Network Address Translation (NAT) is the translation of source and/or destination IP addresses. The reasons to use this can be:
• Lack of address space
• Migration of network(s)
• Security
The following types of NAT are used by Cisco:
• Static NAT
• Dynamic NAT
• Overloading
Static NAT
Mapping an (unregistered) IP address to a (registered) IP address on a one-to-one basis.
Dynamic NAT
Maps an unregistered IP address to a registered IP address from a group of registered IP addresses.
Overloading
A form of dynamic NAT that maps multiple unregistered IP addresses to a single registered IP address by using different ports. Known also as PAT (Port Address Translation) or hide NAT.
At least two interfaces are necessary for a NAT configuration. One inside interface and one outside interface.
The following addresses are known by a Cisco NAT configuration:
• Inside Local
• Inside Global
• Outside Local
• Outside Global
Inside Local
A local host is known from the inside by the inside local IP address.
Inside Global
A local host is known from the outside by the inside global IP address.
Outside Local
A local host is known from the outside by the outside global IP address.
Outside Global
An outside host is known from the outside by the outside global IP address.
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