Hi,
You need to configure PAT (Port address translation) rather than simple NAT. Cisco reffers to this as NAT Overload I think. It is done in a slightly different way. The idea is that if you have only one ip address (like you) of an interface with public IP, you create an acl which devices may use such a address to access outside the network. Then these devices will access outer networks by single private IP of the overloaded interface, but different ports.
It is configured like this:
First you create the standard access-list to define which hosts may use that public ip address in translation.
Router(config)#access-list NUMBER_OF_ACL permit source [source-wildcard]
Then you link that access-list to specific interface and with the word overload you specify that you want to enable port address translation.
Router(config)#ip nat inside source list NUMBER_OF_ACL interface YOUR_INTERFACE overload
Then - as usual - you just specify the inside and outside interfaces.
Router(config)#interface YOUR_INSIDE_INTERFACE
Router(config-if)#ip nat inside
Router(config)#interface YOUR_OUTSIDE_INTERFACE
Router(config-if)#ip nat outside
In addition: If you would have been given more public IP addresses - you can consider using the other method.
When using the other method you omit the command
Router(config)#ip nat inside source list NUMBER_OF_ACL interface YOUR_INTERFACE overload
and add following two instead(the rest of commands are the same):
To specify the pool of public IP adresses you have been given for translation
Router(config)#ip nat pool NAME START-IP END-IP
To enable port address translation
Router(config)#ip nat inside source list ACL-NUMBER pool NAME overload
As I said, the rest of commands are the same as in the first method written above. Just omit the one I have written and add these two instead.
Hope that helps!
Best regards,
Jan.
