No Internet when one of my domain controller is offline

I've discovered this single point of failure on my network, and I'm
stumped.
Simply put, my network has two DC's connected to a Cisco Switch. Each
DC has only one active nic. My Router is connected to this same
switch. I found over the weekend while doing maintenance that when
DC_One was offline, none of my workstations, including the other DC,
could browse the internet. I can do dns lookups and ping external
sources just fine, but no internet browsing. When the DC in question
comes back up, everything is back to normal. Browsing returns.
How can this be? How can one machine, a machine not acting as a
router, have this effect?
I was suspicious of something in group policy, so I connected my
laptop to the switch. The laptop is not in a domain and so does not
receive policy settings. Same result; no DC_One, no internet browsing.
Any ideas greatly appreciated!

Is the DC that is offline the DNS server? Is there DNS running on the other
DC and configure on the clients as the secondary?

"Wcrouse" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I've discovered this single point of failure on my network, and I'm
> stumped.
> Simply put, my network has two DC's connected to a Cisco Switch. Each
> DC has only one active nic. My Router is connected to this same
> switch. I found over the weekend while doing maintenance that when
> DC_One was offline, none of my workstations, including the other DC,
> could browse the internet. I can do dns lookups and ping external
> sources just fine, but no internet browsing. When the DC in question
> comes back up, everything is back to normal. Browsing returns.
> How can this be? How can one machine, a machine not acting as a
> router, have this effect?
> I was suspicious of something in group policy, so I connected my
> laptop to the switch. The laptop is not in a domain and so does not
> receive policy settings. Same result; no DC_One, no internet browsing.
> Any ideas greatly appreciated!
>

Thanks for replying.

Actually, this is part of the mystery. I have three DNS Servers
running an Active Directory Integrated Zone for my domain. When one
server is down, the others continue to resolve/forward names. Also,
although my machines cannot browse the web when DC_One is offline,
they can still resolve DNS names, both internal and external,
perfectly well. DNS was my number one suspect too, but I'm darned if I
can see what's going wrong.

On Tue, 4 May 2004 07:04:05 -0400, "Rob Elder MVP-Networking"
<(E-Mail Removed)> wrote:

>Is the DC that is offline the DNS server? Is there DNS running on the other
>DC and configure on the clients as the secondary?
>
>"Wcrouse" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed).. .
>> I've discovered this single point of failure on my network, and I'm
>> stumped.
>> Simply put, my network has two DC's connected to a Cisco Switch. Each
>> DC has only one active nic. My Router is connected to this same
>> switch. I found over the weekend while doing maintenance that when
>> DC_One was offline, none of my workstations, including the other DC,
>> could browse the internet. I can do dns lookups and ping external
>> sources just fine, but no internet browsing. When the DC in question
>> comes back up, everything is back to normal. Browsing returns.
>> How can this be? How can one machine, a machine not acting as a
>> router, have this effect?
>> I was suspicious of something in group policy, so I connected my
>> laptop to the switch. The laptop is not in a domain and so does not
>> receive policy settings. Same result; no DC_One, no internet browsing.
>> Any ideas greatly appreciated!
>>
>

So what acts as your firewall? If a laptop can get all the necessary info,
IP's and etc. and do nslookups w/o this machine on then there must be
something running there that is preventing this?

