Chapter 5 – Using the RouteFinder's Web Management Software
Multi-Tech Systems, Inc. RouteFinder RF825/RF825-AP User Guide (Document Number S000422B)
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Network Setup > SNAT
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.
