Root hints with Forwarders?

Do I need to care about my root hint servers if I configure our name servers
to use forwarders?

Hello gscanga,

From another posting:

"Forwarder vs Root Hint"
By configuring a forwarder, you are specifying one or more IPs that your
DNS erver will forward queries to if it cannot resolve a query locally.
When configured with a forwarder, the DNS server will perform a recursive
query; that is, it will forward the query to the forwarder then sit back
and wait for the response. Whatever response is received from the forwarder
is sent back to the client as-is, the DNS server will make no further attempt
to locate the resource if the forwarder cannot resolve it. In the case of
root hints, the DNS server itself will perform an iterative query to locate
the resource, starting at the .com ROOT server, for example, then using referrals
to move to the microsoft.com server and then to the east.microsoft.com server,
so on and so forth until it either receives an authoritative answer or is
unable to resolve the query. The difference here, really, is in -which- DNS
server is performing the work. In the case of a forwarder, your DNS server
is off-loading its name resolution onto another DNS server, most likely your
ISP's server. In the case of root hints, your DNS server is doing all of
the "heavy lifting" itself.
One thing to be aware of when using root hints is to be certain that your
Microsoft DNS server has not configured -itself- as a root hints server.
If you see a DNS zone called '.' in the DNS management console, delete it
so that your server can use the actual Internet root servers successfully.

Best regards

Meinolf Weber
Disclaimer: This posting is provided "AS IS" with no warranties, and confers
no rights.
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> Do I need to care about my root hint servers if I configure our name
> servers to use forwarders?
>

Perfect- thank you, Meinolf.


"Meinolf Weber [MVP-DS]" wrote:

"gscanga" <> wrote in message
news:33AE0322-9900-4F90-AC11-...
> Do I need to care about my root hint servers if I configure our name
> servers
> to use forwarders?

In addition to Meinolf's explanation, it depends on the level of fault
tolerance. But then again, it also depends on the number of forwarders. DNS
acts as a resolving client when it uses a Forwarder because as the
explanation indicated, it is sending the request elsewhere, essentially
offloading the request so it doesn't have to hit the Roots to devolve the
query. If there are multiple Forwarders, DNS will hit each Forwarder. If it
runs out of Forwarders, only then will it use the Roots, unless the checkbox
to disable recursion is set under the Forwarders tab (not the Advanced tab).
But then that all takes time. Keep in mind there is a time out that a client
will wait, so if the original client request that sent it to your DNS server
is waiting beyond the time out period, and the DNS server is waiting on it's
resolution request from a Forwarder, and the time out period is reached and
no response is received, the client will assume that the DNS address that it
used is no good and will remove it from the 'eligible resolvers list' and
then query the second one.

So for all practical purposes, I never set more than two Forwarders,
otherwise what's the use? If the first two can't resolve it, it probably is
not resolvable anyway.

Make sense?

Here's more info and a discussion I previously had with Kevin Goodnecht
concerning this topic and the timeout period:
------

DNS Forwarder Resolution and Time Out Process:

Information on how a DNS Forwarder time-out works with using multiple
Forwarder:

Keep in mind, if you have too many forwarders listed, and only one is
recommended (I believe 6 is the most it will use), the client side resolver
may time out waiting for the 4th forwarder to get queried and will go to the
next DNS server listed in the client's IP properties.

Configure a DNS server to use forwarders (you can change the time-out
period)
http://technet.microsoft.com/en-us/l.../cc773370.aspx

Good explanation by Kevin Goodnecht explaining the forwarders time out and
scenarios with too many Forwarders listed.
http://help.lockergnome.com/windows2...ict482618.html
quoted from above link:
"Actually, the DNS service will stick to the Forwarder that provides an
answer, no matter where it is in the list, if one forwarder times out(no
answer) it will move to the next forwarder in the list, if the next
forwarder provides an answer it uses it until it times out. The problem for
you is, that it may not get back around to the first forwarder, before the
Forwarding timeout expires, and it starts using recursion itself and goes to
the root hints.

Now, if you check the box "Do not use recursion" the DNS server will use
only its forwarders, and will not use root hints. But this cannot guarantee
that one of the other servers being used as a forwarder answer the query,

I recommend that if there is a domain that cannot be reached through the
internet root, that you add a secondary zone for that domain on the Win2k
DNS server."


--
Ace

This posting is provided "AS-IS" with no warranties or guarantees and
confers no rights.

Ace Fekay, MCSE 2003 & 2000, MCSA 2003 & 2000, MCSA Messaging, MCT
Microsoft Certified Trainer


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