DNS not resolving in a Windows 2003 SP2 network

Hope I am posting this in the correct catagory and that you folks can help
clear the confusion. I have 2 DCs in my network, DC1 & DC2 with the FSMOs
spead out over both DCs - forest MOs on DC1 and domain MOs on DC2. These are
also my 2 DNS servers and the are both Catalog servers. I also have a DHCP
server on DC1 for my client workstations. All my servers are manually
configured with static IPs. I had DC1 freeze on me the other day and all
network funtionalities came to a crashing halt - outlook could not find
Exchange, no browsing, no VPN from outside, internet worked fine if you by
IP address but not by resolving names . Luckly this happened after business
hours so the mayority of users where oblivious to the outage. My confusion
is that if I have 2 DCs also functioning as DNS with zone tranfers functional
and up to date, why did'nt DC2 just take over automatically? My DHCP server
has both DNS servers listed in it by IP - DC1 first then DC2. Can someone
explain this process in laymans terms?

Hello Andy3691,

There is no automatic failover for DNS as you and many other people think
when two DNS servers are in the domain and all machines are configured to
use both of them.

During startup the computers try to contact preferred DNS on the NIC, if
this works it is "stored" locally and the secondary DNS server will be ignored
for further requests, internet or outlook in your case. So if then the preferred
one fails it still tries to use it. A reboot of the machine can resolve this
problem, as during startup it will try to contact a DNS server and if the
preferred doesn't react it choose the secondary.

Best regards

Meinolf Weber
Disclaimer: This posting is provided "AS IS" with no warranties, and confers
no rights.
** Please do NOT email, only reply to Newsgroups
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> Hope I am posting this in the correct catagory and that you folks can
> help clear the confusion. I have 2 DCs in my network, DC1 & DC2 with
> the FSMOs spead out over both DCs - forest MOs on DC1 and domain MOs
> on DC2. These are also my 2 DNS servers and the are both Catalog
> servers. I also have a DHCP server on DC1 for my client workstations.
> All my servers are manually configured with static IPs. I had DC1
> freeze on me the other day and all network funtionalities came to a
> crashing halt - outlook could not find Exchange, no browsing, no VPN
> from outside, internet worked fine if you by IP address but not by
> resolving names . Luckly this happened after business hours so the
> mayority of users where oblivious to the outage. My confusion is that
> if I have 2 DCs also functioning as DNS with zone tranfers functional
> and up to date, why did'nt DC2 just take over automatically? My DHCP
> server has both DNS servers listed in it by IP - DC1 first then DC2.
> Can someone explain this process in laymans terms?
>

"Andy3691" <> wrote in message
news:9E95A106-23D4-4238-A49D-...
> Hope I am posting this in the correct catagory and that you folks can help
> clear the confusion. I have 2 DCs in my network, DC1 & DC2 with the FSMOs
> spead out over both DCs - forest MOs on DC1 and domain MOs on DC2. These
> are
> also my 2 DNS servers and the are both Catalog servers. I also have a
> DHCP
> server on DC1 for my client workstations. All my servers are manually
> configured with static IPs. I had DC1 freeze on me the other day and all
> network funtionalities came to a crashing halt - outlook could not find
> Exchange, no browsing, no VPN from outside, internet worked fine if you
> by
> IP address but not by resolving names . Luckly this happened after
> business
> hours so the mayority of users where oblivious to the outage. My
> confusion
> is that if I have 2 DCs also functioning as DNS with zone tranfers
> functional
> and up to date, why did'nt DC2 just take over automatically? My DHCP
> server
> has both DNS servers listed in it by IP - DC1 first then DC2. Can
> someone
> explain this process in laymans terms?


Good question. This question has been asked numerous times. It's not the
actual DNS server that "takes" over, rather it is a client-side function.
It's based on the client-side resolver algorith. Once a client has resolved
a query (such as to the DC, the Exchange server, or an internet address),
the client-side resolver will keep the answer in it's local cache for the
TTL (time to live) of the record. The TTL of a record is set on the record
in DNS, so the client can't change that. Therefore if one DNS goes down, and
the client already has that server cached in it's record and tries to
communicate to it (such as Outlook, etc), it won't query the other one.

