The first three NAT examples in this section are based on the
following topology:
Based on this topology, there are three NAT policies we need
to create as follows:
To enable the clients on the internal network to access
resources on the Internet, the internal 192.168.1.0 addresses will
need to be translated to publicly routable addresses. In this case,
we will configure source NAT (the purple enclosure and arrow above),
using the egress interface address, 203.0.113.100, as the source
address in all packets that leave the firewall from the internal
zone. See Translate
Internal Client IP Addresses to Your Public IP Address (Source DIPP
NAT) for instructions.
To enable clients on the internal network to access the public
web server in the DMZ zone, we must configure a NAT rule that redirects
the packet from the external network, where the original routing
table lookup will determine it should go based on the destination
address of 203.0.113.11 within the packet, to the actual address
of the web server on the DMZ network of 10.1.1.11. To do this you
must create a NAT rule from the trust zone (where the source address
in the packet is) to the untrust zone (where the original destination
address is) to translate the destination address to an address in
the DMZ zone. This type of destination NAT is called U-Turn
NAT (the yellow enclosure and arrow above). See Enable
Clients on the Internal Network to Access your Public Servers (Destination
U-Turn NAT) for instructions.
To enable the web server—which has both a private IP address
on the DMZ network and a public-facing address for access by external users—to
both send and receive requests, the firewall must translate the
incoming packets from the public IP address to the private IP address
and the outgoing packets from the private IP address to the public
IP address. On the firewall, you can accomplish this with a single
bi-directional static source NAT policy (the green enclosure and
arrow above). See Enable
Bi-Directional Address Translation for Your Public-Facing Servers
(Static Source NAT).
Refer to additional NAT configuration examples that apply to your setup: