DNS + Forwarders


G

Guest

Hey all,

A little unsure about DNS and forwarders could you check to see if my logic
is flawed.

Win 2000 domain, 7 Dcs, 5 around the country and 2 in head office

Under the DNS mmc some of the servers have "Enable Forwarders" ticked and
some don't. The two DCs in head office are the main DNS servers.

Shouldn't all the DNS servers have "Enabled Forwarders" ticked and pointing
back to our main DNS servers? Any reason why they shouldn't?

Shouldn't it be PC -> local DNS server, if this cant resolve it, it should
point it back to the main DNS servers which if again cant resolve then goes
to the root hints. So
PC -> Local DNS -> Main DNS -> Root hints

Hope this makes sense, thanks

Regards
Adrian
 
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G

Guest

Just one other thing

For each DC I have the NIC set up as follows

Preferred DNS Server: local IP address
Alternative DNS Server: Main DNS server

Is this correct/Good practice ?

Thanks Again
 
K

Kurt

If the zones are AD Integrated or even if they're secondaries, no forwarding
to the main site DNS server should be required. You could forward to an ISP
if you feel the local traffic for off-domain queries warrants it, but that's
mostly a local bandwidth issue, whether your server queries a forwarder or
performs the lookup itself, it still uses WAN bandwidth. The only time
forwarding to the main site server might be of value is if you had just
added a new record that needs to be resolved immediately by the remote site,
and you have zone transfers throttled back. But then everytime a local
server can't find a record, it'll forward the request to the main site,
which will also not be able to resolve it 99.9999% of the time, so an
unnecessary waste of bandwidth.

....kurt
 
H

Herb Martin

Adrian said:
Hey all,

A little unsure about DNS and forwarders could you check to see if my
logic
is flawed.

Win 2000 domain, 7 Dcs, 5 around the country and 2 in head office

Under the DNS mmc some of the servers have "Enable Forwarders" ticked and
some don't. The two DCs in head office are the main DNS servers.

Why do you enable Forwarders?

If the answer is that your DNS servers don't hold ALL of your
internal zone, or that you wish to resolve THE Internet then
likely EVER DNS server should enable forwarders if any of
them do.

There are two general ways for a DNS server to resolve names it doesn't
'know directly' (i.e., for zones it doesn't hold):

1) Recurse physically (root down)
2) Forward

Theorectically some of your DNS servers might be recursing
and others might forward but why would they be different?
Shouldn't all the DNS servers have "Enabled Forwarders" ticked and
pointing
back to our main DNS servers? Any reason why they shouldn't?

You don't want your fowarding chains to be TOO long but this
might make perfect sense if your WAN lines are fairly slow since
your branch DNS will only make ONE forwarding request to the
"Main DNS" which may have the answer in cache (since other
DNS servers and it's direct clients may recently have asked the
same question) OR it will make all of the subsequent requests
(either forward or recursing) for the name and likely be "closer"
to the Internet.

If every branch had its own direct connection to The Internet then
this might not be so helpful.
Shouldn't it be PC -> local DNS server, if this cant resolve it, it should
point it back to the main DNS servers which if again cant resolve then
goes
to the root hints.
So PC -> Local DNS -> Main DNS -> Root hints

That can work, but without a full reading of (and perhaps testing
on) your actual WAN lines we cannot say for sure.
Hope this makes sense, thanks

How does it work currently?
 
G

Guest

Thanks Herb for your detailed response.

Our 7 servers are all "Active Directory Integrated Zones"

Unfortunaly I don't know why some of the servers have "enable forwarders"
ticked and others dont, Ive only recently moved to this firm so Im trying to
make sense how/why it was setup this way.

All the sites are connected to the internet through our proxy server at head
office, the WAN links are all quite good running at 512 -1Mb on dedicated
lines so I dont think its a bandwidth issue.

All the sites have the exact same hardware and should be identical to each
other configuration wise but some where along the lines someone has made
changes so now I trying to get them all back looking the same again.

How do you think we should be setup in terms if best practice?

Herb Martin said:
Adrian said:
Hey all,

A little unsure about DNS and forwarders could you check to see if my
logic
is flawed.

Win 2000 domain, 7 Dcs, 5 around the country and 2 in head office

Under the DNS mmc some of the servers have "Enable Forwarders" ticked and
some don't. The two DCs in head office are the main DNS servers.

