NAT Facilities
How to Set up Address Mapping
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NAT FacilitiesHow to Set up Address Mapping |
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When a PC behind NAT send an request via the router, the router will replace the IP Address with a WAN IP and by default the IP Address used for this replacement is the main WAN IP. The NAT Address Mapping function allows this to be overrided and sets the outgoing WAN IP address(es) for specific internal IP address or a block of IP addresses.
This feature can be very useful if there is a requirement for the requests to appear to come from a specific IP Address. Reasons for this might be so that the IP Address used when sending mail matches the IP Address in the MX record or if a server being contacted has an access control list or .htaccess file in place.
In this example 192.168.1.1 will be set to use 172.17.1.57 and 192.168.1.16 ~ 31 will be set to use 172.17.1.55. Any other IP Address would use 172.17.1.53.
Main WAN IP address is 172.17.1.53
To inform the router that additional IP Addresses can used for the WAN connection, the other IP addresses from IP block should be entered in the WAN IP Alias tab. Make sure Join NAT IP Pool is not checked.
By default the primay WAN IP Address (172.17.1.53 in this example) is used when replacing the private source IP Address. Therefore, unless otherwise specified, all the LAN client IP addresses will have 172.17.1.53 when send traffic to the internet.
As mentioned above, there are circumstances where you may want to use specific WAN IP from the IP block so any session a PC initiates to the internet have different WAN IP. In this example, the server with IP address 192.168.1.11 is to be presented to the internet as 172.17.1.57 and the computers with a block of IP addresses from 192.168.1.16 to 192.168.1.31 to be presented as 172.17.1.55
Please go to the NAT >> Address Mapping. The selection of subnet mask is very important when apply Address Mapping. Together subnet mask and a network address defines a specific range of IP addresses. To define a singple IP use /32. 192.168.1.16 with a subnet mask of /28 would apply to 192.168.1.16 - 31. A subnet calculator can come in handy to work out which subnet mask to use
Click index number 1 and 2 to configure the details.
The above configuration has specified the outgoing IP address(es) for a specific computer(s). For incoming traffic, you still need to open the relevant ports by using Port Redirection or DMZ functions.
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