There are three ways to modify the schema: through the Schema Manager MMC, using LDIF files, or programmatically using ADSI. We will not cover the use of the Schema Manager MMC very heavily here since it is fairly straightforward to use, although we will cover its use in managing the Schema FSMO role. Typically you should not use the Schema Manager MMC to extend the schema and instead use LDIF files or ADSI. Most vendors provide LDIF files, which contain the schema extensions that you can run at your leisure. We cover extending the schema with ADSI in Chapter 24.
The Schema Manager MMC is not available from the Administrative Tools menu like the other Active Directory snap-ins. To use it, you need to first register the Dynamic Link Library (DLL) file for the MMC snap-in by typing the following command at the command prompt:
You can then start the Schema Manager console by creating a custom
MMC and adding the Active Directory Schema snap-in to it. To create a
console, go to the Run menu from the Start button, type
mmc.exe, and click OK. Then in the empty MMC,
choose the Console menu and select Add/Remove Snap-in. From here, you
can click the Add button and select Active Directory Schema as the
item. If you then click the Add button, followed by Close, and then
the OK button, that will give you an MMC hosting the Schema Manager
snap-in for you to use and later save as required.