Why do you enable Forwarders?

If the answer is that your DNS servers don't hold ALL of your
internal zone, or that you wish to resolve THE Internet then
likely EVER DNS server should enable forwarders if any of
them do.

There are two general ways for a DNS server to resolve names it doesn't
'know directly' (i.e., for zones it doesn't hold):

1) Recurse physically (root down)
2) Forward

Theorectically some of your DNS servers might be recursing
and others might forward but why would they be different?
Shouldn't all the DNS servers have "Enabled Forwarders" ticked and
pointing
back to our main DNS servers? Any reason why they shouldn't?

You don't want your fowarding chains to be TOO long but this
might make perfect sense if your WAN lines are fairly slow since
your branch DNS will only make ONE forwarding request to the
"Main DNS" which may have the answer in cache (since other
DNS servers and it's direct clients may recently have asked the
same question) OR it will make all of the subsequent requests
(either forward or recursing) for the name and likely be "closer"
to the Internet.

If every branch had its own direct connection to The Internet then
this might not be so helpful.
Shouldn't it be PC -> local DNS server, if this cant resolve it, it should
point it back to the main DNS servers which if again cant resolve then
goes
to the root hints.
So PC -> Local DNS -> Main DNS -> Root hints

That can work, but without a full reading of (and perhaps testing
on) your actual WAN lines we cannot say for sure.
Hope this makes sense, thanks

How does it work currently?

--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]

Regards
Adrian
 
K

Kurt

ADI zones, if all servers hold all the same zones, should be identical.
Every site with a local Internet connection could have a forwarder to the
local ISP's DNS server. As Herb pointed out, it MIGHT have some value to
forward from a site that doesn't have it's own internet service to a DNS
server in a site that does, so that only one forward query and one reply
will traverse the WAN, and further forward queries or recursive lookups are
performed from a site with a separate Internet connection to conserver WAN
bandwidth. I see no point in having both. Herb?

....kurt


Adrian said:
Thanks Herb for your detailed response.

Our 7 servers are all "Active Directory Integrated Zones"

Unfortunaly I don't know why some of the servers have "enable forwarders"
ticked and others dont, Ive only recently moved to this firm so Im trying
to
make sense how/why it was setup this way.

All the sites are connected to the internet through our proxy server at
head
office, the WAN links are all quite good running at 512 -1Mb on dedicated
lines so I dont think its a bandwidth issue.

All the sites have the exact same hardware and should be identical to each
other configuration wise but some where along the lines someone has made
changes so now I trying to get them all back looking the same again.

How do you think we should be setup in terms if best practice?

Herb Martin said:
Adrian said:
Hey all,

A little unsure about DNS and forwarders could you check to see if my
logic
is flawed.

Win 2000 domain, 7 Dcs, 5 around the country and 2 in head office

Under the DNS mmc some of the servers have "Enable Forwarders" ticked
and
some don't. The two DCs in head office are the main DNS servers.

Why do you enable Forwarders?

If the answer is that your DNS servers don't hold ALL of your
internal zone, or that you wish to resolve THE Internet then
likely EVER DNS server should enable forwarders if any of
them do.

There are two general ways for a DNS server to resolve names it doesn't
'know directly' (i.e., for zones it doesn't hold):

1) Recurse physically (root down)
2) Forward

Theorectically some of your DNS servers might be recursing
and others might forward but why would they be different?
Shouldn't all the DNS servers have "Enabled Forwarders" ticked and
pointing
back to our main DNS servers? Any reason why they shouldn't?

You don't want your fowarding chains to be TOO long but this
might make perfect sense if your WAN lines are fairly slow since
your branch DNS will only make ONE forwarding request to the
"Main DNS" which may have the answer in cache (since other
DNS servers and it's direct clients may recently have asked the
same question) OR it will make all of the subsequent requests
(either forward or recursing) for the name and likely be "closer"
to the Internet.

If every branch had its own direct connection to The Internet then
this might not be so helpful.
Shouldn't it be PC -> local DNS server, if this cant resolve it, it
should
point it back to the main DNS servers which if again cant resolve then
goes
to the root hints.
So PC -> Local DNS -> Main DNS -> Root hints

That can work, but without a full reading of (and perhaps testing
on) your actual WAN lines we cannot say for sure.
Hope this makes sense, thanks

How does it work currently?

