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Cisco uBR924 Software Configuration Guide
OL-0337-05 (8/2002)
Chapter 3 Advanced Data-Only Configurations
NAT/PAT Configuration with DHCP Proxy
NAT/PAT Configuration with DHCP Proxy
The NAT/PAT feature can also be used with the cable-modem dhcp-proxy nat command, so that the
router obtains the IP address used for the NAT pool for the Ethernet interface from the DHCP server.
This allows the service provider to dynamically provide this IP address in the same manner as for the
cable interface.
In addition to using the the cable-modem dhcp-proxy nat command, you must also use the following
NAT configuration commands:
• Use the ip nat inside interface command to configure the Ethernet interface as the “inside”
interface.
• Use the ip nat outside interface command to configure the cable interface as the “outside” interface.
• Specify the overload option with the ip nat global configuration command because the NAT pool
created by the cable-modem dhcp-proxy command contains only one IP address.
The following commands show a typical configuration. (These steps assume that the router has already
been configured for routing mode, as described in “Data-Only Routing” section on page 3-2.)
Command Purpose
Step 1
UBR924(config)# ip nat inside source list list-id interface
cable-modem0 overload
Enables translation of the inside source
addresses—the “inside” addresses are translated
before being presented to the “outside” network.
The list-id specifies an access-list that defines the IP
addresses that will be used, and overload specifies
that multiple inside IP addresses can use the same
outside IP address (but using different port numbers
to unique identify each inside host).
Step 2
UBR924(config)# interface Ethernet0 Enters interface configuration mode for the router’s
Ethernet interface.
Step 3
UBR924(config-if)# ip nat inside Specifies that the Ethernet is the “inside” of the
NAT/PAT translation.
Step 4
UBR924(config-if)# exit Exits interface configuration mode.
Step 5
UBR924(config)# interface cable-modem0 Enters interface configuration mode for the router’s
cable interface.
Step 6
UBR924(config-if)# cable-modem dhcp-proxy nat
pool-name
Specifies the name of the NAT pool to be created
using the IP address and subnet mask supplied by the
DHCP server. The pool-name can be any arbitrary
string.
Note This is equivalent to giving the ip nat pool
command, using the IP address and subnet
mask supplied by the DHCP server.
Step 7
UBR924(config-if)# ip nat outside Specifies that the cable interface is the “outside” of
the NAT/PAT translation.
Step 8
UBR924(config-if)# exit Exits interface configuration mode.