OWA failover

Hello,

 

We have two sites, production and DR; each site has an identical setup which consists of LTM, GTM, Juniper SA, and MS Exchange 2007 infrastructure in addition to some other web applications.

 

The main requirement is to automatically fail users over to the DR site in case of any partial failure within production.

 

Remote users connect to their email through the Juniper SSL VPN where they use OWA from there.

 

Now I want to make sure that in case the Exchange system in production is down, VPN user to automatically connect to the Exchange CAS node located at the DR site (which includes the IIS for OWA) even if the Exchange setup is not running there.. A WAN link between the two sites is already there

 

 

Can any one help me how to acheive this?

 

 

Thx,