Question : Active Directory Design with Child domain authenticating to Parent Domain

We are designing Active Directory and had some questions pertaining to authentication and child domains.

Here is the synopsis:

One parent domain, in its own subnet, with one DC
Four child domains, in their own subnets, with their own respective DC.
One DHCP server residing in the parent domain with scopes defined for all 5 subnets and an "IP Helper Address", with the DHCP server's IP address, defined on the Routers Child domain interface.
All five subnets are seperated by routers with Fast Ethernet interfaces (e.g. fa0/0 & fa0/1).

If a "Child Domain's DC" goes offline in any of the child subnets:
1. Can servers & workstations, in the child domain, authenticate with the parent domains DC without any manual intervention by IT Staff?
2. What ports need to be enabled on the routers fa0/0 & fa0/1 interfaces if Number 1 is true?
3. What other issues such as DNS & DHCP might be at risk in this scenario if Number 1 is true?

Thank you,

Tom

Answer : Active Directory Design with Child domain authenticating to Parent Domain

not exactly, i was thinking more along the lines of a single group for eash site...say all members of site a belong to group siteA   ..in site A you configure you permissions using the SiteA group and thats it...Site B has a similar config and so do sites C and D