Network Address Translation (NAT)
NAT allows the addresses used within your LAN to be replaced by a different address when connecting to an external service.
Typically a service provider will allocate you a single IP address to be used when connecting to their service. NAT allows all your user's traffic to appears to be coming from that single address without having to change any of your user's real addresses. This is useful as internally most networks use addresses that have been reserved for public use within networks but are not valid for routing across the internet (since the same addresses may be being used on other networks). Also as stated it allows multiple users to use the same service simultaneously.
The use of NAT is automatically enabled if the IP Office Service being used includes an IP address that is not in the same domain as the its LAN1 IP address.
An exception to the above applies for the Small Office Edition and IP412 control units. These units have two LAN's, LAN1 and LAN2. For these units, on each LAN, Enable NAT can be selected and then applied to traffic between the two LAN's.
Dynamic Host Configuration Protocol (DHCP)
The IP Office can act as a simple DHCP server. When switched on with a defaulted configuration, the Control Unit request IP address information from a DHCP server. If it gets no response it assumes the role of DHCP server for the LAN.
In DHCP Server mode, by default the Control Unit issues itself the address 192.168.42.1. It allocates 200 addresses for DHCP clients, 192.168.42.1 to 126.96.36.199. This leaves 192.168.42.201 to 192.168.42.254 available for any computers that need to be allocated a fixed or static IP address. 192.168.42.255 is not used as this is a broadcast address for the LAN.