masqurade nat cisco using overloading

Prerequerties
Read the article guncyber-net.blogspot.com/2012/11/masqurade-nat-on-cisco-router.html first

This is simple example for overloading :
================================================================
interface ethernet 0
 ip address 10.10.10.1 255.255.255.0
 ip nat inside

!--- Defines Ethernet 0 with an IP address and as a NAT inside interface.


interface ethernet 1
 ip address 10.10.20.1 255.255.255.0
 ip nat inside

!--- Defines Ethernet 1 with an IP address and as a NAT inside interface.


interface serial 0
 ip address 172.16.10.64 255.255.255.0
 ip nat outside

!--- Defines serial 0 with an IP address and as a NAT outside interface.


ip nat pool ovrld 172.16.10.1 172.16.10.1 prefix 24
 !

!--- Defines a NAT pool named ovrld with a range of a single IP
!--- address, 172.16.10.1.


ip nat inside source list 7 pool ovrld overload
 !
 !
 !
 !

!--- Indicates that any packets received on the inside interface that
!--- are permitted by access-list 7 has the source address
!--- translated to an address out of the NAT pool named ovrld.
!--- Translations are overloaded, which allows multiple inside
!--- devices to be translated to the same valid IP address.


access-list 7 permit 10.10.10.0 0.0.0.31
access-list 7 permit 10.10.20.0 0.0.0.31

!--- Access-list 7 permits packets with source addresses ranging from
!--- 10.10.10.0 through 10.10.10.31 and 10.10.20.0 through 10.10.20.31

==================================================================

Note: Cisco highly recommends that you do not configure access lists referenced by NAT commands with permit any. Using permit any can result in NAT consuming too many router resources which can cause network problems.

Notice in the previous configuration that only the first 32 addresses from subnet 10.10.10.0 and the first 32 addresses from subnet 10.10.20.0 are permitted by access-list 7. Therefore, only these source addresses are translated. There may be other devices with other addresses on the inside network, but these are not translated.