Win 2012 RDS farm not accessible over DA

Hi,

I have build an RDS farm using 3 win 2012 ( 1 broker and 2 session host, no gateway)

I do have  multisite 2012 DA environment

End users are able to open web url page of RDS, but cannot further remote into any terminal server or open remote app.

same works fine within LAN or using older SSTP based VPN. 

I am able to remote into all 3 RDS servers separately over DA, but not via farm.

BR