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This document describes the Cisco Network Registrar (CNR) software product and how to install CNR and use it to provision a hybrid fiber coaxial (HFC) network that uses Cisco uBR7200 series universal broadband routers at the headend. This document contains the following sections:
Cisco Network Registrar (CNR) is a dynamic IP address management system that uses the Dynamic Host Configuration Protocol (DHCP) and assigns IP addresses to PCs and other devices on a network based on a predefined set of policies, such as class of service. CNR assigns available IP addresses from address pools based on the identity or type of the requesting device and the policies in effect. For example, CNR can distinguish between registered devices, unregistered devices, and registered devices that have been assigned to a particular class of service.
CNR also provides extensions that can be customized (via programming or a script) so that you can view individual DHCP options, determine the identity or type of a device based on the content of the options, and assign a device to a predefined class or group. Using these extensions, you can determine the difference between PCs and cable modems and assign them IP addresses from different address pools.
In typical data-over-cable environments, service providers are interested in simplifying provisioning to limit the amount of information that must be collected about subscribers' customer premise equipment (CPEs). To support current provisioning models, a field technician must be sent to a subscriber's home or business to install and setup a cable modem. During this site visit, the technician might register the serial number and MAC address of the cable modem in the customer account database. Because a field technician must go to a subscriber's site to replace a cable modem, you can easily track modem information.
Manually registering and tracking information about a cable subscriber's PC is more difficult. A subscriber might purchase a new PC or exchange the network interface card (NIC) without notifying you of the change. Automatic provisioning with CNR reduces the amount of customer service involvement needed to track customer equipment. To use the provisioning model described in this document, you must still track serial numbers and MAC addresses for cable modems, but you do not need to track information about the PC or NIC cards installed at a subscriber site.
The remainder of this document describes how to configure CNR to support this model. The following sections describe the equipment and servers required for the cable headend, provide an overview of the interaction between DOCSIS-compatible cable modems and the Cisco uBR7200 series universal broadband routers, and provide a guide on how to configure CNR to support this provisioning model.
A TFTP server, DHCP server, and time-of-day (TOD) server are required to support two-way data cable modems on an HFC network. A cable modem will not boot if these servers are not available. The log server and security servers are not required to configure and operate a cable modem. If the log server or security servers are not present, a cable modem will generate warning messages, but it will continue to boot and function properly. (See Figure 1.)
In this provisioning model, TOD and TFTP servers are standard Internet implementations of the RFC 868 and RFC 1350 specifications. Most computers running a UNIX-based operating system supply TOD and TFTP servers as a standard software feature. Typically, the TOD server is embedded in the UNIX inetd and it requires no additional configuration. The TFTP server is usually disabled in the standard software but can be enabled by the user. Microsoft NT server software includes a TFTP server that can be enabled with the services control panel. Microsoft NT does not include a TOD server. A public domain version of the TOD server for Microsoft NT can be downloaded from several sites. For more information, see the "Installing Cisco Network Registrar and Server Software" section.
The DHCP and Domain Name System (DNS) server shown in Figure 1 must be the DHCP/DNS server available in Cisco Network Registrar version 2.0 or later. CNR is the only DHCP server that implements policy-based assignment of IP addresses. The headend must be a Cisco uBR7200 series universal broadband router. The remote access server is only required on HFC networks that are limited to one-way (downstream only) communication. In a one-way HFC network, upstream data from a PC through the headend to the Internet is carried over a dialup connection. This dialup connection for upstream data is referred to as telco return. For simplification, the model will not include a log or security server. Cable modems can be set up to use the logging and security servers by including the appropriate DHCP options in the cable modem policy as described in the Cisco Network Registrar User Manual. (See the "For More Information" section.)
Cisco uBR7200 series routers and Cisco uBR904 cable modems are based on the Data Over Cable Service Interface Specification (DOCSIS) standards. These standards were created by a consortium of cable service providers called Multimedia Cable Network Systems, Ltd. (MCNS) to that cable headend and cable modem equipment produced by different vendors will interoperate. The key DOCSIS standards provide the basis for a cable modem to communicate with any headend equipment and headend equipment to communicate with any cable modem.
Cable modems are assigned to operate on specific cable channels so activity can be balanced across several channels. Each Cisco uBR7200 series router installed at the headend serves a specific channel. Part of network planning is to decide which channel each cable modem can use.
