关键语句
!ACCESS-GROUP FOR WAN INTERFACE
ip access-list extended IN_ACL
permit tcp any any eq 143 log
!ACL TO MATCH THE FLOW
ip access-list extended REVERSE_PROXY
permit tcp any any eq 143
!FastEthernet0/0 is a LAN interface
ip nat source list REVERSE_PROXY interface FastEthernet0/0 overload
!NAT PORT MAPPING TO WAN FastEthernet0/1
ip nat source static tcp 192.168.4.X 143 interface FastEthernet0/1 143
!NAT client's source ip to the ip of LAN interface
ip nat source list REVERSE_PROXY interface FastEthernet0/0 overload
