Active directory Login-Single Global catalog server with Two domai

[Jay]

Hi All,

I have this doubt lurking in my mind since quite some time...,

Query:
If i have two or more domains in the same forest and only one Global catalog
server in the parent/root Domain( No Global catalog servers in rest of the
doamins).
Will the users from Child domains be able to login to their respective
domains.
If yes, how does the authentication take place....?

Thanks & Regards,
Jay