Cisco Network Registrar

Document ID: 13546

Contents

Introduction
Prerequisites
      Requirements
      Components Used
Configuration
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Introduction

Having discontiguous network address spaces can cause some complexities for cable networks. This document offers a solution to the challenge of running a network with these multiple network addresses.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

This document is not restricted to specific software and hardware versions.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Configuration

Assume in this setup, the cable modems (CMs) use these addresses:

10.0.1.0
10.0.2.0
30.0.1.0
30.0.2.0

The customer premises equipment (CPE's) use the following network addresses at their homes:

213.47.224.0
213.47.225.0
201.10.10.0
201.10.11.0

Note: You will notice a mixture of contiguous and discontiguous network address for demonstration purposes.

Configure the Cable Modem Terminal Server (CMTS).

int cable x/y
ip address 10.0.1.1 255.255.255.0  

!--- This is the PRIMARY address on the CMTS - note it is a 24 bit SN mask.

ip address 213.47.224.1 255.255.255.0 secondary 

!--- Make sure that this is the FIRST secondary address you enter on the cable interface, 
!--- this will be the primary scope for the CPEs.
 
ip address 10.0.2.1 255.255.255.0 secondary
ip address 30.0.1.1 255.255.255.0 secondary
ip address 30.0.2.1 255.255.255.0 secondary
ip address 213.47.225.1 255.255.255.0 secondary
ip address 201.10.10.1 255.255.255.0 secondary
ip address 201.10.11.1 255.255.255.0 secondary

Thus:

This is all that is needed in the router configuration, so in this setup you would not need any setrouter.tcl or relay.tcl scripts.

Now on the Cisco Network Registrar (CNR) system, you would create a primary scope for the CM's containing the addresses 10.0.1.2 - 10.0.1.254, and linked to the policy policy1. This policy1 has the "routers" field set to 10.0.1.1.

Note: By default, a scope is a primary scope when created.

Then you configure scopes for 10.0.2.0, 30.0.1.0 and 30.0.2.0, and mark these scopes as secondary to the 10.0.1.0 scope. Making a scope secondary of an existing scope can be done in different ways:

• Through the nrcmd interface (all CNR versions):

  nrcmd> scope scope_name set primary-scope primary_scope_name
  
  nrcmd> dhcp reload
  

• Through the Win32 GUI (CNR version 5.5 and eariler):

  1. Expand the DHCP server in the Server Manager, so that you will see all the scopes defined.

  2. Highlight the scope you want configure as secondary, and click Show Properties.

  3. Select the Advanced tab.

  4. Activate the Make this scope a secondary checkbox, and specify the name or IP network of the primary scope.

  5. Reload the DHCP server.

• Through the CNR WebUI (CNR version 6.0 and later):

  1. Go to DHCP > Scopes.

  2. Open the scope you want to make secondary by opening the hyperlink.

  3. Look for the Primary Subnet attribute, and set it to the primary network for the scope.

  4. Scroll down to the bottom of the page and click Modify Scope.

  5. Do not forget to reload the DHCP server for the change to take effect.

Link policy2 to 10.0.2.0 scope, and "routers" will be 10.0.2.1 in policy2. Link policy3 to 30.0.1.0 scope, and "routers" will be 30.0.1.1 in policy3 and so on.

Do the same for the CPE addresses. Create a primary scope with the 213.47.224.0 addresses, and make all the other CPE address scopes secondary to this primary. Then link an individual policy to each subnet, with the "routers" option set accordingly.

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