Cisco uBR7200 Series Software Configuration Guide - Chapter 7: Overview of the Cisco Network Registrar for the Cisco uBR7200 Series [Cisco uBR7200 Series Universal Broadband Routers]

Table Of Contents

Overview of the Cisco Network Registrar for the Cisco uBR7200 Series

Cisco Network Registrar Description

Cable Modem DHCP Response Fields

DOCSIS DHCP Fields

DHCP Relay Option (DOCSIS Option 82)

Overview of Scripts

Two-way Cable Modem Scripts

Telco Return Cable Modem Scripts

Placement of Scripts

Windows NT

Solaris

Activate Scripts in Cisco Network Registrar

Configuring the Cisco uBR7200 Series to Use Scripts

Configure the System Default Policy

Cable Modems

PCs

Create Selection Tag Scopes

General

Telco Return

Create Network Scopes

Create Policies for Class of Service or for Upgrading Cable Modem Cisco IOS Images

CNR Steps to Support Subinterfaces

Overview of the Cisco Network Registrar for the Cisco uBR7200 Series

This chapter supplements the Cisco Network Registrar (CNR) documentation by providing additional cable-specific instructions that are pertinent to the Cisco uBR7200 series and CMTS management.

For additional information about CNR, refer to these documents on Cisco.com:

•Cisco Network Registrar for the Cisco uBR7200 Series Universal Broadband Routers

•CNR and DHCP FAQs for Cable Environment

•Recommended CNR Settings and Management

Cisco Network Registrar Description

CNR is a dynamic IP address management system, currently running on Windows NT or Solaris 2.6, that uses the Dynamic Host Configuration Protocol (DHCP) to assign IP addresses to cable interfaces, PCs, and other devices on the broadband network. The CNR tool includes script extensions that allow a cable system administrator to define and view individual DHCP options, define the identity or type of device on the network, and assign the device to a predefined class or group.

Using the CNR tool, a cable system administrator can specify policies to provide:

•Integrated DHCP and Domain Name Server (DNS) services

•Time of Day (ToD) and Trivial File Transfer Protocol (TFTP) server based on the size of the network

•DHCP safe failover and dynamic DNS updates

Note This is available only in CNR 3.0 or higher.

Using the CNR tool and the extension scripts identified in the "Overview of Scripts" section, a cable system administrator can specify scopes, policies, and options for the network and each cable interface based on the services and configuration to support at each subscriber site.

Note Scopes refer to the administrative grouping of TCP/IP addresses; all IP addresses within a scope should be on the same subnet.

The cable system administrator defines system default policies for all standard options and uses scope-specific policies for options related to particular subnets, such as cable interfaces. This allows DHCP to send the information with the IP address.

Seven entry points exist for scripts:

•post-packet-decode

•pre-client-lookup

•post-client-lookup—Examines and takes action on results of the client-class process, places data items in the environment dictionary to use at the pre-packet-encode extension point, includes DHCP relay option

•check-lease-acceptable

•pre-packet-encode

•post-sent-packet

•pre-dns-add-forward

Cable Modem DHCP Response Fields

Each cable interface on the broadband network requires the following fields in the DHCP response:

•CM's IP address

•CM's subnet mask

Note For cable operators with less experience in networking, you can fill in a guess based on the network number and indicate how your IP network is divided.

•Name of the DOCSIS configuration file on the TFTP server intended for the cable interface

•Time offset of the cable interface from the Universal Coordinated Time (UTC), which the cable interface uses to calculate the local time when time-stamping error logs

•Time server address from which the cable interface obtains the current time

DOCSIS DHCP Fields

DOCSIS DHCP option requirements include:

•IP address of the next server to use in the TFTP bootstrap process; this is returned in the siaddr field

•DOCSIS configuration file that the cable interface downloads from the TFTP server

Note If the DHCP server is on a different network that uses a relay agent, then the relay agent must set the gateway address field of the DHCP response.

•IP address of the security server should be set if security is required

DHCP Relay Option (DOCSIS Option 82)

DOCSIS Option82 modifies DHCPDISCOVER packets to distinguish cable interfaces from the CPE devices or "clients" behind them. The DOCSIS Option82 is comprised of the following two suboptions:

•Suboption 1, Circuit ID:
Type 1 (1 byte)
Len 4 (1 byte)
Value (8 bytes)
<bit 31,30,....................0)
<xYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY> 
where the MSB indicates if the attached device is a cable interface.

x=1 Cable Modem REQ

x=0 CPE device
(Behind the cable interface with the cable interface MAC address shown in suboption 2.)

The rest of the bits make up the SNMP index to the CMTS interface.

Y=0xYYYYYYY is the SNMP index to the CMTS interface.

•Suboption 2, MAC address of the cable interface:
Type 2 (1 byte)
Len 6 (1 byte)
Value xxxx.xxxx.xxxx (6 bytes)
For additional information about

Overview of Scripts

This section lists the scripts applicable to cable interface configuration.

