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Page 106 / 244 Scroll up to view Page 101 - 105
Chapter 11 Network Address Translation (NAT)
NBG-416N User’s Guide
106
Refer to
Appendix E on page 205
for port numbers commonly used for particular
services.
Figure 62
Network > NAT > Application
The following table describes the labels in this screen.
Table 42
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
Type a port number(s) to be forwarded.
To specify a range of ports, enter a hyphen (-) between the first port
and the last port, such as 10-20.
To specify two or more non-consecutive port numbers, separate them
by a comma without spaces, such as 123,567.
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.
Page 107 / 244
Chapter 11 Network Address Translation (NAT)
NBG-416N User’s Guide
107
11.5
Technical Reference
The following section contains additional technical information about the NBG-
416N features described in this chapter.
11.5.1
NAT Port Forwarding: Services and Port Numbers
A port forwarding set is a list of inside (behind NAT on the LAN) servers, for
example, web or FTP, that you can make accessible to the outside world even
though NAT makes your whole inside network appear as a single machine to the
outside world.
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
Reset
Click
Reset
to not save and return your new changes in the
Service
Name
and
Port
fields to the previous one.
Application Rules Summary
#
This is the number of an individual port forwarding server entry.
Active
This icon is turned on when the rule is enabled.
Name
This field displays a name to identify this rule.
Local Start/End
Port
Public Start/End
Port
This field displays the port number(s).
Protocol
This field displays the traffic protocol type.
Server IP
Address
This field displays the inside IP address of the server.
Modify
Click the
Edit
icon to display and modify an existing rule setting in the
fields under
Add Application Rule
.
Click the
Remove
icon to delete a rule.
Table 42
Network > NAT > Application (continued)
LABEL
DESCRIPTION
Page 108 / 244
Chapter 11 Network Address Translation (NAT)
NBG-416N User’s Guide
108
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.
11.5.2
NAT Port Forwarding Example
Let's say you want to assign ports 21-25 to one FTP, Telnet and SMTP server (
A
in
the example), port 80 to another (
B
in the example) and assign a default server IP
address of 192.168.1.35 to a third (
C
in the example). You assign the LAN IP
addresses and the ISP assigns the WAN IP address. The NAT network appears as a
single host on the Internet.
Figure 63
Multiple Servers Behind NAT Example
Page 109 / 244
NBG-416N User’s Guide
109
C
HAPTER
12
Firewall
12.1
Overview
Use these screens to enable and configure the firewall that protects your NBG-
416N and your LAN from unwanted or malicious traffic.
Enable the firewall to protect your LAN computers from attacks by hackers on the
Internet and control access between the LAN and WAN. By default the firewall:
•
allows traffic that originates from your LAN computers to go to all of the
networks.
•
blocks traffic that originates on the other networks from going to the LAN.
The following figure illustrates the default firewall action. User
A
can initiate an IM
(Instant Messaging) session from the LAN to the WAN (
1
). Return traffic for this
session is also allowed (
2
). However other traffic initiated from the WAN is blocked
(
3
and
4
).
Figure 64
Default Firewall Action
12.2
What You Can Do
•
Use the
General
screen
to enable or disable the NBG-416N’s firewall (
Section
12.4 on page 111
).
Page 110 / 244
Chapter 12 Firewall
NBG-416N User’s Guide
110
•
Use the
Services
screen to enable or disable ICMP and VPN passthrough
features (
Section 12.5 on page 111
).
12.3
What You Need To Know
The NBG-416N’s firewall feature physically separates the LAN and the WAN and
acts as a secure gateway for all data passing between the networks.
12.3.1
About the NBG-416N Firewall
The NBG-416N firewall is a stateful inspection firewall and is designed to protect
against Denial of Service attacks when activated (click
the
General
tab under
Firewall
and then click the
Enable
Firewall
check box). The NBG-416N's
purpose is to allow a private Local Area Network (LAN) to be securely connected to
the Internet. The NBG-416N can be used to prevent theft, destruction and
modification of data, as well as log events, which may be important to the security
of your network.
The NBG-416N is installed between the LAN and a broadband modem connecting
to the Internet. This allows it to act as a secure gateway for all data passing
between the Internet and the LAN.
The NBG-416N has one Ethernet WAN port and four Ethernet LAN ports, which are
used to physically separate the network into two areas.The WAN (Wide Area
Network) port attaches to the broadband (cable or DSL) modem to the Internet.
The LAN (Local Area Network) port attaches to a network of computers, which
needs security from the outside world. These computers will have access to
Internet services such as e-mail, FTP and the World Wide Web. However, "inbound
access" is not allowed (by default) unless the remote host is authorized to use a
specific service.
12.3.2
VPN Pass Through Features
A Virtual Private Network (VPN) is a way to securely connect two networks over
the Internet. For example a home network and one in a business office. This
requires special equipment on both ends of the connection.
The NBG-416N is not one of the endpoints but it does allow traffic from those
endpoints to pass through. The NBG-416N allows the following types of VPN traffic
to pass through:
•
IP security (IPSec)
•
Point-to-Point Tunneling Protocol (PPTP)

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