Telindus 1031, User And Reference Manual

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Telindus 1031 Router Chapter 7
User manual Configuring the router
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7.4.8 How does the NAT address table work?
If a local station sends data to the Internet for the first time, NAT looks for an unused official IP address.
It assigns this official IP address to the local station. The amount of local stations that can have simulta-
neous Internet access equals the amount of NAT addresses you defined. If all sessions between a local
station and the Internet have been closed by the application (in case of TCP) or because of time-outs,
then the previously assigned official IP address is freed for another local station.
Optionally, the NAT address entry may contain a corresponding private IP address. This allows to per-
manently assign an official IP address to a local station. This is useful for stations or servers that should
have Internet access at all times. Another example of permanently assigned official IP addresses is a
network where only a limited number of users has Internet access.
NAT only converts IP addresses and thus allows traffic in both directions. However, incoming traffic on
one of the official IP addresses can only be forwarded to the local network if a corresponding private IP
address has been configured.
Example of a NAT address table
In this example, the first address is continuously assigned
to a server with IP address 192.168.47.250. The others are
assigned dynamically.