--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]

Regards
Adrian
 
Ad

Advertisements

H

Herb Martin

Kurt said:
ADI zones, if all servers hold all the same zones, should be identical.

Forwarder setting is however NOT a zone setting so
he can easily set different servers to different forwarding
options.
Every site with a local Internet connection could have a forwarder to the
local ISP's DNS server. As Herb pointed out, it MIGHT have some value to
forward from a site that doesn't have it's own internet service to a DNS
server in a site that does, so that only one forward query and one reply
will traverse the WAN, and further forward queries or recursive lookups
are performed from a site with a separate Internet connection to conserver
WAN bandwidth. I see no point in having both. Herb?

Of course you are correct that he should use AD Integrated
DNS for all of his own zones. (Unless compelling reasons
suggest otherwise, e.g., no DC but need another DNS for
fault tolerance etc) this is always our first choice for our
Microsoft domain DNS.

As to forwarders I agree again.

Generally it is a NICE IDEA to have ONLY ONE DNS server
(or set) at the FIREWALL/DMZ/Gateway to the Internet which
does ALL of the public lookups.

Two reasons for this: I don't want those DC-DNS servers out
on the Internet AT ALL, especially not recursing to places like
EvilHackersRUs.com <grin>.

And, by doing this we consolidate cache for every other DNS
server that forwarders there so we get more cache successes
without even crossing the WAN to the Internet or ISP.

As to branch offices, if there can forward to that "gatewayDMZ"
DNS directly that is usually there best choice since we now
avoid adding multiple forwarder chains (which may work but
eventually become excessive -- testing required.)

So the actual forwarder should (generally) NOT be an AD-DNS
but might just be a feature of your hardware routers/firewalls.

(This DNS holds NO zones, in a perfect world, and would have
nothing to do with resolving YOUR resources for people on
the Internet. Properly that job is done by SEPARATE DNS
servers and for most companies is best left at the REGISTRAR.)


--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]
...kurt


Adrian said:
Thanks Herb for your detailed response.

Our 7 servers are all "Active Directory Integrated Zones"

Unfortunaly I don't know why some of the servers have "enable forwarders"
ticked and others dont, Ive only recently moved to this firm so Im trying
to
make sense how/why it was setup this way.

All the sites are connected to the internet through our proxy server at
head
office, the WAN links are all quite good running at 512 -1Mb on dedicated
lines so I dont think its a bandwidth issue.

All the sites have the exact same hardware and should be identical to
each
other configuration wise but some where along the lines someone has made
changes so now I trying to get them all back looking the same again.

How do you think we should be setup in terms if best practice?

Herb Martin said:
Hey all,

A little unsure about DNS and forwarders could you check to see if my
logic
is flawed.

Win 2000 domain, 7 Dcs, 5 around the country and 2 in head office

Under the DNS mmc some of the servers have "Enable Forwarders" ticked
and
some don't. The two DCs in head office are the main DNS servers.

Why do you enable Forwarders?

If the answer is that your DNS servers don't hold ALL of your
internal zone, or that you wish to resolve THE Internet then
likely EVER DNS server should enable forwarders if any of
them do.

There are two general ways for a DNS server to resolve names it doesn't
'know directly' (i.e., for zones it doesn't hold):

1) Recurse physically (root down)
2) Forward

Theorectically some of your DNS servers might be recursing
and others might forward but why would they be different?

Shouldn't all the DNS servers have "Enabled Forwarders" ticked and
pointing
back to our main DNS servers? Any reason why they shouldn't?

You don't want your fowarding chains to be TOO long but this
might make perfect sense if your WAN lines are fairly slow since
your branch DNS will only make ONE forwarding request to the
"Main DNS" which may have the answer in cache (since other
DNS servers and it's direct clients may recently have asked the
same question) OR it will make all of the subsequent requests
(either forward or recursing) for the name and likely be "closer"
to the Internet.

If every branch had its own direct connection to The Internet then
this might not be so helpful.

Shouldn't it be PC -> local DNS server, if this cant resolve it, it
should
point it back to the main DNS servers which if again cant resolve then
goes
to the root hints.
So PC -> Local DNS -> Main DNS -> Root hints

That can work, but without a full reading of (and perhaps testing
on) your actual WAN lines we cannot say for sure.

