Cisco Systems ASA 5585-X Manual De Usuario

You can implement NAT using the following methods:

Static NAT—A consistent mapping between a real and mapped IP address. Allows bidirectional 
traffic initiation. See the 

Dynamic NAT—A group of real IP addresses are mapped to a (usually smaller) group of mapped IP 
addresses, on a first come, first served basis. Only the real host can initiate traffic. See the 

Dynamic Port Address Translation (PAT)—A group of real IP addresses are mapped to a single IP 
address using a unique source port of that IP address. See the 

.

Identity NAT—A real address is statically translated to itself, essentially bypassing NAT. You might 
want to configure NAT this way when you want to translate a large group of addresses, but then want 
to exempt a smaller subset of addresses. See the 

This section describes static NAT and includes the following topics:

Static NAT creates a fixed translation of a real address to a mapped address. Because the mapped address 
is the same for each consecutive connection, static NAT allows bidirectional connection initiation, both 
to and from the host (if an access rule exists that allows it). With dynamic NAT and PAT, on the other 
hand, each host uses a different address or port for each subsequent translation, so bidirectional initiation 
is not supported.