Cisco Systems UBR900 specifications Routing Applications

Feature Overview

The Cisco uBR900 series complies with the DOCSIS standards for interoperable cable access routers; it supports full transparent bridging as well as DOCSIS-compliant transparent bridging.

Note If the attached CPE devices and the coaxial cable interface are in different IP subnets, the cable interface must have a secondary address.

Figure 2 Cisco uBR900 Series Cable Access Router in a Bridging Configuration

	CATV
	coaxial cable
Cisco uBR7200 series	Cisco uBR900 series
CMTS
	cable access router
HFC network

Ethernet

Ethernet

Ethernet

Ethernet

PC

PC

PC

PC or hub

13305

DOCSIS-compliant transparent bridging is the factory default configuration of the Cisco uBR900 series cable access router. If your cable service provider is using a DHCP server, all you need to do is connect the cables and power on the cable access router; 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 DOCSIS-compliant bridging mode, the cable access router is able to locate a downstream and upstream channel; find the TOD, TFTP, and DHCP server(s); obtain an IP address; download a DOCSIS configuration file; and obtain DHCP parameters to work in a bridging mode.

You can configure a customized bridging application on the Cisco uBR900 series using a downloadable configuration file or the CLI. See the sections “Configuring Bridging” on page 41 and “Customizing the Cable Access Router Interface” on page 44 for details.

Routing Applications

The Cisco uBR900 series cable access router can be configured to act as a router to preserve IP address space and limit broadcasts that can impact the performance of the network. A typical use would be if you are connecting the cable access router to an internal Ethernet hub that is connected to an existing PC network. The Cisco uBR900 series supports Routing Information Protocol Version 2 (RIP V2) for this application.

When configured in routing mode, the Cisco uBR900 series is automatically configured to use the headend’s IP address as its IP default gateway. This allows the cable access router to send packets not intended for the Ethernet interface to the headend when IP host-routing is configured.

RIP V2 routing is useful for small internetworks in that it enables optimization of Network Interface Center (NIC)-assigned IP addresses by defining variable-length subnet masks (VLSMs) for network addresses, and it allows classless interdomain routing (CIDR) addressing schema.

8Cisco IOS Release 12.0(7)T