Is the GC server supposed to be enabled by default in child doamin?

Thanx! What do you mean " make sure your GC role doesnt sit on the infrastructure master? " 

you cannot have the infrastructure master role on the same server as a Global Catalog server - a GC holds a partial replica of every object in the domain, if you place the GC role on the inf master, nothing will get updated :)
http://support.microsoft.com/kb/223346

But this sounds weired... When you install the first DC in the forest, it has the GC enabled by default and it also has the 5 single master roles by default. So if I only have 1 DC, what can I do?

the rule only comes into play when you introduce a child domain - in a single domain environment it doesnt matter

you should have two DC's my friend, if you are going to use child domains, then in particular your root domain should have redundancy

Let me clarify. In a single domain it does not matter which machines are Infrastructure Masters and which are Global Catalog servers, neither does it matter in a multi-domain environment where ALL Domain controllers are also Global Catalogs.

The advice about not having Global Catalog and the Infrastructre master on the same machine ONLY applies in a multiple domain where only some of the DCs are global catalogs. In such a situaltion false "phantoms" can occur.

much better way of putting it

Thank you for the explanation. So if I have a single doamin,  with 2 DCs. It doesn't matter if the GC also have the 5 single master roles.

If I have a child domain and it only has 1 DC, it also doesn't matter.
But if I have 2 DCs in child domain, I should only enable GC on second DC.

Is my above statement correct? Thank you.

if you have a child domain with 2DC's and a root domain with only 1 DC then your priorities are a little bit out of line - it should be the reverse

but yes, you are getting the right idea

Thanx Jay_Jay70!! But I don't understand what you mean "priorities are a little bit out of line - it should be the reverse" ?? what properties?? and which one should be reverse?

you have a root domain - that should have 2DC's not the child...You should ideally of course have two DC's per Domain, but when dealing with child domains, you should ALWAYS have 2 DC's in the root

you mean I must have 2 DCs in root domain if I want to create a child domain? why? I have only 1 DC in root domain and 1 DC in child domain, but I didn't see any problem.....

its not a "must" it wont give you any problems functionality wise, but you have no redundancy, and if you lose your root domain, you are screwed big time...you have to rebuild both domains..

Ok. Thank you! Because you said "you should ALWAYS ...." So I thought you mean must...

lol, pleasure - but keep in mind you run a big risk if you run just a single DC in the root :)

Sorry.. just a last question... if you say redundancy is important for root domain, so how about child domain? redundancy is not that important in child domain?

nowhere near as important - i mean, sure, you should still have multiple DC's or you will lose the child, but at worst, you lose the child, not the entire structure

Thank you so much!

pleasure

Hi Jay_Jay70, May I ask you another question on the GC again here?  https://www.experts-exchange.com/questions/23477107/Without-GC-why-I-can-still-to-joing-the-domain.html

Do you know how should I configure this? https://www.experts-exchange.com/questions/23483921/what-is-the-Site-and-service-configuration-for-child-doamin-in-different-site.html