Should you or shouldn't you have two Global Catalogs on a small network? Microsoft isn't very clear on this.

Posted on 2005-05-10
Last Modified: 2010-04-14
We have a small network(windows 2000 server(2), exchange server 2000, and about 50 PCs. Server 1 has the exchange server and is the original server. It is also in charge of DNS & DHCP for our network. Server 2 came along as a result of needing to have a host for Backup Exec for windows servers and that's pretty much all that's expected of it. So, I wanted it to act as a backup top Server 1 in case of server 1's being down for maintenence or whatever. I have tried setting up replication between the two and am not convinced that I have succeeded with that. But as I'm reading the Help documents from Microsoft that pertain to the Active directory connector, I come across a prompt that says that the server I have selected for the connection (#2) is not a global catalog. and it "strongly" reccomends that the connection be made to a global catalog. So I begin a bit of searching in the help files regarding "global catalogs". I come across some info under the heading, "disabling" global catalog. It says that the global catalog is initiated by default and the "enable/disable" option can be found in the sites and services msc, under sites/server/ntds/properties. I looked and found that server 1 is enabled while server 2 is not. The help file states,


Do not enable this option unless you are certain it will provide value in your deployment. For this option to be useful, your deployment must have multiple domains, and even then, only one global catalog is typically useful in each site."

OK, we only have one domain so it makes me wonder if we don't need it. Reading further on in the same article it goes on to say,

"Clients must have access to a global catalog to log on, so you should have at least one global catalog in every site to receive the benefits of containing network traffic provided by using sites."

Now that sounds as if it's absolutely necessary if anyone ever hopes to log on. So far if server 1 goes down, no one can log on, I'm getting replication errors that make me question whether the replication is working (not to mention the inability to log on when server 1 goes down). So my question is: given the size of our site and the fact that we have only 1 domain & 2 servers, should I have both set to be global catalogs?
Question by:dwielgosz
    LVL 18

    Expert Comment

    It is necessary to have a GC in order for your users to log onto the domain. So if server 1 goes down and server 2 is not a GC then even though it is a DC, your users won't be able to log on. So yes, it is a good idea to make both of your domain controllers GCs as well.

    Also see this article:

    Author Comment

    So, if both are GCs, then if #1 goes down #2 will handle logons? As simple as that?
    LVL 18

    Accepted Solution

    Pretty much atleast for a temporary time while you get your first DC back up. You should also run DNS on the second DC as well.

    Author Comment

    So as far as the #2 server and DNS is concerned, do I set DNS up to be identical to server #1 then?

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