We wererunning two Exchange 2007 CAS load balanced by F5(BigIP Load balancer) plus two HUB and a CCR Cluster in same AD site called Site1. Because of organization movement to new location we moved one CAS server to new location which have totally new AD site called Site2. Both sites have full internet connectivity. Also the F5 load balancer is moved to Site2 form Site1. Now the problem if we keep running with one CAS server which is in Site1 with all active mailbox servers, everything works ok. But the moment we include newly moved CAS (Site2) in F5 Server pool, users start getting error messages in OWA like "For best performance you should be using this url: https://site1.contoso.com" Even viewer on Site2 CAS is showing following error messages: "CAS server CAS01 failed to proxy EWS to AD site CN=Site1 because none of the CAS servers in this site are responding. Please check the configuration and status of the servers in site CN=Site1" What can be the issue, I want to both CAS servers should be working through F5 load balancer even though both are residing in different AD sites? Note: All subnets are properly mapped to relevant AD sites.