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6-20 CHAPTER 6: MANUAL SETUP
PAT allows multiple private IP addresses to use one public IP address by
dynamically and statically mapping each private IP source address and private IP
source port to one public IP source address and one public IP source port.
Super NAT should be used to optimize address translation when the ISP
assigns multiple public addresses to the site.
When Super NAT is enabled, the system automatically switches between PAT
and NAT as follows:
The OCR 812 utilizes NAT until all available public IP addresses have been
used.
When all public IP addresses have been used under NAT, the system
switches to PAT in order to allow additional stations to access the Internet
(“additional” meaning “beyond those allowed by the public ports”). PAT
continues to run until a NAT port frees up.
For more information, see Super Network Address Translation (Super NAT).
set vc <vc name>
nat_option
Use the set vc <vc name> nat_option command to set the NAT operating mode
for a vc profile.
Options available for the set vc <vc name> nat_option command are
as follows:
NAT
PAT
Super_NAT
Enable
Disable
For a vc added using QuickVC, NAT is enabled by default.
Port Address Translation
(PAT)
PAT uses the TCP and UDP port numbers to map multiple private port addressed
LAN workstations (i.e. multiple users) to one public WAN port address.
Please note the following:
For normal applications such as Web browsing and FTP transfers, PAT can be
configured by just enabling the feature. When accesses are originated from the
LAN (which uses private addresses), a mapping is established between the
(LAN) source port number and the (LAN) source private address. When the
response is received on the public addressed WAN destination port, the
destination port is mapped back to the (LAN) private address.
Static PAT port mappings (or the PAT default address) must be configured
when an application will initiate a TCP or UDP connection from the public
network. If a public accessible server resides on a privately addressed LAN,
static ports can be defined for the applications they are running. For example,
TCP port 80 (for a Web server) and TCP port 21 (for an FTP server) can be
statically assigned. The PAT default address can be used with or instead of
static port assignments, and is set to the private address of a workstation on
the local LAN. If an incoming IP data packet is received on a WAN port and