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321
C
HAPTER
17
NAT
17.1
NAT Overview
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. Use Network Address Translation (NAT) to make computers on a
private network behind the ZyWALL available outside the private network. If the
ZyWALL has only one public IP address, you can make the computers in the
private network available by using ports to forward packets to the appropriate
private IP address.
Suppose 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 191
Multiple Servers Behind NAT Example
17.1.1
What You Can Do in this Chapter
Use the
NAT
screens (see
Section 17.2 on page 322
) to view and manage the list
of NAT rules and see their configuration details. You can also create new NAT rules
and edit or delete existing ones.
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17.1.2
What You Need to Know
NAT is also known as virtual server, port forwarding, or port translation.
Finding Out More
See
Section 6.5.10 on page 99
for related information on these screens.
See
Section 17.3 on page 327
for technical background information related to
these screens.
See
Section 7.9.2 on page 140
for an example of how to configure NAT to allow
H.323 traffic from the WAN to the LAN.
See
Section 7.10.2 on page 144
for an example of how to configure NAT to allow
web traffic from the WAN to a server on the DMZ.
See
Section 7.11.3 on page 149
for an example of how to configure NAT to allow
SIP traffic from the WAN to an IPPBX or SIP server on the DMZ.
17.2
The NAT Screen
The
NAT
summary screen provides a summary of all NAT rules and their
configuration. In addition, this screen allows you to create new NAT rules and edit
and delete existing NAT rules. To access this screen, login to the Web Configurator
and click
Configuration > Network > NAT
. The following screen appears,
providing a summary of the existing NAT rules.
Figure 192
Configuration > Network > NAT
The following table describes the labels in this screen.
Table 92
Configuration > Network > NAT
LABEL
DESCRIPTION
Add
Click this to create a new entry.
Edit
Double-click an entry or select it and click
Edit
to open a screen where
you can modify the entry’s settings.
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Remove
To remove an entry, select it and click
Remove
. The ZyWALL confirms
you want to remove it before doing so.
Activate
To turn on an entry, select it and click
Activate
.
Inactivate
To turn off an entry, select it and click
Inactivate
.
#
This field is a sequential value, and it is not associated with a specific
entry.
Status
This icon is lit when the entry is active and dimmed when the entry is
inactive.
Name
This field displays the name of the entry.
Mapping Type
This field displays what kind of NAT this entry performs:
Virtual Server
,
1:1 NAT
, or
Many 1:1 NAT
.
Interface
This field displays the interface on which packets for the NAT entry are
received.
Original IP
This field displays the original destination IP address (or address object)
of traffic that matches this NAT entry. It displays
any
if there is no
restriction on the original destination IP address.
Mapped IP
This field displays the new destination IP address for the packet.
Protocol
This field displays the service used by the packets for this NAT entry. It
displays
any
if there is no restriction on the services.
Original Port
This field displays the original destination port(s) of packets for the NAT
entry. This field is blank if there is no restriction on the original
destination port.
Mapped Port
This field displays the new destination port(s) for the packet. This field is
blank if there is no restriction on the original destination port.
Apply
Click this button to save your changes to the ZyWALL.
Reset
Click this button to return the screen to its last-saved settings.
Table 92
Configuration > Network > NAT (continued)
LABEL
DESCRIPTION
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17.2.1
The NAT Add/Edit Screen
The
NAT Add/Edit
screen lets you create new NAT rules and edit existing ones.
To open this window, open the
NAT
summary screen. (See
Section 17.2 on page
322
.) Then, click on an
Add
icon or
Edit
icon to open the following screen.
Figure 193
Configuration > Network > NAT > Add
The following table describes the labels in this screen.
Table 93
Configuration > Network > NAT > Add
LABEL
DESCRIPTION
Create new
Object
Use to configure any new settings objects that you need to use in this
screen.
Enable Rule
Use this option to turn the NAT rule on or off.
Rule Name
Type in the name of the NAT rule. The name is used to refer to the NAT
rule. You may use 1-31 alphanumeric characters, underscores(
_
), or
dashes (-), but the first character cannot be a number. This value is
case-sensitive.
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Classification
Select what kind of NAT this rule is to perform.
Virtual Server
- This makes computers on a private network behind the
ZyWALL available to a public network outside the ZyWALL (like the
Internet).
1:1 NAT
- If the private network server will initiate sessions to the
outside clients, select this to have the ZyWALL translate the source IP
address of the server’s outgoing traffic to the same public IP address
that the outside clients use to access the server.
Many 1:1 NAT -
If you have a range of private network servers that will
initiate sessions to the outside clients and a range of public IP addresses,
select this to have the ZyWALL translate the source IP address of each
server’s outgoing traffic to the same one of the public IP addresses that
the outside clients use to access the server. The private and public
ranges must have the same number of IP addresses.
One many 1:1 NAT rule works like multiple 1:1 NAT rules, but it eases
configuration effort since you only create one rule.
Incoming
Interface
Select the interface on which packets for the NAT rule must be received.
It can be an Ethernet, VLAN, bridge, or PPPoE/PPTP interface.
Original IP
Specify the destination IP address of the packets received by this NAT
rule’s specified incoming interface.
any
- Select this to use all of the incoming interface’s IP addresses
including dynamic addresses or those of any virtual interfaces built upon
the selected incoming interface.
User Defined
- Select this to manually enter an IP address in the
User
Defined
field. For example, you could enter a static public IP assigned
by the ISP without having to create a virtual interface for it.
Host address - select a host address object to use the IP address it
specifies. The list also includes address objects based on interface IPs.
So for example you could select an address object based on a WAN
interface even if it has a dynamic IP address.
User Defined
Original IP
This field is available if
Original IP
is
User Defined
. Type the
destination IP address that this NAT rule supports.
Original IP
Subnet/Range
This field displays for Many 1:1 NAT. Select the destination IP address
subnet or IP address range that this NAT rule supports. The original and
mapped IP address subnets or ranges must have the same number of IP
addresses.
Mapped IP
Select to which translated destination IP address this NAT rule forwards
packets.
User Defined
- this NAT rule supports a specific IP address, specified in
the
User Defined
field.
HOST address - the drop-down box lists all the HOST address objects in
the ZyWALL. If you select one of them, this NAT rule supports the IP
address specified by the address object.
User Defined
Original IP
This field is available if
Mapped IP
is
User Defined
. Type the translated
destination IP address that this NAT rule supports.
Table 93
Configuration > Network > NAT > Add (continued)
LABEL
DESCRIPTION

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