SnapGear 2.0.1 - Manual (Page 77)

Firewall
73
Packet Filtering
By default, your CyberGuard SG appliance allows network traffic as shown in the
following table:
You can configure your CyberGuard SG appliance with additional filter rules to allow or
restrict network traffic. These rules can match traffic based on the source and destination
address, the incoming and outgoing network port, and/or the services.
You can also configure your CyberGuard SG appliance to perform network address
translation (NAT). This may be in the form of source address NAT, destination address
NAT, or 1-to-1 NAT. Network address translation modifies the IP address and/or port of
traffic traversing the CyberGuard SG appliance.
The most common use of this is for port forwarding (aka PAT/Port Address Translation)
from ports on the CyberGuard SG appliance’s WAN interface to ports on machines on
the LAN. This is the most common way for internal, masqueraded servers to offer
services to the outside world. Destination NAT rules are used for port forwarding.
Source NAT rules are useful for masquerading one or more IP addresses behind a single
other IP address. This is the type of NAT used by the CyberGuard SG appliance to
masquerade your private network behind its public IP address.
1-to-1 NAT creates both Destination NAT and Source NAT rules for full IP address
translation in both directions. This can be useful if you have a range of IP addresses that
have been added as interface aliases on the CyberGuard SG appliance’s WAN interface,
and want to associate one of these external alias IP addresses with a single internal,
masqueraded computer. This effectively allocates the internal computer its own real
world IP address, also known as a virtual DMZ.
Function NAT Method
Port forwarding (PAT) Destination NAT
Masquerading Source NAT
Virtual DMZ 1-to-1 NAT
Incoming Interface Outgoing Interface Action
LAN/VPN/Dial-In Any Accept
DMZ WAN Accept
DMZ Any except WAN Drop
WAN Any Drop