Domino Server 9.0.1 DAS option is not available in Additional Server mode

Question

I installed Domino Server 9.0.1 and lotus Notes. The Enable DAS option is not available at all in the web Engine tab at all.

How can II enable it as 9.0.1 must support it by default! I am using the Enterprise version. Do I need to install some plugin?

UPDATE

I tried to uninstall it and install it again ,this time selecting standalone mode and the option is available if "Load Internet configurations from Server\Internet Sites documents" to disabled as @Knut Herrmann mentioned.

The issue is that I have to use this domino server as additional server and in that mode I am not getting this option

UPDATE 2

I am using Domino server 9.0.1 in additional server mode, that connects to a main server for syncing the data which has a Domino server 8.5.3 . I am not able to get the option under Web Engine tab to enable DAS.

Answer 1

Set field "Load Internet configurations from Server\Internet Sites documents" to disabled on server document's basic tab:

Only if this option is disabled the section "Domino Access Services" on tab "Internet Protocols / Domino Web Engine" is visible.