Specifications

Table Of Contents

Release Notes for Cisco uBR904 Cable Access Router for Cisco IOS Release 12.0(7)T 11

Limitations and Restrictions

This section describes warnings and cautions about using Cisco IOS Release 12.0 T software.

Using Multiple PCs with a Cisco uBR904 Cable Access Router

The MAX CPE parameter in a Cisco uBR904 cable access router’s DOCSIS conﬁguration ﬁle

determines how many PCs (or other CPE devices) are supported by that Cisco uBR904 cable access

router. The default value for the MAX CPE parameter is 1, which means only one PC can be

connected to the Cisco uBR904 cable access router.

The DOCSIS 1.0 speciﬁcation states that a CMTS cannot age-out MAC addresses for CPE devices,

so the ﬁrst PC that is connected to the Cisco uBR904 cable access router is normally the only one

that the CMTS recognizes as valid. If a subscriber replaces an existing PC or changes 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.

To allow a subscriber to replace an existing PC or NIC, the following workarounds are possible:

• If using a Cisco uBR7200 series router as the CMTS, enter the clear cable host MAC address

command on the Cisco uBR7200 series router to remove the PC’s MAC address from the router’s

internal address tables. The PC’s MAC address will be rediscovered and associated with the

correct Cisco uBR904 cable access router during the next DHCP lease cycle.

• Increase the value of the MAX CPE parameter in the Cisco uBR904 cable access router’s

DOCSIS conﬁguration ﬁle so that it can accommodate the desired number of PCs. Reset the

Cisco uBR904 cable access router to force it to load the new conﬁguration ﬁle.

Bridging Mode

The Cisco uBR904 cable access router ships from the Cisco factory with the console port enabled.

Based on the standard practices in place for your network, disable the console port as appropriate

via the DOCSIS conﬁguration ﬁle downloaded to the Cisco uBR904 cable access router. This

prohibits network conﬁguration access at the remote site.

Note Downloading a Cisco IOS image disables the console port by default and erases all previously

saved conﬁgurations.

For software enhancements when operating in bridging mode, see the “Enhancements to Bridging

Operation” section of the New Software Features in Release 12.0(5)T.

The ability of the Cisco uBR904 cable access router to grant access to customer premises equipment

(CPE) devices is controlled by the “MAX CPE” ﬁeld in the DOCSIS conﬁguration ﬁle. The

Cisco uBR904 cable access router defaults to one CPE MAC address unless this option is set to a

higher number. The valid range using Cisco IOS Release 12.0(5)T or higher images is 1 to 254 for

bridging operation; 1 ﬁlter is reserved for the broadcast address.

You can install and conﬁgure the Cisco uBR904 cable access router to operate as a router. In routing

mode, no maximum upper limitation exists. For instructions to change from bridging to routing

mode, see the “Important Notes” section on page 12.