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Chapter 13 NAT
ZyWALL 110/310/1100 Series User’s Guide
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13.3 NAT Technical Reference
Here is more detailed information about NAT on the ZyWALL.
NAT Loopback
Suppose an NAT 1:1 rule maps a public IP address to the private IP address of a LAN SMTP e-mail
server to give WAN users access. NAT loopback allows other users to also use the rule’s original IP
to access the mail server.
For example, a LAN user’s computer at IP address 192.168.1.89 queries a public DNS server to
resolve the SMTP server’s domain name (xxx.LAN-SMTP.com in this example) and gets the SMTP
server’s mapped public IP address of 1.1.1.1.
Mapped End Port This field is available if Mapping Type is Ports. Enter the end of the range of
translated destination ports if this NAT rule forwards the packet. The original port
range and the mapped port range must be the same size.
Enable NAT
Loopback Enable NAT loopback to allow users connected to any interface (instead of just the
specified Incoming Interface) to use the NAT rule’s specified Original IP address to
access the Mapped IP device. For users connected to the same interface as the
Mapped IP device, the ZyWALL uses that interface’s IP address as the source address
for the traffic it sends from the users to the Mapped IP device.
For example, if you configure a NAT rule to forward traffic from the WAN to a LAN
server, enabling NAT loopback allows users connected to other interfaces to also
access the server. For LAN users, the ZyWALL uses the LAN interface’s IP address as
the source address for the traffic it sends to the LAN server. See
NAT Loopback on
page 225 for more details.
If you do not enable NAT loopback, this NAT rule only applies to packets received on
the rule’s specified incoming interface.
Firewall By default the firewall blocks incoming connections from external addresses. After you
configure your NAT rule settings, click the Firewall link to configure a firewall rule to
allow the NAT rule’s traffic to come in.
The ZyWALL checks NAT rules before it applies To-ZyWALL firewall rules, so To-ZyWALL
firewall rules do not apply to traffic that is forwarded by NAT rules. The ZyWALL still
checks other firewall rules according to the source IP address and mapped IP address.
OK Click OK to save your changes back to the ZyWALL.
Cancel Click Cancel to return to the NAT summary screen without creating the NAT rule (if it
is new) or saving any changes (if it already exists).
Table 84
Configuration > Network > NAT > Add (continued)
LABEL DESCRIPTION