Cisco Systems UBR924 Manual De Usuario
3-10
Cisco uBR924 Software Configuration Guide
OL-0337-05 (8/2002)
Chapter 3
Advanced Data-Only Configurations
NAT/PAT Configuration with DHCP Proxy
access-list 1 permit 192.168.1.0 0.0.0.255
!
!
line con 0
line vty 0 4
login
!
end
Note
The above configuration assumes that the DHCP server assigns an IP address to the cable interface that
is in the class C private network (192.168.0.0).
is in the class C private network (192.168.0.0).
Using NAT and DHCP Proxy and Copying Configuration Files
Most service providers typically create a standard configuration file for their cable modems, verify it,
and then copy the working configuration as needed to other cable modems. This can cause problems with
Cisco uBR924 cable access router when using the cable-modem dhcp-proxy command to create a NAT
address pool for NAT/PAT translation.
and then copy the working configuration as needed to other cable modems. This can cause problems with
Cisco uBR924 cable access router when using the cable-modem dhcp-proxy command to create a NAT
address pool for NAT/PAT translation.
The reason is that the default router configuration is for DOCSIS-compliant bridging, which includes
two bridge-group 59 commands for each interface. To use the cable-modem dhcp-proxy command,
you must put the router into routing mode, which means removing the bridge-group commands with the
equivalent no bridge-group commands.
two bridge-group 59 commands for each interface. To use the cable-modem dhcp-proxy command,
you must put the router into routing mode, which means removing the bridge-group commands with the
equivalent no bridge-group commands.
However, because no bridge-group is the default for these CLI commands, they are not saved in the
running configuration. So when you save the Cisco IOS configuration file and copy it to other
Cisco uBR924 cable access router, the router is only partially configured for routing mode and
continually resets its interfaces.
running configuration. So when you save the Cisco IOS configuration file and copy it to other
Cisco uBR924 cable access router, the router is only partially configured for routing mode and
continually resets its interfaces.
In addition, whenever you use the cable-modem dhcp-proxy command to create a NAT pool, the router
automatically adds the appropriate ip nat pool commands to the configuration when it receives the actual
IP addresses from the DHCP server. The IP addresses specified in this command are particular to each
user and should not be copied to other routers.
automatically adds the appropriate ip nat pool commands to the configuration when it receives the actual
IP addresses from the DHCP server. The IP addresses specified in this command are particular to each
user and should not be copied to other routers.
To avoid this problem, use the following procedure to create a Cisco IOS configuration file that uses the
cable-modem dhcp-proxy command to create a NAT address pool for NAT/PAT address translation:
cable-modem dhcp-proxy command to create a NAT address pool for NAT/PAT address translation:
Step 1
Create and test a working configuration on a Cisco uBR924 cable access router.
Step 2
After you have created a standardized configuration, save it to memory, and then copy the Cisco IOS
configuration file to the TFTP server that will be used to copy the file to the other cable access routers.
configuration file to the TFTP server that will be used to copy the file to the other cable access routers.
Step 3
Open the Cisco IOS configuration file with a text editor and add the following lines underneath each
interface:
interface:
no bridge-group 59
no bridge-group 59 spanning-disabled
Step 4
Remove the ip nat pool command.
For example, the following are the relevant lines in a typical DHCP proxy NAT configuration for the
Cisco uBR924 cable access router:
Cisco uBR924 cable access router:
interface Ethernet0
ip address 192.168.1.1 255.255.255.0
ip nat inside