NAT allows organizations to resolve the problem of IP address depletion when they have existing networks and must access the
Internet. Sites that do not yet possess Network Information Center (NIC)-registered IP addresses must acquire them. If more
than 254 clients are present or planned, the scarcity of Class B addresses becomes a serious issue. Cisco IOS XE NAT addresses
these issues by mapping thousands of hidden internal addresses to a range of easy-to-get Class C addresses.
Sites that already have registered IP addresses for clients on an internal network may want to hide those addresses from the
Internet. This action disable hacker to directly attack the clients. With clients addresses hidden, an extent of security
is established. Cisco IOS XE NAT gives LAN administrators complete freedom to expand Class A addressing. The Class A addressing
expansion is drawn from the reserve pool of the Internet Assigned Numbers Authority (RFC 1597). This expansion occurs within
the organization without concern for addressing changes at the LAN/Internet interface.
The Cisco IOS XE software can selectively or dynamically perform NAT. This flexibility allows the network administrator to
use a mix of RFC 1597 and RFC 1918 addresses or registered addresses. NAT is designed for use on various devices for IP address
simplification and conservation. In addition, Cisco IOS XE NAT allows the selection of internal hosts that are available for
A significant advantage of NAT is that it can be configured without requiring changes to hosts or devices in the network.
However, changes are required on few other devices where NAT is configured.
In Cisco IOS XE Denali 16.3 release, Multi-Tenant support for NAT feature was introduced. With Multi-Tenant support, the configuration
changes of a Virtual Routing and Forwarding (VRF) instance does not interrupt the traffic flow of other VRFs in the network.
NAT is a feature that allows the IP network of an organization to appear, from the outside, to be using a different IP address
space than the one that it is actually using. Thus, NAT allows an organization with nonglobally routable addresses to connect
to the Internet by translating those addresses into a globally routable address space. NAT also allows a graceful renumbering
strategy for organizations that are changing service providers or voluntarily renumbering into classless interdomain routing
(CIDR) blocks. NAT is described in RFC 1631.