Hello,
this is a sample config off CCO, check the link below for the entire document (you might need a CCO logon):
The following configuration for the Cisco uBR905 and Cisco uBR925 cable access routers shows an example of a cable access router in routing mode that performs NAT/PAT translation on all IP addresses connected to the router's Ethernet interface. The external IP address is overloaded so that multiple IP addresses on the internal network can use the same external IP address over the cable interface. Different port numbers are used to uniquely identify each device on the Ethernet interface. The relevant commands are shown in bold.
version 12.1
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname Router
!
!
ip nat inside source list 1 interface cable-modem0 overload
clock timezone - -4
!
!
interface Ethernet0
ip address 192.168.1.1 255.255.255.0
ip nat inside
!
interface cable-modem0
ip nat outside
no cable-modem compliant bridge
!
ip routing
ip default-gateway 10.1.1.1
ip classless
no ip http server
no service finger
ip route 0.0.0.0 0.0.0.0 10.1.1.1
access-list 1 permit 192.168.1.0 0.0.0.255
!
!
line con 0
line vty 0 4
login
!
end
Cisco uBR905/uBR925 Cable Access Router Software Configuration Guide
Chapter 3 - Advanced Data-Only Configurations
http://www.cisco.com/en/US/products/hw/cable/ps2221/products_configuration_guide_chapter09186a008007cf8f.html
HTH,
GP