Hope this makes sense, thanks

How does it work currently?

--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]


Regards
Adrian
 
K

Kurt

Right, that's why I qualified it with "if all the servers hold the same
zones". I'm probably assuming too much here, but I gathered from the OP's
reference to the singular "domain" rather than "domains" probably means
there is only one authoritative zone, and since he confirmed that it is ADI
that all DNS servers would have a copy.

....kurt


Herb Martin said:
Kurt said:
ADI zones, if all servers hold all the same zones, should be identical.

Forwarder setting is however NOT a zone setting so
he can easily set different servers to different forwarding
options.
Every site with a local Internet connection could have a forwarder to the
local ISP's DNS server. As Herb pointed out, it MIGHT have some value to
forward from a site that doesn't have it's own internet service to a DNS
server in a site that does, so that only one forward query and one reply
will traverse the WAN, and further forward queries or recursive lookups
are performed from a site with a separate Internet connection to
conserver WAN bandwidth. I see no point in having both. Herb?

Of course you are correct that he should use AD Integrated
DNS for all of his own zones. (Unless compelling reasons
suggest otherwise, e.g., no DC but need another DNS for
fault tolerance etc) this is always our first choice for our
Microsoft domain DNS.

As to forwarders I agree again.

Generally it is a NICE IDEA to have ONLY ONE DNS server
(or set) at the FIREWALL/DMZ/Gateway to the Internet which
does ALL of the public lookups.

Two reasons for this: I don't want those DC-DNS servers out
on the Internet AT ALL, especially not recursing to places like
EvilHackersRUs.com <grin>.

And, by doing this we consolidate cache for every other DNS
server that forwarders there so we get more cache successes
without even crossing the WAN to the Internet or ISP.

As to branch offices, if there can forward to that "gatewayDMZ"
DNS directly that is usually there best choice since we now
avoid adding multiple forwarder chains (which may work but
eventually become excessive -- testing required.)

So the actual forwarder should (generally) NOT be an AD-DNS
but might just be a feature of your hardware routers/firewalls.

(This DNS holds NO zones, in a perfect world, and would have
nothing to do with resolving YOUR resources for people on
the Internet. Properly that job is done by SEPARATE DNS
servers and for most companies is best left at the REGISTRAR.)


--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]
...kurt


Adrian said:
Thanks Herb for your detailed response.

Our 7 servers are all "Active Directory Integrated Zones"

Unfortunaly I don't know why some of the servers have "enable
forwarders"
ticked and others dont, Ive only recently moved to this firm so Im
trying to
make sense how/why it was setup this way.

All the sites are connected to the internet through our proxy server at
head
office, the WAN links are all quite good running at 512 -1Mb on
dedicated
lines so I dont think its a bandwidth issue.

All the sites have the exact same hardware and should be identical to
each
other configuration wise but some where along the lines someone has made
changes so now I trying to get them all back looking the same again.

How do you think we should be setup in terms if best practice?

:

Hey all,

A little unsure about DNS and forwarders could you check to see if my
logic
is flawed.

Win 2000 domain, 7 Dcs, 5 around the country and 2 in head office

Under the DNS mmc some of the servers have "Enable Forwarders" ticked
and
some don't. The two DCs in head office are the main DNS servers.

Why do you enable Forwarders?

If the answer is that your DNS servers don't hold ALL of your
internal zone, or that you wish to resolve THE Internet then
likely EVER DNS server should enable forwarders if any of
them do.

There are two general ways for a DNS server to resolve names it doesn't
'know directly' (i.e., for zones it doesn't hold):

1) Recurse physically (root down)
2) Forward

Theorectically some of your DNS servers might be recursing
and others might forward but why would they be different?

Shouldn't all the DNS servers have "Enabled Forwarders" ticked and
pointing
back to our main DNS servers? Any reason why they shouldn't?

You don't want your fowarding chains to be TOO long but this
might make perfect sense if your WAN lines are fairly slow since
your branch DNS will only make ONE forwarding request to the
"Main DNS" which may have the answer in cache (since other
DNS servers and it's direct clients may recently have asked the
same question) OR it will make all of the subsequent requests
(either forward or recursing) for the name and likely be "closer"
to the Internet.

