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Network Address Translation
83
Figure 23 provides an example of static port mapping. TCP port 81 of the web server at private address 192.168.1.6 is mapped
to the same TCP port of the public address.
Figure 23 Mapping Ports
12.1.4Configuration for Figure 2
Blackbox> configure terminal
Blackbox/configure> interface bundle Trenton
Blackbox/configure/interface/bundle Trenton> nat
Blackbox/configure/interface/bundle Trenton/nat> enable dynamic
Blackbox/configure/interface/bundle Trenton/nat> enable static
Blackbox/configure/interface/bundle Trenton/nat> address 192.168.1.6 81 100.1.1.6 81
12.1.5 Reverse NAT
Reverse NAT could be used in a situation where one LAN is using private RFC 1918 IP addresses and a second LAN is using
“real” Internet routable IP addresses. Figure 24 illustrates how reverse NAT would be applied.
Internet
Workstation
192.168.1.1/24
Workstation
192.168.1.2/24
Workstation
192.168.1.3/24
Workstation
192.168.1.5/24
FTP, SMTP, HTTP Server
192.168.1.6/24
10/100 BaseT Ethernet
100.1.1.1/29
192.168.1.254/24
www server is runnin
g
on TCP port 81