Abrer_Wiki

Static NAT requires few configuration steps. Each static mapping between local and global addresses must be configured. Not unlike a static entry for every static IP address required. You must inform the router on which interfaces to use NAT. Interface subcommands inform the router which interfaces are inside / outside.

1. ip nat inside command on an interface to specify inside.
2. ip nat outside command on an interface to specify outside.
3. ip nat inside source static inside-local inside-global from global config to configure the static mappings.
4. inside local will be a LAN IP - inside global will be your public IP (an EXTRA public IP).

Create an access list to match a group of source addresses as needed – why else would we overload?

R1(config-std-nacl)#permit 10.1.1.0 0.0.0.255

R1#sh access-lists 
Standard IP access list NAT
    10 permit 10.1.1.0, wildcard bits 0.0.0.255 (2 matches)
    20 deny   any

ip nat inside source list MY_LIST int fa0/0 OVERLOAD