If every branch had its own direct connection to The Internet then
this might not be so helpful.

Shouldn't it be PC -> local DNS server, if this cant resolve it, it
should
point it back to the main DNS servers which if again cant resolve
then
goes
to the root hints.
So PC -> Local DNS -> Main DNS -> Root hints

That can work, but without a full reading of (and perhaps testing
on) your actual WAN lines we cannot say for sure.

Hope this makes sense, thanks

How does it work currently?

--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]


Regards
Adrian
 
H

Herb Martin

Kurt said:
Right, that's why I qualified it with "if all the servers hold the same
zones". I'm probably assuming too much here, but I gathered from the OP's
reference to the singular "domain" rather than "domains" probably means
there is only one authoritative zone, and since he confirmed that it is
ADI that all DNS servers would have a copy.

That was implied (if never stated explicitly) and I was in
no way disagreeing with or correcting you, just elaborating.

Ultimately we would need to get full particulars and perhaps
test to give him a an EASY "best answer" rather than good
-- and very explicit -- design principles that will teach how
to solve most any similar problem.

--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]
...kurt


Herb Martin said:
Kurt said:
ADI zones, if all servers hold all the same zones, should be identical.

Forwarder setting is however NOT a zone setting so
he can easily set different servers to different forwarding
options.
Every site with a local Internet connection could have a forwarder to
the local ISP's DNS server. As Herb pointed out, it MIGHT have some
value to forward from a site that doesn't have it's own internet service
to a DNS server in a site that does, so that only one forward query and
one reply will traverse the WAN, and further forward queries or
recursive lookups are performed from a site with a separate Internet
connection to conserver WAN bandwidth. I see no point in having both.
Herb?

Of course you are correct that he should use AD Integrated
DNS for all of his own zones. (Unless compelling reasons
suggest otherwise, e.g., no DC but need another DNS for
fault tolerance etc) this is always our first choice for our
Microsoft domain DNS.

As to forwarders I agree again.

Generally it is a NICE IDEA to have ONLY ONE DNS server
(or set) at the FIREWALL/DMZ/Gateway to the Internet which
does ALL of the public lookups.

Two reasons for this: I don't want those DC-DNS servers out
on the Internet AT ALL, especially not recursing to places like
EvilHackersRUs.com <grin>.

And, by doing this we consolidate cache for every other DNS
server that forwarders there so we get more cache successes
without even crossing the WAN to the Internet or ISP.

As to branch offices, if there can forward to that "gatewayDMZ"
DNS directly that is usually there best choice since we now
avoid adding multiple forwarder chains (which may work but
eventually become excessive -- testing required.)

So the actual forwarder should (generally) NOT be an AD-DNS
but might just be a feature of your hardware routers/firewalls.

(This DNS holds NO zones, in a perfect world, and would have
nothing to do with resolving YOUR resources for people on
the Internet. Properly that job is done by SEPARATE DNS
servers and for most companies is best left at the REGISTRAR.)


--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]
...kurt


Thanks Herb for your detailed response.

Our 7 servers are all "Active Directory Integrated Zones"

Unfortunaly I don't know why some of the servers have "enable
forwarders"
ticked and others dont, Ive only recently moved to this firm so Im
trying to
make sense how/why it was setup this way.

All the sites are connected to the internet through our proxy server at
head
office, the WAN links are all quite good running at 512 -1Mb on
dedicated
lines so I dont think its a bandwidth issue.

All the sites have the exact same hardware and should be identical to
each
other configuration wise but some where along the lines someone has
made
changes so now I trying to get them all back looking the same again.

How do you think we should be setup in terms if best practice?

:

Hey all,

A little unsure about DNS and forwarders could you check to see if
my
logic
is flawed.

Win 2000 domain, 7 Dcs, 5 around the country and 2 in head office

Under the DNS mmc some of the servers have "Enable Forwarders"
ticked and
some don't. The two DCs in head office are the main DNS servers.

Why do you enable Forwarders?

If the answer is that your DNS servers don't hold ALL of your
internal zone, or that you wish to resolve THE Internet then
likely EVER DNS server should enable forwarders if any of
them do.

There are two general ways for a DNS server to resolve names it
doesn't
'know directly' (i.e., for zones it doesn't hold):

1) Recurse physically (root down)
2) Forward

Theorectically some of your DNS servers might be recursing
and others might forward but why would they be different?

