Bridging Operations - Cisco uBR905 Installation Manual

Overview of the Cisco uBR905 Cable Access Router
In this mode, the router operates as an IP bridge between its cable and Ethernet interfaces, performing
the following functions:
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In addition to providing DOCSIS connectivity, the Cisco uBR905 router can also function as an IP
router, using static routes and the RIPv2 routing protocol. When operating in routing mode, the
Cisco uBR905 router can optionally provide advanced data and routing features, such as IPsec
encryption.
In both bridging and routing modes, the router can connect one or more computers to the Internet over
the HFC cable system. Subscribers can use the Cisco uBR905 router to create high-speed, permanent
access to the Internet, without the need for telco-based services such as leased lines.
Based on the feature licenses your company purchased, other Cisco IOS images can be downloaded
from Cisco Connection Online (CCO). These images provide additional functionality such as advanced
routing capabilities, firewall protection, and high-security encryption.
For most residential applications that involve basic Internet access, the Cisco uBR905 router is
configured as a bridge. For residential and SOHO applications that involve special feature sets such as
the firewall feature set, or that include connection to an existing network at the site, the Cisco uBR905
is configured as a router.
Bridging and routing operations are summarized in the following sections.

Bridging Operations

When acting as a DOCSIS-compliant cable modem, the Cisco uBR905 router provides DOCSIS IP
bridging for one or more PCs and other customer premises equipment (CPE). The router ships from the
factory with a Cisco IOS software image stored in nonvolatile Flash memory that supports
DOCSIS-compliant bridging data operations.
When installed and configured as a bridge, the Ethernet hub ports at the rear of the Cisco uBR905 router
can be connected directly to PCs at the subscriber site. A maximum of four PCs can be directly
connected to the router's hub ports, or a maximum of 254 PCs can be connected if one of the four
Ethernet hub ports is connected to a standard 10BaseT Ethernet hub, which then connects to additional
computers (or hubs) at the site.
Regardless of the configuration, Cisco IOS software treats all four Ethernet hub ports as one Ethernet
interface. See Figure 1-1 for a typical configuration.
Cisco uBR905 Router Hardware Installation Guide
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Traffic from the cable interface is sent to the Ethernet ports for transmission to the connected CPE
devices.
Traffic from the Ethernet ports is sent to the cable interface for transmission to the Internet (or other
network) by the gateway at the headend.
Chapter 1 Product Overview
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