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NAT Configurations 347
The change to the configuration is extremely minor; an extra argument was added to the simple
NAT translation. However, in an overload configuration, only a single IP address is needed to
front for a large number of clients.
NAT Overlapping Configuration
NAT can deal with overlapping networks, even though it is not desirable to create an overlapped
network. The overlapping of networks typically occurs during a merger of two companies that
are using the same private address space. The overlap configuration is put in place as a stopgap
while renumbering takes place.
The following configuration uses the addresses designated as Outside Global and Outside Local
with reference, albeit arbitrary, to one or the other networks. One network is declared as the
inside space and one is declared as the outside space.
Figure 11-7 shows a scenario in which two networks that are both using the 10.0.0.0 address
space are merged using an overlap configuration. It should be pointed out that the same overall
effect could be accomplished by doing a simple translation on the edge router and leaving each
of the networks intact; however, with the overlap configuration, the translation is done on one
router platform only. This provides a single point for the configuration and a single point for
maintenance of the address space.
!declare inside interfaces
interface e0
ip address 10.0.0.1 255.255.255.0
ip nat inside
!declare outside interface
interface s0
ip address 144.14.14.1 255.255.255.0
ip nat outside
Example 11-3
NAT Overload Implementation (Continued)