A cable modem cannot connect to the network until the following events occur:
DHCP options and packet fields are required to enable cable modems to boot and operate properly. Table 1 lists the required DHCP options and fields.
| Required Field/Option | Field/Option In Cisco Network Registrar | Value/Description |
|---|---|---|
| Fields |
|
|
giaddr | - | IP address. As a DHCP packet passes through the relay agent to the DHCP server, the relay agent supplies a unique IP address to the packet and stores it in this field. The relay agent is a uBR7200 series router with the iphelper attribute defined. |
subnet-mask | - | Subnet mask for the IP address stored in the giaddr field. This value is also stored in the DHCP packet by the relay agent. |
file | Packet-file-name | Name of the cable modem configuration file that will be read from a TFTP server. |
siaddr | Packet-siaddr | IP address of the TFTP server where configuration files are stored. |
| Options |
|
|
Time-servers | - | List of hosts running the time server specified in the RFC 868 standard. |
Time-offset | - | Time offset of a cable modem internal clock from Universal Time Coordinated (UTC). This value is used by cable modems to calculate the local time that is stored in time-stamping error logs. |
MCNS-security-server | - | IP address of the security server. This should be set if security is required. See RFC 1533 for details. |
If you order a Cisco uBR7200 series router with Cisco Network Registrar, you will receive a CD-ROM with the Cisco Network Registrar software. Install the software from this CD-ROM. If you order Cisco Network Registrar as a spare, you must download the software from CCO.
Cisco Network Registrar software for the Cisco uBR7200 series routers is available on CCO at:
For access to TOD server software, see the following web sites:
Yu can use the following information to set up Cisco Network Registrar in a trial configuration. The configuration describes DHCP-related setup only; it does not cover setting up DNS or configuring dynamic DNS (DDNS). You should be familiar with important CNR concepts including scopes, primary and secondary scopes, scope selection tags, client classes, and CNR policies. See the Using N etwork Registrar publication for detailed information on these concepts.
In the trial configuration, you can configure CNR to perform the following operations:
To perform these options, you must implement the following CNR configuration items:
Figure 2 shows the trial CNR configuration in an HFC network.
These configuration items and their associations can be created using either the CNR management graphical user interface (GUI) or command-line interface (CLI). The following sample script configures DHCP for a sample server:
File: cabledemo.rc Command line: nrcmd -C <cluster> -N <user name> -P <password> -b < cabledemo.rc --------------------------------------------------------------------------------------- scope-selection-tag tag-CM create scope-selection-tag tag-PC create client-class create class-CM client-class class-CM set selection-criteria=tag-CM client-class create class-PC client-class class-PC set selection-criteria=tag-PC policy cmts-cisco create policy cmts-cisco setleasetime 1800 policy cmts-cisco setoption domain-name-servers 192.168.10.2 policy cmts-cisco setoption routers 10.1.1.1 policy cmts-cisco setoption time-offset 604800 policy cmts-cisco setoption time-servers 192.168.10.20 policy cmts-cisco set packet-siaddr=192.168.10.2 policy cmts-cisco setoption log-servers 192.168.10.2 policy cmts-cisco setoption mcns-security-server 192.168.10.2 policy cmts-cisco set packet-file-name=golden.cfg policy cmts-cisco set dhcp-reply-options=packet-file-name,packet-siaddr,mcns-security-server policy pPC create policy pPC set server-lease-time 1800 policy pPC setleasetime 1800 policy pPC setoption domain-name-servers 192.168.10.2 policy pPC setoption routers 24.1.1.1 scope S24.1.1.0 create 24.1.1.0 255.255.255.0 scope S24.1.1.0 addrange 24.1.1.5 24.1.1.254 scope S24.1.1.0 set policy=pPC scope S24.1.1.0 set selection-tags=tag-PC scope S10.1.1.0 create 10.1.1.0 255.255.255.0 scope S10.1.1.0 addrange 10.1.1.5 10.1.1.254 scope S10.1.1.0 set policy=cmts-cisco scope S10.1.1.0 set selection-tags=tag-CM scope S10.1.1.0 set primary-scope=S24.1.1.0 client 01:02:03:04:05:06 create client-class-name=class-PC client ab:cd:ef:01:02:03 create client-class-name=class-CM client default create action=exclude dhcp enable client-class dhcp enable one-lease-per-client save dhcp reload
In addition to the DHCP server setup, you might want to enable packet-tracing. When packet-tracing is enabled, the server parses both requests and replies, and then adds them to the logs. If you do enable tracing, performance will be adversely affected, and the logs will roll over quickly.
Use the following nrcmd command to set packet tracing.
DHCP set log-settings=incoming-packet-detail,outgoing-packet-detail
For more information on Cisco Network Registrar, MCNS specifications, and DHCP specifications, see the following web sites and documents:
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