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Cisco ASA Series Firewall CLI Configuration Guide
Chapter3 Information About NAT
NAT Types
Figure 3-5 shows a typical many-to-few static NAT scenario.
Figure3-5 Many-to-Few Static NAT
Instead of using a static rule this way, we suggest that you create a one-to-one rule for the traffic that
needs bidirectional initiation, and then create a dynamic rule for the rest of your addresses.
Dynamic NAT
This section describes dynamic NAT and includes the following topics:
•Information About Dynamic NAT, page3-7
•Dynamic NAT Disadvantages and Advantages, page3-8

Information About Dynamic NAT

Dynamic NAT translates a group of real addresses to a pool of mapped addresses that are routable on the
destination network. The mapped pool typically includes fewer addresses than the real group. When a
host you want to translate accesses the destination network, the ASA assigns the host an IP address from
the mapped pool. The translation is created only when the real host initiates the connection. The
translation is in place only for the duration of the connection, and a given user does not keep the same
IP address after the translation times out. Users on the destination network, therefore, cannot initiate a
reliable connection to a host that uses dynamic NAT, even if the connection is allowed by an access rule.
Figure 3-6 shows a typical dynamic NAT scenario. Only real hosts can create a NAT session, and
responding traffic is allowed back.
Figure3-6 Dynamic NAT
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