Usually, extending the Active Directory schema is the last step I do when installing SCCM. This time, while installing SCCM in a virtual machine, you have to provide a path to a folder with SCCM updates or download these updates from the internet. Working in a virtual machine with a “Local only” network adapter, I couldn’t download those updates; so I switch the network adapter to an external one. After downloading the updates, next step is “Installation Prerequisite Check” and at this step I extend the AD schema.

Well, the following error was written in ExtADSch.log file:
Unable to connect to RootDSE - Cannot update Active Directory. Error code = 1355.
Failed to extend the Active Directory Schema.

Error 1355 is: ERROR_NO_SUCH_DOMAIN. That means that the specified domain could not be contacted or does not exist. The problem here is that I did not switched back to “Local only” network adapter and so the Active Directory could not be contacted. Setting the adapter to “Local only”, I could contact the Domain Controller and extending the schema was successful.

What I learned? Always make sure you can reach your domain.