new with dns

[roYal]

Hi, i'm just starting on 70-215, but i signed up here just to get an early
start on learning dns once i finish my 215. I hear people say, add your
isps dns ip to your dns fowarders. I thought once you setup dns, it
automatically stores information about the root servers. So what's the
point of setting up a forwarder to your isps dns if the dns holds info about
the root servers already?

 

[Herb Martin]

Hi, i'm just starting on 70-215, but i signed up here just to get an early
start on learning dns once i finish my 215. I hear people say, add your
isps dns ip to your dns fowarders. I thought once you setup dns, it
automatically stores information about the root servers.

It does -- it's a choice and you can even use both methods.

Normally you don't want your internal servers visiting all the
deep, dark corner of the Internet (it's a cruel world out there)
and the ISP probably has more entries cached (due to other
customers), especially if it's a BIG ISP like RoadRunner or
SWB or UUNET, etc.

So what's the
point of setting up a forwarder to your isps dns if the dns holds info about
the root servers already?

It's a choice -- and sometimes a matter of style. Usually it comes down
to speed, and network efficiency. Those ISP servers are (hopefully)
close to the backbone, across the WAN and have a bigger (more fully
populated) cache.

If they are unreliable, e.g., PoDunkISP.com, then you don't want to use
them at all -- do you own explicit recursion from the top down.

Both methods work -- when you choose a forwarder in MS DNS you
even get another choice to leave explicit recurion active, or check to
"Disable Recursion".

BTW, you are doing find to notice this distinction.