--
Scott Harding
MCSE, MCSA, A+, Network+
Microsoft MVP - Windows NT Server

"Wcrouse" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Thanks for replying.
>
> Actually, this is part of the mystery. I have three DNS Servers
> running an Active Directory Integrated Zone for my domain. When one
> server is down, the others continue to resolve/forward names. Also,
> although my machines cannot browse the web when DC_One is offline,
> they can still resolve DNS names, both internal and external,
> perfectly well. DNS was my number one suspect too, but I'm darned if I
> can see what's going wrong.
>
> On Tue, 4 May 2004 07:04:05 -0400, "Rob Elder MVP-Networking"
> <(E-Mail Removed)> wrote:
>
> >Is the DC that is offline the DNS server? Is there DNS running on the
other
> >DC and configure on the clients as the secondary?
> >
> >"Wcrouse" <(E-Mail Removed)> wrote in message
> >news:(E-Mail Removed).. .
> >> I've discovered this single point of failure on my network, and I'm
> >> stumped.
> >> Simply put, my network has two DC's connected to a Cisco Switch. Each
> >> DC has only one active nic. My Router is connected to this same
> >> switch. I found over the weekend while doing maintenance that when
> >> DC_One was offline, none of my workstations, including the other DC,
> >> could browse the internet. I can do dns lookups and ping external
> >> sources just fine, but no internet browsing. When the DC in question
> >> comes back up, everything is back to normal. Browsing returns.
> >> How can this be? How can one machine, a machine not acting as a
> >> router, have this effect?
> >> I was suspicious of something in group policy, so I connected my
> >> laptop to the switch. The laptop is not in a domain and so does not
> >> receive policy settings. Same result; no DC_One, no internet browsing.
> >> Any ideas greatly appreciated!
> >>
> >
>

Might be a funny problem with the switch. Try swapping the ports the two
domain controllers are connected to and then see if you can browse with DC1
or DC2 disconnected...

--
Cheers, Mitch Tulloch
Windows Server Hacks <ISBN 0596006470>

This posting is provided AS IS with no warranties and confers no rights.

"Wcrouse" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Thanks for replying.
>
> Actually, this is part of the mystery. I have three DNS Servers
> running an Active Directory Integrated Zone for my domain. When one
> server is down, the others continue to resolve/forward names. Also,
> although my machines cannot browse the web when DC_One is offline,
> they can still resolve DNS names, both internal and external,
> perfectly well. DNS was my number one suspect too, but I'm darned if I
> can see what's going wrong.
>
> On Tue, 4 May 2004 07:04:05 -0400, "Rob Elder MVP-Networking"
> <(E-Mail Removed)> wrote:
>
> >Is the DC that is offline the DNS server? Is there DNS running on the
other
> >DC and configure on the clients as the secondary?
> >
> >"Wcrouse" <(E-Mail Removed)> wrote in message
> >news:(E-Mail Removed).. .
> >> I've discovered this single point of failure on my network, and I'm
> >> stumped.
> >> Simply put, my network has two DC's connected to a Cisco Switch. Each
> >> DC has only one active nic. My Router is connected to this same
> >> switch. I found over the weekend while doing maintenance that when
> >> DC_One was offline, none of my workstations, including the other DC,
> >> could browse the internet. I can do dns lookups and ping external
> >> sources just fine, but no internet browsing. When the DC in question
> >> comes back up, everything is back to normal. Browsing returns.
> >> How can this be? How can one machine, a machine not acting as a
> >> router, have this effect?
> >> I was suspicious of something in group policy, so I connected my
> >> laptop to the switch. The laptop is not in a domain and so does not
> >> receive policy settings. Same result; no DC_One, no internet browsing.
> >> Any ideas greatly appreciated!
> >>
> >
>

Is it posible that you have DNS forwarders configured only on the DNS server
that was down?



"Rob Elder MVP-Networking" <(E-Mail Removed)> wrote in message
news:%(E-Mail Removed)...
> Is the DC that is offline the DNS server? Is there DNS running on the
other
> DC and configure on the clients as the secondary?
>
> "Wcrouse" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > I've discovered this single point of failure on my network, and I'm
> > stumped.
> > Simply put, my network has two DC's connected to a Cisco Switch. Each
> > DC has only one active nic. My Router is connected to this same
> > switch. I found over the weekend while doing maintenance that when
> > DC_One was offline, none of my workstations, including the other DC,
> > could browse the internet. I can do dns lookups and ping external
> > sources just fine, but no internet browsing. When the DC in question
> > comes back up, everything is back to normal. Browsing returns.
> > How can this be? How can one machine, a machine not acting as a
> > router, have this effect?
> > I was suspicious of something in group policy, so I connected my
> > laptop to the switch. The laptop is not in a domain and so does not
> > receive policy settings. Same result; no DC_One, no internet browsing.
> > Any ideas greatly appreciated!
> >
>
>