Nat Examples; Overlapping Networks - Cisco PIX 500 Series Configuration Manual

NAT Examples

To exempt an inside address when accessing two different destination addresses, enter the following
commands:
hostname(config)# access-list NET1 permit ip 10.1.2.0 255.255.255.0 209.165.201.0
255.255.255.224
hostname(config)# access-list NET1 permit ip 10.1.2.0 255.255.255.0 209.165.200.224
255.255.255.224
hostname(config)# nat (inside) 0 access-list NET1
NAT Examples
This section describes typical scenarios that use NAT solutions, and includes the following topics:
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Overlapping Networks

In Figure
Figure 17-27
192.168.100.2
192.168.100.1
Two networks use an overlapping address space (192.168.100.0/24), but hosts on each network must
communicate (as allowed by access lists). Without NAT, when a host on the inside network tries to access
a host on the overlapping DMZ network, the packet never makes it past the security appliance, which
sees the packet as having a destination address on the inside network. Moreover, if the destination
address is being used by another host on the inside network, that host receives the packet.
To solve this problem, use NAT to provide non-overlapping addresses. If you want to allow access in
both directions, use static NAT for both networks. If you only want to allow the inside interface to access
hosts on the DMZ, then you can use dynamic NAT for the inside addresses, and static NAT for the DMZ
addresses you want to access. This example shows static NAT.
To configure static NAT for these two interfaces, perform the following steps. The 10.1.1.0/24 network
on the DMZ is not translated.
Cisco Security Appliance Command Line Configuration Guide
17-34
Overlapping Networks, page 17-34
Redirecting Ports, page 17-36
17-27, the security appliance connects two private networks with overlapping address ranges.
Using Outside NAT with Overlapping Networks
inside
192.168.100.0/24
192.168.100.3
outside
10.1.1.2
192.168.100.0/24
10.1.1.1
Chapter 17 Configuring NAT
192.168.100.2
dmz
192.168.100.3
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