Hi
I'm having problems with name resolution.
Scenario:

1 - Site1 -> Tree Root Domain (domain.root) -> 4 Domain Controllers all with
Dns Service Installed, AD integrated, replication only between DNS servers
on the tree root domain. (This DNS has 1 delegation for the child domain)
Site1 - Subnet 192.168.0.x/24.
   1- DC - 192.168.0.254
   2- DC - 192.168.0.253
   3- DC - 192.168.0.252
   4- DC - 192.168.0.251

2 - Site2 -> Child Domain of the tree root (child.domain.root) -> 1 Domain
Controller with DNS server installed, AD integrated, replication only
between DNS servers on the child domain. (This DNS has 1 delegation for the
grandchild domain) Site2 - Subnet 192.168.1.x/24.

3 - Site3 -> GrandChild Domain of the child.domain.root -> 1 Domain
Controller with DNS server installed, AD integrated, replication only
between DNS servers on the Grandchild domain.Site2 - Subnet 192.168.2.x/24.

The sites are all connected trough routers.

The problem:
The problem refers only to the Tree root resolution.

When we try to ping the domain.root from the child or the grandchild
domains, if all Dns Servers are online there is no problem.

But If we have for example the DC 2 (192.168.0.253) and the DC 3
(192.168.0.252) and the DC 4 (192.168.0.251) Offline, then sometimes we
can't resolve the domain.root.

I run nslookup from the childs domain and i'm able to see all NS records
refering to DC1,DC2,DC3 and DC4.
It seams that when the DCs are offline (disconnected or not accessible), the
DNS on child and grandchild domains aren't able to verify which dns are
offline and returns the address of the disconnected DCs. For example with DC
2,3,4 disconnected and the DC1 connected if I try to ping domain.root it
returns the address of the DC2 which is 192.168.0.253 or sometimes returns
the address of the DC3 which is 192.168.0.252 and so on, and off course with
this behavior the request times out.
Only sometimes it returns the right address of the DC that is connected.

Is this normal??? Is this have to do with the fact that the sites are
connected trough routers and the dns aren't able to see which dns are
offline???
What is the best way to resolve this??

Regards.