Specifications

Configuration Options

Bridging and Routing Features for the Cisco uBR904 Cable Modem 7

Conﬁguration Options

The Cisco uBR904 cable modem is usually conﬁgured automatically via a conﬁguration ﬁle

generated by the cable service provider; however, you can also manually conﬁgure the cable modem

to function either as a bridge or as a router. The following sections give brief descriptions of both

applications.

Note When the unit is shipped from the factory, it is conﬁgured for bridging by default.

Bridging

The Cisco uBR904 cable modem complies with the MCNS standards for interoperable cable

modems; it supports full transparent bridging as well as DOCSIS-compliant transparent bridging.

In bridging applications, the Cisco uBR904 acts as a transparent bridge for up to three PCs plugged

directly into three of the four Ethernet ports on the rear panel of the unit. The cable modem is

connected to the Internet via the coaxial cable. All three Ethernet ports are treated as one Ethernet

interface by the Cisco IOS software. The IP addresses for the PCs and the coaxial cable interface are

in the same subnet.

Figure 4 Cisco uBR904 in a Bridging Conﬁguration

DOCSIS-compliant transparent bridging is the default conﬁguration of the Cisco uBR904 cable

modem. If your cable service provider is using a DHCP server, all you need to do is connect the

cables and power on the cable modem; your service provider’s conﬁguration program will

automatically conﬁgure both the coaxial cable interface and the bridging functionality. You do not

need to set up IP addresses for the attached PCs or enter any Command Line Interface (CLI)

conﬁguration commands. This type of operation is called plug-and-play bridging.

In addition to the plug-and-play method, you can conﬁgure a bridging application on the

Cisco uBR904 using one of the following methods:

• Manual conﬁguration using the CLI. See the sections “Conﬁguring Bridging” on page 13 and

“Customizing the Cable Modem Interface” on page 16 for details.

• Advanced conﬁguration using the System Conﬁguration dialog box in the setup facility. See the

chapter “Conﬁguring Advanced Routing or Bridging Using Setup” in the Cisco uBR904 Cable

Modem Installation and Conﬁguration Guide for details.

Cisco uBR7200 series

CMTS

CATV

coaxial cable

HFC network

Cisco uBR900 series

cable access router

Ethernet

13305

Ethernet

PC or hub