Nat Definitions; What Nat Does; Table 26 Nat Definitions - ZyXEL Communications P-660RU-Tx User Manual

Chapter 10 Network Address Translation (NAT)

10.6.1 NAT Definitions

Inside/outside denotes where a host is located relative to the P-660RU-Tx, for
example, the computers of your subscribers are the inside hosts, while the web
servers on the Internet are the outside hosts.
Public/local denotes the IP address of a host in a packet as the packet traverses a
router, for example, the local address refers to the IP address of a host when the
packet is in the local network, while the public address refers to the IP address of
the host when the same packet is traveling in the WAN side.
Note that inside/outside refers to the location of a host, while public/local refers to
the IP address of a host used in a packet. Thus, an inside local address is the IP
address of an inside host in a packet when the packet is still in the local network,
while an inside public address is the IP address of the same inside host when the
packet is on the WAN side. The following table summarizes this information.

Table 26 NAT Definitions

ITEM
Inside
Outside
Local
Public
NAT never changes the IP address (either local or public) of an outside host.

10.6.2 What NAT Does

In the simplest form, NAT changes the source IP address in a packet received from
a subscriber (the inside local address) to another (the inside public address)
before forwarding the packet to the WAN side. When the response comes back,
NAT translates the destination address (the inside public address) back to the
inside local address before forwarding it to the original inside host. Note that the
IP address (either local or public) of an outside host is never changed.
The public IP addresses for the inside hosts can be either static or dynamically
assigned by the ISP. In addition, you can designate servers, for example, a web
server and a telnet server, on your local network and make them accessible to the
outside world. If you do not define any servers, NAT offers the additional benefit of
firewall protection. With no servers defined, your P-660RU-Tx filters out all
incoming inquiries, thus preventing intruders from probing your network.
98
DESCRIPTION
This refers to the host on the LAN.
This refers to the host on the WAN.
This refers to the packet address (source or destination) as the packet travels
on the LAN.
This refers to the packet address (source or destination) as the packet travels
on the WAN.
P-660RU-Tx User's Guide