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Configuring Subscriber-End Broadband Access Router Features
Customizing the Cable Access Router Interface
MC-649
Cisco IOS Multiservice Applications Configuration Guide
Customizing the Cable Access Router Interface
Different geographical regions and different cable plants use different frequency bands. The
Cisco uBR900 series cable access router uses a built-in default frequency scanning feature to address
this issue. After the cable access router finds a successful downstream frequency channel, it saves the
channel and power setting to NVRAM. The cable access router recalls this value the next time it needs
to synchronize its frequency or register with the cable service provider CMTS.
However, you can customize the cable access router interface configuration if you need to deviate from
the default setting that ships with the unit. For example, you might need to specify a different compliant
mode, modify the saved downstream channel setting and upstream power value, or enable a faster
downstream search algorithm.
Note Most cable network scenarios will not require you to use the commands in this section.
To customize the cable access router interface, use the following commands beginning in global
configuration mode:
Using Multiple PCs with the Cable Access Router
The MAX CPE parameter in the DOCSIS configuration file determines how many PCs or other CPE
devices are supported by a particular cable access router. The default value for the MAX CPE parameter
is 1, which means only one PC can be connected to the cable access router unless this value is changed.
The DOCSIS 1.0 specification states that a CMTS cannot age out MAC addresses for CPE devices. Thus,
if MAX CPE = 1, the first PC that is connected to a cable access router is normally the only one that the
CMTS recognizes as valid. If you wish to replace an existing PC or change its network interface card
(NIC) to one that has a different MAC address, the CMTS will refuse to let the PC come online because
this would exceed the maximum number of CPE devices specified by the MAX CPE parameter.
If you wish to replace an existing PC or NIC, use one of the following workarounds:
• Use the clear cable host reset command on the Cisco uBR7200 series universal broadband router
to remove the PC MAC address from the router internal address tables. The PC MAC address will
be rediscovered and associated with the correct cable access router during the next DHCP lease
cycle.
Command Purpose
Step 1
uBR924(config)# interface cable-modem 0
Specifies cable access router interface 0.
Step 2
uBR924(config-if)# cable-modem compliant bridge
Enables DOCSIS-compliant bridging.
Step 3
uBR924(config-if)# cable-modem downstream saved
channel ds-frequency us-power
Modifies the saved downstream channel setting and
upstream power value. If you do this, you must
specify an exact downstream frequency and a power
value.
1
1. Use the no cable-modem downstream saved channel ds-frequency us-power command to remove a saved frequency and power setting from
NVRAM.
Step 4
uBR924(config-if)# cable-modem fast-search
Enables a faster downstream search algorithm.