Shouldn't all the DNS servers have "Enabled Forwarders" ticked and
pointing
back to our main DNS servers? Any reason why they shouldn't?

You don't want your fowarding chains to be TOO long but this
might make perfect sense if your WAN lines are fairly slow since
your branch DNS will only make ONE forwarding request to the
"Main DNS" which may have the answer in cache (since other
DNS servers and it's direct clients may recently have asked the
same question) OR it will make all of the subsequent requests
(either forward or recursing) for the name and likely be "closer"
to the Internet.

If every branch had its own direct connection to The Internet then
this might not be so helpful.

Shouldn't it be PC -> local DNS server, if this cant resolve it, it
should
point it back to the main DNS servers which if again cant resolve
then
goes
to the root hints.
So PC -> Local DNS -> Main DNS -> Root hints

That can work, but without a full reading of (and perhaps testing
on) your actual WAN lines we cannot say for sure.

Hope this makes sense, thanks

How does it work currently?

--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]


Regards
Adrian
 
G

Guest

Wow thanks again for the detailed response guys.

I have to admit through that some of it is going a little over myhead, Im
quite new to this, but thats ok I like to learn.

I going to do a little more research on the MS site and hopefully then I
will be better able to answer your Questions because I think that this is
obviously something which you need to learn how to do correctly.
Ultimately we would need to get full particulars and perhaps
test to give him a an EASY "best answer" rather than good
-- and very explicit -- design principles that will teach how
to solve most any similar problem.

This would probably help alot, I can run any test you think might help.



Herb Martin said:
Kurt said:
Right, that's why I qualified it with "if all the servers hold the same
zones". I'm probably assuming too much here, but I gathered from the OP's
reference to the singular "domain" rather than "domains" probably means
there is only one authoritative zone, and since he confirmed that it is
ADI that all DNS servers would have a copy.

That was implied (if never stated explicitly) and I was in
no way disagreeing with or correcting you, just elaborating.

Ultimately we would need to get full particulars and perhaps
test to give him a an EASY "best answer" rather than good
-- and very explicit -- design principles that will teach how
to solve most any similar problem.

--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]
...kurt


Herb Martin said:
ADI zones, if all servers hold all the same zones, should be identical.

Forwarder setting is however NOT a zone setting so
he can easily set different servers to different forwarding
options.

Every site with a local Internet connection could have a forwarder to
the local ISP's DNS server. As Herb pointed out, it MIGHT have some
value to forward from a site that doesn't have it's own internet service
to a DNS server in a site that does, so that only one forward query and
one reply will traverse the WAN, and further forward queries or
recursive lookups are performed from a site with a separate Internet
connection to conserver WAN bandwidth. I see no point in having both.
Herb?

Of course you are correct that he should use AD Integrated
DNS for all of his own zones. (Unless compelling reasons
suggest otherwise, e.g., no DC but need another DNS for
fault tolerance etc) this is always our first choice for our
Microsoft domain DNS.

As to forwarders I agree again.

Generally it is a NICE IDEA to have ONLY ONE DNS server
(or set) at the FIREWALL/DMZ/Gateway to the Internet which
does ALL of the public lookups.

Two reasons for this: I don't want those DC-DNS servers out
on the Internet AT ALL, especially not recursing to places like
EvilHackersRUs.com <grin>.

And, by doing this we consolidate cache for every other DNS
server that forwarders there so we get more cache successes
without even crossing the WAN to the Internet or ISP.

As to branch offices, if there can forward to that "gatewayDMZ"
DNS directly that is usually there best choice since we now
avoid adding multiple forwarder chains (which may work but
eventually become excessive -- testing required.)

So the actual forwarder should (generally) NOT be an AD-DNS
but might just be a feature of your hardware routers/firewalls.

(This DNS holds NO zones, in a perfect world, and would have
nothing to do with resolving YOUR resources for people on
the Internet. Properly that job is done by SEPARATE DNS
servers and for most companies is best left at the REGISTRAR.)


--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]


...kurt


Thanks Herb for your detailed response.

Our 7 servers are all "Active Directory Integrated Zones"

Unfortunaly I don't know why some of the servers have "enable
forwarders"
ticked and others dont, Ive only recently moved to this firm so Im
trying to
make sense how/why it was setup this way.

