ... wont that yeild poor performance ? if i change it to ISP and then change the cache time out to 24 hours ... ??
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Chris Dent earned 500 total points
ID: 24095687

Which cache time? There's a maximum cache time, but you'd have to set that in the registry. If you haven't changed that everything will cache based on the TTL (Time To Live) of the requested record. Where are you looking?

Changing the server to forward to your ISP will result in a slight increase in performance because your server would only make one query, where three are needed in the resolution of www.google.com above (although most of the data will be in the cache anyway). If you're happy with your ISP there's little reason not to do that, just a matter of whether you trust them or not :)

Chris
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