168.1.94 255.255.255.0
ip nat inside
!
access-list 1 permit 192.168.1.0 0.0.0.255
Host A
192.168.1.100
E0
192.168.1.94
S0
171.69.232.182
Host B
192.168.1.101
Host C
10.1.1.1
Host D
172.16.1.1
258 Chapter 7: Managing Address Spaces with NAT and IPv6
Overloading an Inside Global Address
You can conserve addresses in the inside global address pool by allowing the router to
use one inside global address for many inside local addresses. When this overloading is
con?¬?gured, the router maintains enough information from higher-level protocols??”for
example, TCP or User Datagram Protocol (UDP) port numbers??”to translate the inside
global address back into the correct inside local address. When multiple inside local
addresses map to one inside global address, the TCP or UDP port numbers of each inside
host distinguish between the local addresses.
Figure 7-6 illustrates NAT operation when one inside global address represents multiple
inside local addresses. The TCP port numbers act as differentiators.
Figure 7-6 Overloading an Inside Global Address
Both host B and host C think they are talking to a single host at address 2.2.2.2. They are
actually talking to different hosts; the port number is the differentiator.
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