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Page 116 / 268 Scroll up to view Page 111 - 115
Chapter 9 DHCP Server
NBG4604 User’s Guide
116
Page 117 / 268
NBG4604 User’s Guide
117
C
HAPTER
10
Network Address Translation
(NAT)
10.1
Overview
This chapter discusses how to configure NAT on the NBG4604.
NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP
address of a host in a packet. For example, the source address of an outgoing
packet, used within one network is changed to a different IP address known within
another network.
Each packet has two addresses – a source address and a destination address. For
outgoing packets, NAT maps private (local) IP addresses to globally unique ones
required for communication with hosts on other networks. It replaces the original
IP source address in each packet and then forwards it to the Internet. The
NBG4604 keeps track of the original addresses and port numbers so incoming
reply packets can have their original values restored. The following figure
illustrates this.
Figure 71
NAT Example
For more information on IP address translation, refer to
RFC 1631
,
The IP Network
Address Translator (NAT)
.
Page 118 / 268
Chapter 10 Network Address Translation (NAT)
NBG4604 User’s Guide
118
Note: You must create a firewall rule in addition to setting up NAT, to allow traffic from
the WAN to be forwarded through the NBG4604.
10.2
What You Can Do
•
Use the
General
screen (
Section 10.3 on page 118
) to enable NAT and set a
default server.
•
Use the
Application
screen (
Section 10.4 on page 119
) to change your
NBG4604’s port forwarding settings.
•
Use the
Advanced
screen (
Section 10.5 on page 122
) to change your
NBG4604’s trigger port settings.
10.3
General NAT Screen
Use this screen to enable NAT and set a default server. Click
Network > NAT
to
open the
General
screen.
Figure 72
Network > NAT > General
The following table describes the labels in this screen.
Table 47
Network > NAT > General
LABEL
DESCRIPTION
NAT Setup
Enable Network
Address
Translation
Network Address Translation (NAT) allows the translation of an Internet
protocol address used within one network (for example a private IP
address used in a local network) to a different IP address known within
another network (for example a public IP address used on the Internet).
Select the check box to enable NAT.
Default Server Setup
Page 119 / 268
Chapter 10 Network Address Translation (NAT)
NBG4604 User’s Guide
119
10.4
NAT Application Screen
Use the
Application
screen to forward incoming service requests to the server(s)
on your local network. You may enter a single port number or a range of port
numbers to be forwarded, and the local IP address of the desired server. The port
number identifies a service; for example, web service is on port 80 and FTP on
port 21. In some cases, such as for unknown services or where one server can
support more than one service (for example both FTP and web service), it might
be better to specify a range of port numbers.
In addition to the servers for specified services, NAT supports a default server. A
service request that does not have a server explicitly designated for it is forwarded
to the default server. If the default is not defined, the service request is simply
discarded.
Note: Many residential broadband ISP accounts do not allow you to run any server
processes (such as a Web or FTP server) from your location. Your ISP may
periodically check for servers and may suspend your account if it discovers any
active services at your location. If you are unsure, refer to your ISP.
Port forwarding allows you to define the local servers to which the incoming
services will be forwarded. To change your NBG4604’s port forwarding settings,
click
Network > NAT
>
Application
. The screen appears as shown.
Note: If you do not assign a
Default Server
IP address
in the
NAT >
General
screen,
the NBG4604 discards all packets received for ports that are not specified in
this screen or remote management.
Server IP
Address
In addition to the servers for specified services, NAT supports a default
server. A default server receives packets from ports that are not
specified in the
Application
screen.
If you do not assign a
Default
Server
IP address
, the NBG4604
discards all packets received for ports that are not specified in the
Application
screen or remote management.
Apply
Click
Apply
to save your changes back to the NBG4604.
Reset
Click
Reset
to begin configuring this screen afresh.
Table 47
Network > NAT > General
LABEL
DESCRIPTION
Page 120 / 268
Chapter 10 Network Address Translation (NAT)
NBG4604 User’s Guide
120
Refer to
Appendix E on page 251
for port numbers commonly used for particular
services.
Figure 73
Network > NAT > Application
The following table describes the labels in this screen.
Table 48
Network > NAT > Application
LABEL
DESCRIPTION
Add Application Rule
Active
Select the check box to enable this rule and the requested service can
be forwarded to the host with a specified internal IP address.
Clear the checkbox to disallow forwarding of these ports to an inside
server without having to delete the entry.
Service Name
Type a name (of up to 31 printable characters) to identify this rule in
the first field next to
Service Name
. Otherwise, select a predefined
service in the second field next to
Service Name
. The predefined
service name and port number(s) will display in the
Service Name
and
Port
fields.
Local Port
Range
Public Port
Range
Enter the port number ranges to be forwarded.
Server IP
Address
Type the inside IP address of the server that receives packets from the
port(s) specified in the
Port
field.
Apply
Click
Apply
to save your changes to the
Application Rules Summary
table.
Reset
Click
Reset
to not save and return your new changes in the
Service
Name
and
Port
fields to the previous one.

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