Specifications

Release Notes for Cisco uBR924 Cable Access Router for Cisco IOS Release 12.1(5)T

OL-0385-04 Rev. B0 (2/2001)

Limitations and Restrictions

• Radio Frequency Interface MIBs

• SGCP MIB

Limitations and Restrictions

This section describes warnings and cautions about using Cisco IOS Release 12.1(5)T software.

Bridging Support

The Cisco uBR924 Cable Access Router interoperates with DOCSIS cable networks. Cisco IOS

Release 12.1 T does not support bridging traffic across a non-DOCSIS cable network.

DOCSIS CLI Commands Are Removed

To comply with DOCSIS requirements that restrict access to commands that change DOCSIS

parameters, Cisco IOS Release 12.1(2)T has removed a number of commands from the CLI. These

commands are now reserved exclusively for DOCSIS use. See the description of caveat CSCdr32984,

page 32, for more details.

GRE IP Tunnels Are Not Supported

Generic routing encapsulation (GRE) IP tunnels cannot be built between two Cisco uBR924 Cable

Access Routers because GRE IP tunnels are not supported in any Cisco IOS image for the

Cisco uBR924 Cable Access Routers. IPSec tunnels, however, are supported when using Cisco IOS

images that support IPSec encryption.

IP Address Negotiation

The DOCSIS specifications require that a cable modem obtain its IP address at power-on or reset from

a DHCP server that is available through the cable interface. For this reason, the Cisco uBR924 Cable

Access Router defaults to a configuration that uses the ip address dhcp command for the cable

interface. It is not possible to override this setting by specifying a specific static IP address; to assign a

static IP address to the Cisco uBR924 router, configure the DHCP server so that it assigns the desired

IP address on the basis of the unit’s MAC address. However, service providers should warn subscribers

that changes in the cable network's topology—due to traffic levels, growth, or changes to the cable plant

and other hardware—might still require changing the subnets and IP addresses assigned to a particular

cable modem.

Note The ip address negotiated command cannot be used on the cable interface because this

command is reserved exclusively for the serial interface. However, in Cisco IOS

Release 12.1(3a)T1 when the ip address dhcp command is used for cable interfaces, the

configuration files still show the ip address negotiated command, which can generate an

“invalid input” error during boot. This is only a cosmetic issue and does not affect the

unit’s functionality. See the description of caveat CSCdr61697, page 33, for more

information.