Configure IP for WAN & LAN interfaces
ip address 202.xxx.xxx.x 255.255.255.240
ip address 192.168.100.1 255.255.255.0
Define outside interface for NAT (WAN)
R1(config)#interface serial0/x
R1(config-if)# ip nat outside
Define inside interface for NAT (LAN)
R1(config)#interface gi0/x
R1(config-if)# ip nat inside
Create an Access Control List (ACL) that will include local (private) hosts or network(s) to be translated
R1(config)#access-list 100 permit ip 192.168.x.0 0.0.0.255 any
Finally enable NAT overload to WAN interface with the above ACL
R1(config)#ip nat inside source list 100 interface serial0/x overload
Verify NAT overload operation
R1#show ip nat translations
Clear NAT table to free up resources
R1#clear ip nat translation *
show NAT statistics
R1#show ip nat statistics