Chat install on mutil servers

I have the paid version of Zimbra 8.09 I watn to user the Zxtras chat modules.
In testing I have installed on two servers with a single ldap
The users on server 1 can chat with each other the user on server 2 can chat with each other but I cannot get the a user on server 1 to chat with a user on server 2
Is this function supported? or did I miss an install step?