Hi,
Prasad is right here. If only manual Authentication is requested you can handle this with one WebAS. If you need Win AD SSO on the one hand and Win AD SSO via Siteminder on the other, you need two WebAS.
Please note that you can run multiple Tomcat instances on one physical Host. But therefore you should not take the Tomcat from the BI4 Installation routine. You should download a supported Version from the Apache Foundation Homepage and install this one. You seperate the instances via different Port assignment.
Regards
-Seb.