Other client of other interface serial, trying to connect with our server 192.168.1.1:

   |  Source   - destination |                    | Source   - destination     | 
   | ip client - 192.168.1.1 | --> |   X    | --> |ip client NAT - 192.168.1.1 |
                                   | router |  
 |  Source     - destination |     |        |     | Source      - destination   |  
 | 10.12.0.170 -  ipclient   | <-- |        | <-- | 192.168.1.1 - ip client NAT |



- = - = - = - = - = - = - = - = - = - = - = - = - = - = - = - = - = - = - = - = - = - = - = - = - = -



                   +--------+           | 
        serial 2/1 |        |           |
  -----------------|        | fas 0/0   |    +--------+    |     192.168.1.1
                   | router |-----------|    |        |    |    +--------+
        serial 2/4 |        |           |----|        |----|    |        |
  -----------------|        |           |    |   FW   |    |----| server |
                   |        |           |    |        |    |    +--------+
        serial 3/5 |        |                +--------+
  -----------------|        |
                   |        |
                   +--------+


interface FastEthernet0/0
 ip address 10.145.107.131 255.255.255.0
 ip nat inside

interface Serial1/1
 description client 1
 ip nat outside
 ip address 192.168.117.1 255.255.255.0
!
interface Serial1/2
 description description client 2
 ip address 192.168.127.1 255.255.255.0
 ip nat outside
!
interface Serial3/5
 description description client 3
ip address 192.168.151.1 255.255.255.0 
 ip nat outside
!

ip nat pool client-1 10.10.117.1 10.10.117.254 netmask 255.255.255.0
ip nat pool client-2 10.10.127.1 10.10.127.254 netmask 255.255.255.0
ip nat pool client-3 10.10.151.1 10.10.151.254 netmask 255.255.255.0
!
ip nat outside source list 1 pool client-1
ip nat outside source list 2 pool client-2
ip nat outside source list 3 pool client-3
!
access-list 1 permit 172.16.16.0 0.0.0.255
access-list 2 permit 172.17.17.0 0.0.0.255
access-list 3 permit 172.18.18.0 0.0.0.255

ip nat pool PROBLEMA 10.12.0.170 10.12.0.170 netmask 255.255.255.0 
ip nat inside source list 50 pool PROBLEMA 
access-list 50 permit 192.168.1.1