Polycom 4300T - Manual (Page 50)

User Guide V 2 IU 4300T Converged Network Appliance
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Data Networking Configuration
The 4300T provides static IP routing and two types of Network Address
Translation (NAT) functions for data traffic. This section describes the use and
configuration of these features.
NAT for Data Traffic
NAT allows hosts on a private internal network (the LAN side of the 4300T) to
anonymously communicate with devices on an external network (the WAN
side of the 4300T). The 4300T with NAT enabled will re-write outbound
packet headers using public IP addresses in place of private IP addresses so
that the private IP addresses are not exposed to the external network.
Additionally, the ports used by the IP addresses are also changed as they
traverse the 4300T. This is known as Port Address Translation (PAT) and
provides an additional security measure. The 4300T maintains a table of these
mappings so that return packets can be forwarded to the correct host on the
private network.
The 4300T provides two types of NAT functions: dynamic NAT and static
NAT. Dynamic NAT allows many private IP addresses to be mapped to a
single public IP address (using different port numbers of the public IP
address). Static NAT maps private IP addresses and port. For example,
mapping a public IP address to a specific machine on the private network
responsible for receiving email.
Note The 4300T ALG automatically handles NAT for voice devices.