Every computer on which you install Office Communications Server 2007 R2 server roles must be assigned a certificate. To assign a certificate, follow the instructions in Request a Certificate (Command Line). Note that if your configuration has multiple Front End Servers, the same certificate can be used for each of those servers. If the certificate was created with the /Exportableparameter set to True, the certificate can be exported then imported on a different computer and assigned to the server. Server roles other than the Front End Server require certificates with a subject name that matches the FQDN of the computer on which the server role is installed.