Asus RX3042H - Manual (Page 77)

RX3042H User's Manual Configuring Firewall
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• ACL Rules: for controlling all access to the computers on the
LAN and DMZ and for controlling access to external networks
for hosts on the LAN and DMZ.
• Self-Access Rules: for controlling access to the RX3042H itself.
Default Access Rules
• All traffic from external hosts to the hosts on the LAN and DMZ is
denied.
• All traffic originated from the LAN is forwarded to the external
network using NAT.
WARNING: It is not necessary to remove the default
ACL rule from the ACL rule table! It is better to create
higher priority ACL rules to override the default rule.
9.2 NAT Overview
Network Address Translation allows use of a single device, such
as the RX3042H, to act as an agent between the Internet (public
network) and a local (private) network. This means that a NAT
IP address can represent an entire group of computers to any
entity outside a network. Network Address Translation (NAT) is
a mechanism for conserving registered IP addresses in large
networks and simplifying IP addressing management tasks.
Because of the translation of IP addresses, NAT also conceals
true network address from privy eyes and provide a certain degree
security to the local network.
The NAT modes supported are static NAT, dynamic NAT, NAPT,
reverse static NAT and reverse NAPT.
9.2.1 NAPT (Network Address and Port Translation)
or PAT (Port Address Translation)
Also called IP Masquerading, this feature maps many internal hosts
to one globally valid Internet address. The mapping contains a pool
of network ports to be used for translation. Every packet is translated
with the globally valid Internet address and the port number is
translated with an un-used port from the pool of network ports.
Figure 9.1 shows that all the hosts on the local network gain access
to the Internet by mapping to only one globally valid IP address and
different port numbers from a free pool of network ports.