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In many voice networks, the voice devices have private addresses (indicated by 10.x.x.x), while the WAN link may have a public address (indicated by b.x.x.x). You can assign private addresses to both Cisco CME (if present in the deployment) and Cisco Unity Express in order to fit in a large network and also for voice security reasons.

If you choose this design, then remote management access via HTTP—for the Cisco Unity Express or Cisco CME graphical user interface (GUI)—must pass through Network Address Translation (NAT) to be able to reach the Cisco Unity Express module. The GUI uses both the Cisco IOS HTTP server as well as an HTTP server on the Cisco Unity Express module.