Multitech MultiAccess MULTIACCESS MA30120, Руководство пользователя

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Chapter 3 – Software
MultiAccess Communications Server MA30120 User Guide 63
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 private IP network connected to the Internet via the MultiAccess, since
the private IP addresses are not routed on the Internet, you have to apply SNAT on the MultiAccess’s public
interface.
The MultiAccess’s internal interface serves as the default gateway for the LAN. Hence, a rule is added to the
firewall to replace the source address of all packets crossing the MultiAccess’s external interface from inside to
outside with the MultiAccess’s own IP address. Once the request gets answered from the Internet host, the
firewall will receive the reply packets and will forward them to the client on the LAN.
On this screen you can set up the MultiAccess‘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 at
Networks & Services >
Services > Protocol
.
Important:
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.
Note:
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 MultiAccess‘s IP addresses.
Add SNAT Definition
From the drop down list boxes, select IP packet characteristics to be translated. The options are:
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 by clicking
the
Edit
or the
Delete
buttons.
Service
Allows the corresponding service for the Pre SNAT Source entry field to be chose 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
Networks
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.