All the sites are connected to the internet through our proxy server at
head
office, the WAN links are all quite good running at 512 -1Mb on
dedicated
lines so I dont think its a bandwidth issue.

All the sites have the exact same hardware and should be identical to
each
other configuration wise but some where along the lines someone has
made
changes so now I trying to get them all back looking the same again.

How do you think we should be setup in terms if best practice?

:

Hey all,

A little unsure about DNS and forwarders could you check to see if
my
logic
is flawed.

Win 2000 domain, 7 Dcs, 5 around the country and 2 in head office

Under the DNS mmc some of the servers have "Enable Forwarders"
ticked and
some don't. The two DCs in head office are the main DNS servers.

Why do you enable Forwarders?

If the answer is that your DNS servers don't hold ALL of your
internal zone, or that you wish to resolve THE Internet then
likely EVER DNS server should enable forwarders if any of
them do.

There are two general ways for a DNS server to resolve names it
doesn't
'know directly' (i.e., for zones it doesn't hold):

1) Recurse physically (root down)
2) Forward

Theorectically some of your DNS servers might be recursing
and others might forward but why would they be different?

Shouldn't all the DNS servers have "Enabled Forwarders" ticked and
pointing
back to our main DNS servers? Any reason why they shouldn't?

You don't want your fowarding chains to be TOO long but this
might make perfect sense if your WAN lines are fairly slow since
your branch DNS will only make ONE forwarding request to the
"Main DNS" which may have the answer in cache (since other
DNS servers and it's direct clients may recently have asked the
same question) OR it will make all of the subsequent requests
(either forward or recursing) for the name and likely be "closer"
to the Internet.

If every branch had its own direct connection to The Internet then
this might not be so helpful.

Shouldn't it be PC -> local DNS server, if this cant resolve it, it
should
point it back to the main DNS servers which if again cant resolve
then
goes
to the root hints.
So PC -> Local DNS -> Main DNS -> Root hints

That can work, but without a full reading of (and perhaps testing
on) your actual WAN lines we cannot say for sure.

Hope this makes sense, thanks

How does it work currently?

--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]


Regards
Adrian
 
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H

Herb Martin

Adrian said:
Wow thanks again for the detailed response guys.

You are certainly welcome.
I have to admit through that some of it is going a little over myhead, Im
quite new to this, but thats ok I like to learn.

Then you might wish to quote the message (or pertinent sections)
and ask your questions (or better state your understanding) for each
significant point that seems to be unclear to you.....
I going to do a little more research on the MS site and hopefully then I
will be better able to answer your Questions because I think that this is
obviously something which you need to learn how to do correctly.

You would probably get faster answers and learn both better and
faster if you just tried the response technique above rather than
read a lot of (unfocused) sources.

Frequently we can point you right to your misunderstandings or
help you to focus on the KEY points you have not yet learned.
This would probably help alot, I can run any test you think might help.

Actually, I am strongly suggesting you would benefit more by
understanding those design principles yourself, and then you
could run your own tests as necessary.

We aren't there where we can "see your stuff" so trying to actually
OPTIMIZE a system is a bit difficult remotely. (I have a reputation
-- good or bad <grin> -- as an optimization specialist but yet I
will tell you straight out it is a "black art" not a science even though
one must actually PERFORM each such analysis in a scientific and
rigorous fashion: first measuring current response, guessing an
improvement, and then performing anther measurement and tests
to determine the improvement AND to feed the next guess for another
change.)

Optimization without measurement is like gambling in a crooked game:
You aren't likely to win anyway, but even if you do your winnings
will be stolen. (Really)


--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]
Herb Martin said:
Kurt said:
Right, that's why I qualified it with "if all the servers hold the same
zones". I'm probably assuming too much here, but I gathered from the
OP's
reference to the singular "domain" rather than "domains" probably means
there is only one authoritative zone, and since he confirmed that it is
ADI that all DNS servers would have a copy.

That was implied (if never stated explicitly) and I was in
no way disagreeing with or correcting you, just elaborating.

Ultimately we would need to get full particulars and perhaps
test to give him a an EASY "best answer" rather than good
-- and very explicit -- design principles that will teach how
to solve most any similar problem.

