NAT
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Simple NAT Overload to share the WAN connection
Router1(config)#access-list 1 permit 10.0.0.0 0.255.255.255 Router1(config)#ip nat inside source list 1 interface FastEthernet 0/0 overload Router1(config)#interface FastEthernet0/0 Router1(config-if)#ip nat outside Router1(config-if)#interface FastEthernet0/1 Router1(config-if)#ip nat inside