Read up on it in more detail in my blog:

DNS, WINS & the Client Side Resolver, NetBIOS, Browser Service, Disabling
NetBIOS, Direct Hosted SMB (DirectSMB), If One DC is Down, Does a Client
logon to Another DC, and DNS Forwarders Algorithm
http://msmvps.com/blogs/acefekay/arc...algorithm.aspx

If Exchange is on a DC, no need telling you that if you search on it, you
will find numerous topics by many engineers (including Microsoft) stating
Exchange is not recommended to be installed on a domain controller.
Exchange's database transactional logging system is different than AD's.
Once a machine is promoted to a DC, it disabled the write-behind cache
function on the controller. Exchange needs this, however it's done to allow
AD's database system properly work. A huge drawback of this scenario is that
it can cause Exchange to lose emails during certain scenarios, as well as
with the write-behind cache disabled, it drastically reduces performance on
the machine.

Exchange by default, will also consume all memory resources, for example,
the store.exe process and will drag down the OS it is installed on. If the
OS is a DC, it will hinder DC processes, such as the DC's Lsas.exe process.
This *may* result in other issues, possibly with replication.

Read more on it:
This Exchange server is also a domain controller, which is not a recommended
configuration
http://technet.microsoft.com/en-us/l.../aa997407.aspx

--
Ace

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

Please reply back to the newsgroup or forum for collaboration benefit among
responding engineers, and to help others benefit from your resolution.

Ace Fekay, MVP, MCT, MCITP EA, MCTS Windows 2008 & Exchange 2007, MCSE &
MCSA 2003/2000, MCSA Messaging 2003
Microsoft Certified Trainer
Microsoft MVP - Directory Services

If you feel this is an urgent issue and require immediate assistance, please
contact Microsoft PSS directly. Please check http://support.microsoft.com
for regional support phone numbers.

ACE/Meinolf

My exchange server is a stand alone server and not running on a DC, thank
God. However, my exchange server's DNS client config point to the DC1 that
froze as its Preferred Server. So in this case what would be the
consequences felt on Exchange? Outlook clients not able to communicate with
exchange because exchange cant find its Preffered DNS?


"Ace Fekay [MVP-DS, MCT]" wrote:

