Multitech RF825-E-AP User's Guide download pdf (Page 61)

Chapter 5 – Using the RouteFinder's Web Management Software

Multi-Tech Systems, Inc. RouteFinder RF825/RF825-AP User Guide (Document Number S000422B) 61

Network Setup > SNAT

The SNAT (Source Network Address Translation) process allows attaching private networks to public

networks. SNAT is used when you want to have a LAN using a private IP network to be connected to the

internet via a firewall. Since the private IP addresses are not routed on the internet, you have to apply SNAT

on the firewall’s external interface.

The RouteFinder’s internal interface serves as the default gateway for the LAN. Hence, a rule is added to the

RouteFinder to replace the source address of all packets crossing its external interface from inside to outside

with the RouteFinder’s own interface IP address. Once the request gets answered from the Internet host, the

RouteFinder will receive the reply packets and will forward them to the client on the LAN.

On this screen you can set up the RouteFinder‘s ability to rewrite the source address of in-transit data

packages using SNAT. This functionality is equivalent to DNAT, except that the source addresses of the IP

packets are converted instead of the target addresses being converted. This can be helpful in more complex

situations (e.g., diverting reply packets of connections to other networks or hosts).

Important

• For SNAT support, the TCP and/or UDP settings must be enabled in the Networks menu.

• As the translation takes place after the filtering by packet filter rules, you must allow connections that

concern your SNAT rules in Packet Filters > Packet Filter Rules with the original source address. Packet

filter rules are covered later in this chapter.

• To create simple connections from private networks to the Internet, you should use the Network Setup >

Masquerading function instead of SNAT. In contrast to Masquerading, SNAT is a static address

conversion, and the rewritten source address does not have to be one of the RouteFinder‘s IP addresses.

Add SNAT Definition – From the drop down lists, select IP packet characteristics to be translated.

Pre SNAT Source

Select the original source network of the packet. The network must be predefined in the Networks

menu. The entry is confirmed by clicking the Add button. Existing entries can be deleted or edited.

Service

Allows the corresponding service for the Pre SNAT Source entry field to be chosen from the select

menus. The service must have already been defined in the Services menu.

Destination

Select the target network of the packet. The network must have been defined in the Network menu.

The entry is confirmed by clicking the Add button. Existing entries can be deleted or edited by clicking

the Edit or the Delete buttons.

Post SNAT Source

Selects the source addresses of all the packets after the translation. Only one host can be specified

here. The entry is confirmed by clicking the Add button. Existing entries can be deleted or edited by

clicking the Edit or the Delete buttons.

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Multitech RF825-E-AP User's Guide Page 61