Polycom MGC Administrator Administrator's Manual page 138

Chapter 3 - Defining Network Services
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between them. If these ports are not defined in the system, ports are
randomly allocated, which can result in the firewall allocating a
wider range of ports and thus be vulnerable to unauthorized network
access.
NAT (Network Address Translation) Traversal is a mechanism used
translate the internal IP address into a public IP address. In this
dialog box you define the external IP address that will be used for
the translation of the internal addresses. For more information, see
"NAT Traversal" on page E-5.