ZyXEL Communications 110, 1100, 310 13.3 NAT Technical Reference, Ports, Mapped IP, Mapped IP, Mapping Type

	Chapter 13 NAT
Table 84 Configuration > Network > NAT > Add (continued)
LABEL	DESCRIPTION
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	Enable NAT loopback to allow users connected to any interface (instead of just the
Loopback	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).

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.

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ZyWALL 110/310/1100 Series User’s Guide