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Cisco ASA Series Firewall ASDM Configuration Guide
Chapter6 Configuring NAT (ASA 8.2 and Earlier)
NAT Overview
For example, if you want to provide a single address for remote users to access FTP, HTTP, and SMTP,
but these are all actually different servers on the real network, you can specify static PAT statements for
each server that uses the same mapped IP address, but different ports (see Figure6-8).
Figure6-8 Static PAT
You can also use static PAT to translate a well-known port to a non-standard port or vice versa. For
example, if inside web servers use port 8080, you can allow outside users to connect to port 80, and then
undo translation to the original port 8080. Similarly, to provide extra security, you can tell web users to
connect to non-standard port 6785, and then undo translation to port 80.
Bypassing NAT When NAT Control is Enabled
If you enable NAT control, then inside hosts must match a NAT rule when accessing outside hosts. If
you do not want to perform NAT for some hosts, then you can bypass NAT for those hosts or you can
disable NAT control. You might want to bypass NAT, for example, if you are using an application that
does not support NAT. See the “When to Use Application Protocol Inspection” section on page10-2 for
information about inspection engines that do not support NAT.
You can configure traffic to bypass NAT using one of three methods. All methods achieve compatibility
with inspection engines. However, each method offers slightly different capabilities, as follows:
•Identity NAT—When you configure identity NAT (which is similar to dynamic NAT), you do not
limit translation for a host on specific interfaces; you must use identity NAT for connections through
all interfaces. Therefore, you cannot choose to perform normal translation on real addresses when
you access interface A, but use identity NAT when accessing interface B. Regular dynamic NAT, on
Host
Outside
Inside
Undo Translation
10.1.2.27209.165.201.3:21
Undo Translation
10.1.2.28209.165.201.3:80
Undo Translation
10.1.2.29209.165.201.3:25
FTP server
10.1.2.27
HTTP server
10.1.2.28
SMTP server
10.1.2.29
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