> "Andy3691" <> wrote in message
> news:9E95A106-23D4-4238-A49D-...
> > Hope I am posting this in the correct catagory and that you folks can help
> > clear the confusion. I have 2 DCs in my network, DC1 & DC2 with the FSMOs
> > spead out over both DCs - forest MOs on DC1 and domain MOs on DC2. These
> > are
> > also my 2 DNS servers and the are both Catalog servers. I also have a
> > DHCP
> > server on DC1 for my client workstations. All my servers are manually
> > configured with static IPs. I had DC1 freeze on me the other day and all
> > network funtionalities came to a crashing halt - outlook could not find
> > Exchange, no browsing, no VPN from outside, internet worked fine if you
> > by
> > IP address but not by resolving names . Luckly this happened after
> > business
> > hours so the mayority of users where oblivious to the outage. My
> > confusion
> > is that if I have 2 DCs also functioning as DNS with zone tranfers
> > functional
> > and up to date, why did'nt DC2 just take over automatically? My DHCP
> > server
> > has both DNS servers listed in it by IP - DC1 first then DC2. Can
> > someone
> > explain this process in laymans terms?
>
>
> Good question. This question has been asked numerous times. It's not the
> actual DNS server that "takes" over, rather it is a client-side function.
> It's based on the client-side resolver algorith. Once a client has resolved
> a query (such as to the DC, the Exchange server, or an internet address),
> the client-side resolver will keep the answer in it's local cache for the
> TTL (time to live) of the record. The TTL of a record is set on the record
> in DNS, so the client can't change that. Therefore if one DNS goes down, and
> the client already has that server cached in it's record and tries to
> communicate to it (such as Outlook, etc), it won't query the other one.
>
> Read up on it in more detail in my blog:
>
> DNS, WINS & the Client Side Resolver, NetBIOS, Browser Service, Disabling
> NetBIOS, Direct Hosted SMB (DirectSMB), If One DC is Down, Does a Client
> logon to Another DC, and DNS Forwarders Algorithm
> http://msmvps.com/blogs/acefekay/arc...algorithm.aspx
>
> If Exchange is on a DC, no need telling you that if you search on it, you
> will find numerous topics by many engineers (including Microsoft) stating
> Exchange is not recommended to be installed on a domain controller.
> Exchange's database transactional logging system is different than AD's.
> Once a machine is promoted to a DC, it disabled the write-behind cache
> function on the controller. Exchange needs this, however it's done to allow
> AD's database system properly work. A huge drawback of this scenario is that
> it can cause Exchange to lose emails during certain scenarios, as well as
> with the write-behind cache disabled, it drastically reduces performance on
> the machine.
>
> Exchange by default, will also consume all memory resources, for example,
> the store.exe process and will drag down the OS it is installed on. If the
> OS is a DC, it will hinder DC processes, such as the DC's Lsas.exe process.
> This *may* result in other issues, possibly with replication.
>
> Read more on it:
> This Exchange server is also a domain controller, which is not a recommended
> configuration
> http://technet.microsoft.com/en-us/l.../aa997407.aspx
>
> --
> Ace
>
> This posting is provided "AS-IS" with no warranties or guarantees and
> confers no rights.
>
> Please reply back to the newsgroup or forum for collaboration benefit among
> responding engineers, and to help others benefit from your resolution.
>
> Ace Fekay, MVP, MCT, MCITP EA, MCTS Windows 2008 & Exchange 2007, MCSE &
> MCSA 2003/2000, MCSA Messaging 2003
> Microsoft Certified Trainer
> Microsoft MVP - Directory Services
>
> If you feel this is an urgent issue and require immediate assistance, please
> contact Microsoft PSS directly. Please check http://support.microsoft.com
> for regional support phone numbers.
>
>
>
> .
>

"Andy3691" <> wrote in message
news:0FAFBB6C-F9C7-42EE-B3B9-...
> ACE/Meinolf
>
> My exchange server is a stand alone server and not running on a DC, thank
> God. However, my exchange server's DNS client config point to the DC1
> that
> froze as its Preferred Server. So in this case what would be the
> consequences felt on Exchange? Outlook clients not able to communicate
> with
> exchange because exchange cant find its Preffered DNS?
>

I guess you didn't read the whole blog. I mentioned this towards the end of
the blog. Sorry for the length of it. I re-arranged it and made separate
sections. Look at Section 8 called:

"What happens with Exchange and Outlook when when DNS goes down?"

And good to hear Exchange is not on a DC.

Ace

ACE,

Thanks just finished reading it, very informative my congrats.
BTW, is this the same ACE that taught at new horizons in King of Prussia Pa??

"Ace Fekay [MVP-DS, MCT]" wrote:

> "Andy3691" <> wrote in message
> news:0FAFBB6C-F9C7-42EE-B3B9-...
> > ACE/Meinolf
> >
> > My exchange server is a stand alone server and not running on a DC, thank
> > God. However, my exchange server's DNS client config point to the DC1
> > that
> > froze as its Preferred Server. So in this case what would be the
> > consequences felt on Exchange? Outlook clients not able to communicate
> > with
> > exchange because exchange cant find its Preffered DNS?
> >
>
> I guess you didn't read the whole blog. I mentioned this towards the end of
> the blog. Sorry for the length of it. I re-arranged it and made separate
> sections. Look at Section 8 called:
>
> "What happens with Exchange and Outlook when when DNS goes down?"
>
> And good to hear Exchange is not on a DC.
>
> Ace
>
>
> .
>

"Andy3691" <> wrote in message
news:6A8D080A-0549-476E-A814-...
> ACE,
>
> Thanks just finished reading it, very informative my congrats.
> BTW, is this the same ACE that taught at new horizons in King of Prussia
> Pa??
>

Yes it is. I left NH in Nov, 2005. Email me privately...


Ace