Nat - SMC Networks Barricade SMC7401BRA User Manual

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NAT

NAT (Network Address Translation) and NAPT (Network Address and
Port Translation) convert IP addresses on a private network (designated as
"internal" or "Local Area Network" (LAN) to global IP addresses that can
forward packets to another registered network (designated as "external" or
"Wide Area Network" (WAN), with all traffic passing through the firewall.
NAT/NAPT re-writes the IP headers of internal packets going out,
making it appear that they all came from the firewall, and enables multiple
PCs on the LAN to access the Internet for the cost of one Internet
account and one IP address. Reply packets coming back are re-translated
and forwarded to the appropriate internal machine/port. Thus, internal
machines are allowed to connect to the outside world. However, external
machines cannot find the internal machines since they are aware of only
one IP address, that of the firewall. By protecting the single network
firewall, the entire internal network can be protected.
NAPT is a special case of NAT, where many IP numbers are hidden
behind a number of addresses. In contrast to the original NAT, the number
of connections is not limited. With NAPT, an almost arbitrary number of
connections is multiplexed using TCP port information.
NAT and NAPT can also secure your network from direct attack by
hackers and provide more flexible management by allowing you to change
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