Netgear UTM9S – ProSECURE Unified Threat Management (UTM) Appliance with DSL and Wireless modules 参照マニュアル

interfaces on the UTM9S (one DSL and two WAN interfaces), the one remaining interface 
is disabled. As long as the primary link is up, all traffic is sent over the primary link. When 
the primary link goes down, the rollover link is brought up to send the traffic. When the 
primary link comes back up, traffic automatically rolls back to the original primary link.

If you want to use a redundant ISP link for backup purposes, select the DSL or WAN 
interface that needs to function as the primary link for this mode. Ensure that the backup 
interface has also been configured and that you configure the WAN failure detection 
method on the WAN Advanced Options screen to support auto-rollover (see 

Whichever WAN mode you select, you also need to select either NAT or classical routing, as 
explained in the following sections.

Configure Network Address Translation

Network Address Translation (NAT) allows all PCs on your LAN to share a single public 
Internet IP address. From the Internet, there is only a single device (the UTM9S) and a single 
IP address. PCs on your LAN can use any private IP address range, and these IP addresses 
are not visible from the Internet.

Note the following about NAT:

The UTM9S uses NAT to select the correct PC (on your LAN) to receive any incoming 

data. 

If you have only a single public Internet IP address, you need to use NAT (the default 

setting).

If your ISP has provided you with multiple public IP addresses, you can use one address 

as the primary shared address for Internet access by your PCs, and you can map 
incoming traffic on the other public IP addresses to specific PCs on your LAN. This 
one-to-one inbound mapping is configured using an inbound firewall rule.