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PPENDIX
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DDRESS
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RANSLATION
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UTORIAL
Static NAT Static NAT operates like Dynamic NAT except you may add entries to the
address translation table and indicate specific IP addresses from the pool
to map to specific private LAN IP addresses. This allows controlled access
by the outside world.
Port Address
Translation (PAT)
PAT is used when several privately addressed workstations share a single
public address. PAT uses the TCP and UDP port numbers to map multiple
private addresses to the single public address. 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 private
addressed LAN, a mapping is established between the source port
number and the source private address. When the response is received on
the public addressed WAN port, the destination port is mapped back to
the private address.
Static PAT port mappings or the PAT default address need to be
configured when an application will initiate a TCP or UDP connection
from the public network. If a publicly 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 a 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 there is no
existing dynamic or static port mapping, the packet will be translated
using the PAT default address.
PAT Example Your remote site administrator or ISP provides one address for the
OfficeConnect Remote 840's Local WAN IP address (In the example
above, 10.0.0.1). You make up a private IP network for the LAN and
assign an IP address from that network to each workstation and to the
OfficeConnect Remote 840 (LAN IP address).
RIP (if enabled) must be set to “listen only” so the OfficeConnect Remote
840 will learn routing information from the WAN but will not broadcast
the private network information.
840ug.book Page 4 Friday, July 7, 2000 2:23 PM