Thats a tough question without know much more information about your environment. In general it is desirable to design a single domain model. Windows 2000 is truely a scable network operating system. Unlike Windows NT 4.0, you do not have to worry about how many users/groups/resources are going to be in your company. Windows 2000 can handle all of them in one domain (NT 4.0 has a limit..2000 has a limit but its so big that most companies will not approach it.).
MS recommends one domain if possible. If you have a company structure that is stricly managed by departments, you may want to consider more domains.
You will not run into ROUTER performance problems with Windows 2000. This is because of a concept called SITES. Here is a quick example:
Say you have one single domain. This domain spans 3 physical locations (London, New York, and China).
In Active directory, you specify your network envirnment subnets that pertain to each location. So..it would look something like this: London site = 10.1.10.x, New York site= 192.1.10.x, and China site= 165.1.10.x.
Then you tell Active Directory where you domain controller are located. Lets say 3 DC's in each site (3 in London, 3 DC's in NY, and 3 DC's in China)
Because these site boundaries are defined, DC's will replicate very fequently with other DC's located in the same site (the Knowledge Consistency Checker helps with this). Then, at a slower rate and compressed, DC's between sites will replicate. You can specify how often and at what times replication should occur. In this way, you are "saving" your WAN link bandwidth for other data transmits.
In addition, because sites are defined, all users will logon to a DC within thier same site. This resolves the problem in NT 4.0 where you may log on across a WAN link even though a DC was availble on your local LAN.
Hope some of this helps...
Later
Joseph L. Poandl
MCSE 2000
