Using Variables as Entry in a Remote Desktop Hostname Destination

A couple things...

If you log the RDTOP variable (log local0. "RDTOP: $RDTOP), does it show you that value that you expect in the ltm log?

Also, I think a problem is that you're setting a variable in an iRule, but that variable is not going to be accessible from the RDP profile. What you should do is use ACCESS::session to set a session variable and use that. So you'd add something like this to the iRule: ACCESS::session data set session.custom.rdpname $RDTOP. Then in your RDP resource, you could set the host to %{session.ustom.rdpname}.

Hope this helps.