--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]
...kurt


ADI zones, if all servers hold all the same zones, should be
identical.

Forwarder setting is however NOT a zone setting so
he can easily set different servers to different forwarding
options.

Every site with a local Internet connection could have a forwarder to
the local ISP's DNS server. As Herb pointed out, it MIGHT have some
value to forward from a site that doesn't have it's own internet
service
to a DNS server in a site that does, so that only one forward query
and
one reply will traverse the WAN, and further forward queries or
recursive lookups are performed from a site with a separate Internet
connection to conserver WAN bandwidth. I see no point in having both.
Herb?

Of course you are correct that he should use AD Integrated
DNS for all of his own zones. (Unless compelling reasons
suggest otherwise, e.g., no DC but need another DNS for
fault tolerance etc) this is always our first choice for our
Microsoft domain DNS.

As to forwarders I agree again.

Generally it is a NICE IDEA to have ONLY ONE DNS server
(or set) at the FIREWALL/DMZ/Gateway to the Internet which
does ALL of the public lookups.

Two reasons for this: I don't want those DC-DNS servers out
on the Internet AT ALL, especially not recursing to places like
EvilHackersRUs.com <grin>.

And, by doing this we consolidate cache for every other DNS
server that forwarders there so we get more cache successes
without even crossing the WAN to the Internet or ISP.

As to branch offices, if there can forward to that "gatewayDMZ"
DNS directly that is usually there best choice since we now
avoid adding multiple forwarder chains (which may work but
eventually become excessive -- testing required.)

So the actual forwarder should (generally) NOT be an AD-DNS
but might just be a feature of your hardware routers/firewalls.

(This DNS holds NO zones, in a perfect world, and would have
nothing to do with resolving YOUR resources for people on
the Internet. Properly that job is done by SEPARATE DNS
servers and for most companies is best left at the REGISTRAR.)


--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]


...kurt


Thanks Herb for your detailed response.

Our 7 servers are all "Active Directory Integrated Zones"

Unfortunaly I don't know why some of the servers have "enable
forwarders"
ticked and others dont, Ive only recently moved to this firm so Im
trying to
make sense how/why it was setup this way.

All the sites are connected to the internet through our proxy server
at
head
office, the WAN links are all quite good running at 512 -1Mb on
dedicated
lines so I dont think its a bandwidth issue.

All the sites have the exact same hardware and should be identical
to
each
other configuration wise but some where along the lines someone has
made
changes so now I trying to get them all back looking the same again.

How do you think we should be setup in terms if best practice?

:

Hey all,

A little unsure about DNS and forwarders could you check to see
if
my
logic
is flawed.

Win 2000 domain, 7 Dcs, 5 around the country and 2 in head office

Under the DNS mmc some of the servers have "Enable Forwarders"
ticked and
some don't. The two DCs in head office are the main DNS servers.

Why do you enable Forwarders?

If the answer is that your DNS servers don't hold ALL of your
internal zone, or that you wish to resolve THE Internet then
likely EVER DNS server should enable forwarders if any of
them do.

There are two general ways for a DNS server to resolve names it
doesn't
'know directly' (i.e., for zones it doesn't hold):

1) Recurse physically (root down)
2) Forward

Theorectically some of your DNS servers might be recursing
and others might forward but why would they be different?

Shouldn't all the DNS servers have "Enabled Forwarders" ticked
and
pointing
back to our main DNS servers? Any reason why they shouldn't?

You don't want your fowarding chains to be TOO long but this
might make perfect sense if your WAN lines are fairly slow since
your branch DNS will only make ONE forwarding request to the
"Main DNS" which may have the answer in cache (since other
DNS servers and it's direct clients may recently have asked the
same question) OR it will make all of the subsequent requests
(either forward or recursing) for the name and likely be "closer"
to the Internet.

If every branch had its own direct connection to The Internet then
this might not be so helpful.

Shouldn't it be PC -> local DNS server, if this cant resolve it,
it
should
point it back to the main DNS servers which if again cant resolve
then
goes
to the root hints.
So PC -> Local DNS -> Main DNS -> Root hints

That can work, but without a full reading of (and perhaps testing
on) your actual WAN lines we cannot say for sure.

Hope this makes sense, thanks

How does it work currently?

--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]


Regards
Adrian
 
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