Question : CHILD DOMAIN DNS

Hi all,
We have 5 child domains with different sites(fully ip routed)
Site Design :-
Root DC - NSROOT.net
Child dc- Apac.nsroot.net,nam.nsroot.net,Jpn.nsroot.net,aus.nsroot.net and eur.nsroot.net.
My replication topology is Hub and spoke.
where Newyork(Nsroot.net) site is hub and rest of the site are  spokes.
Each and every site is having a global catalog serves.
I am confused about DNS.
All the dns in each child domain are active directory intergrated zone.
Each child dns is pointing to their own dns server for all the clients.
In my root domain(nsroot.net) replication scope is set to "Repliacte to all DNS servers in the forest"
I am able to see nsroot.net zone in all child domains.
Question : 1
It is right to set the replication scope to  "Replicate to all DNS servers in the forest" in root domain.Any bandwidth issue will appear.
Qusetion:2
What is forest DNS zone and Domain DNS zone.
Question -3
How does child domain clients will identify the GC server via dns.I am able to see GC srv record in rootdns zone.
Appreciate for your help ....
Thanks all

Answer : CHILD DOMAIN DNS

I will answer question 2 first.
ForestDNSZones is an Application partition that is replicated to all DNS servers in the forest that are DCs.  Therefore, any zone stored in here will be available on every DNS server in the forest as long as it is a DC.
DomanDNSZones in an Applicacation partition that is replicated only to DNS servers in its domain that are DCs. Therefore, any zone stored in here will only be available on DNS server in that domain as long as it is a DC.

Answer to question 1.
If a zones replication scope is "Replicate to all DNS servers in a forest" you are storeing that zone in the ForestDNSZones application partition.  Once the zone has replicated around you network unless you have a huge network (or a very slow one) there should not be too many bandwidth issues.

Answer to question 3.
GCs register their records in the _msdcs.nsroot.net zone, which should be a zone created during DCPromo (if you installed DNS during DCPromo and you are using Windows 2003 or later) and is stored in the ForestDNSZones Application partition.

If you don't have all zones present on each DNS server you should verify that you can resolve names accross all domains.