![]() ![]() Scopes are the IP address ranges which are to be assigned to a network. Policies are a list of DHCP options that get associated with a scope. ![]() In the CMTS configuration section, the uBR7100 is configured to register cable modems, and forward cable modem traffic to the rest of the LAN.Ĭonfiguring CNR consist of configuring policies and scopes for the cable modems and hosts. CNR is used to assign IP address via DHCP and give the modems the network connectivity information they need to access key elements of the network. This document uses the configurations shown below.Ĭonfiguration is broken into two parts: CNR server configuration, and the CMTS configuration. Note: To find additional information on the commands used in this document, use the Command Lookup Tool ( registered customers only). Subsequently, the modem will get ToD (from either an external server within the bridge group or the CMTS configured to be the ToD server) and its configuration file via Trivial File Transfer Protocol (TFTP), and register with the CMTS. Since the CNR server is in the same bridge group it will hear the DHCP discover, and will respond with a DHCP offer. When a cable modem broadcasts a DHCP discover the cable interface on the CMTS will forward it to the other interfaces in the bridge group. This is convenient, since we can put the CNR server, the CMTS and the cable modems on the same network. This means that every device associated with one of these interfaces will hear broadcasts from all devices in the bridge group. All interfaces associated with the bridge group are considered a part of the broadcast domain. In bridge mode all of the interfaces on the CMTS are configured in one bridge group. If BPI is enabled, the modem will exchange encryption keys with the CMTS before being fully registered. If Baseline Privacy (BPI) is not enabled, the modem will register with the CMTS. Once the modem is configured it will send a registration request to the CMTS. Once the modem has IP connectivity it can request Time of Day (ToD) and download its cable modem configuration file. The modem and the CNR server will exchange a series of messages that result in the modem having IP connectivity to the rest of the network. The CNR server should hear the modems discover. Once the cable modem and the CMTS agree on the appropriate transmit level the modem will initiate the Dynamic Host Configuration Protocol (DHCP) process. The UCD has forward error correction (FEC) parameters, upstream frequency, modulation type, and symbol rate. The Upstream Channel Descriptor (UCD), which the cable modem reads from the downstream carrier, tells the modem how to transmit. The modem will lock on to the first DOCSIS carrier it detects. When the cable is plugged in for the first time it will scan the downstream for a DOCSIS carrier. Background Theoryįrom the customer prospective DOCSIS is "plug and play," meaning that the cable modem is automatically configured from the network. If you are working in a live network, ensure that you understand the potential impact of any command before using it. All of the devices used in this document started with a cleared (default) configuration. The information presented in this document was created from devices in a specific lab environment. This configuration was developed and tested using the following:Ĭisco uBR7100 Series Universal Broadband Routers running Cisco IOS version 12.10EC1Ĭisco Network Registrar (CNR) running V 5.5 The reader should have a basic understanding of the DOCSIS protocol and the Cisco IOS® command line on the uBR series routers. Before You Begin Conventionsįor more information on document conventions, see the Cisco Technical Tips Conventions. CNR can reside behind the gateway/router, in which case the gateway is configured with an IP helper address to route broadcasts between the cable modems and the CNR. The bridging configuration puts the Cisco Network Registrar (CNR) server on the same network as the CMTS and the cable modems. Since the routing functions are not done on the uBR7100 the configuration is streamlined. In this configuration, routing functions are done on the uBR7100's gateway/router. The bridging configuration consists of disabling IP routing, putting all of the interfaces in one bridge group, and configuring the cable interface. Unlike the uBR7200, the uBR7100 can be used as a bridge. This document details the configuration of the uBR7100 and Cisco Network Registrar for bridged network. ![]()
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