Exchange 2010 OWA Multisite

Hello to all the community 

I have a little problem with my OWA On my site number 2. 

I have my HUB1, CAS1, MB1 connected via a DAG side on my MB2 

And I have my site HUB2, CAS2, MB2 in case of problems on the first .... 

On my CAS2, OWA does not work even when I configure such that the CAS1 .... a solution? 

Thank you very much for your help, 

Regards,