Two-way Cable Modem Scripts

To support two-way configurations at a subscriber site, use these scripts:

•Relay.tcl

•SetRouter.tcl

Telco Return Cable Modem Scripts

To support telco return and two-way cable interface configurations on the same cable interface card or chassis, use these scripts:

•PostClientLookup.tcl

•PrePacketEncode.tcl

Placement of Scripts

Windows NT

For CNR running on Windows NT, place the appropriate scripts in the following directory:
\program files\network registrar\extensions\dhcp\scripts\tcl
Solaris

For CNR running on Solaris, place the appropriate scripts in the following directory:
/opt/nwreg2/extensions/dhcp/scripts/tcl
Activate Scripts in Cisco Network Registrar

To activate the scripts after you have placed them in the appropriate directory:

Step 1 Open up a text editor.

Step 2 Open one of the scripts at the nrcmd> command prompt.

Step 3 Create the extension points and attach them to the system.

Note The easiest way to do this is to simply cut and paste the command lines from the scripts to the nrcmd> command line.

Step 4 After you have created and attached the extension points, do a dhcp reload.

The scripts are active.

Configuring the Cisco uBR7200 Series to Use Scripts

Each cable interface must be set up as a BOOTP forwarder and have the relay-option enabled. The primary and secondary IP addresses for each cable interface must be in sync with the CNR tool.

To properly communicate with scripts in the system, implement the following commands on the Cisco uBR7200 series universal broadband router:

•On Cisco IOS Release 11.3—Command is interface specific:
cable relay-agent-option
This enables Option82 on the Cisco uBR7200 series.

•On Cisco IOS Release 12.0—Command has been changed to the following global option:
ip dhcp relay info option
•On Cisco IOS Release 12.0 to 12.5, use the following command:
no ip dhcp relay information option check
Note You can also use the cable dhcp-giaddr command in cable interface configuration mode to modify the GIADDR field of DHCPDISCOVER and DHCPREQUEST packets to provide a relay IP address before packets are forwarded to the DHCP server. Use this command to set a "policy" option such that primary addresses are used for CMs and secondary addresses are used for hosts behind the CMs.

Configure the System Default Policy

Add these options to the system default policy for:

•Cable modems to support on your network

•PCs to support behind each cable interface on your network

Cable Modems

Define these settings following the CNR tool documentation:

•TFTP server (IP address) for those cable interfaces using BOOTP

•Time-server (IP address)

•Time-offset (Hex value, 1440 for Eastern Standard Time)

•Packet-siaddr (IP address of CNR)

•Router (set to 0.0.0.0)

•Boot-file (name of .cm file for those cable interfaces using BOOTP)

•Packet-file-name (.cm file name)

PCs

Define these settings following the CNR tool documentation:

•Domain name

•Name servers (IP address of DNS servers)

Create Selection Tag Scopes

General

When you create your scope selection tags:

Step 1 Cut and paste the scope selection tag create commands from the scripts into the nrcmd> command line.

Note These names have to be exactly as they appear in the scripts.

Step 2 Then attach the selection tags to the appropriate scripts:

Example:

CM_Scope tagCablemodem

PC_Scope tagComputer

Telco Return

Note If you are using the prepacketencode and postclientlookup .tcl scripts for telco return, the telco return scope does not have a selection tag associated to the scope.

Step 1 Put the tag Telcocablemodem on the primary cable interface scope to pull addresses from that pool instead.

Step 2 Follow the same procedure as above, but use a telco return policy which has a different .cm file with telco-specific commands in it.

Create Network Scopes

Following is an example for creating scopes for your network. This example assumes two Cisco uBR7200 series universal broadband routers in two locations, with one cable interface card on one Cisco uBR7200 series configured for telco return.
cm-toledo1_2-0 10.2.0.0 255.255.0.0 assignable 10.2.0.10-10.2.254.254 tagCablemodem 
tagTelcomodem Default GW=10.2.0.1 (assigned by scripts)
cm-toledo1_3-0 10.3.0.0 255.255.0.0 assignable 10.3.0.10-10.3.254.254 tagCablemodem 
tagTelcomodem Default GW=10.3.0.1 (assigned by scripts)
pc-toledo1_2-0 208.16.182.0 255.255.255.248 assignable 208.16.182.2-208.16.182.6 
tagComputer Default GW=208.16.182.1 (assigned by scripts)
pc-toledo1_3-0 208.16.182.8 255.255.255.248 assignable 208.16.182.10-208.16.182.14 
tagComputer Default GW=208.16.182.9 (assigned by scripts)
telco_return_2-0 192.168.1.0 255.255.255.0 (No assignable addresses, tag was put on cable 
modem primary scope to force telco-return cable modem to pull address from primary scope)
cm-arlington1_2-0 10.4.0.0 255.255.0.0 assignable 10.4.0.10-10.4.254.254 tagCablemodem 
Default GW=10.4.0.1 (assigned by scripts)
cm-arlington1_3-0 10.5.0.0 255.255.0.0 assignable 10.5.0.10-10.5.254.254 tagCablemodem 
Default GW=10.5.0.1 (assigned by scripts)
pc-arlington1_2-0 208.16.182.16 255.255.255.248 assignable 208.16.182.17-208.16.182.22 
tagComputer Default GW=208.16.182.17 (assigned by scripts)
pc-toledo1_3-0 208.16.182.24 255.255.255.248 assignable 208.16.182.2-208.16.182.30 
tagComputer Default GW=208.16.182.25 (assigned by scripts)
Note Remember the last valid address in the .248 subnet range is the broadcast address; do not use this.

Create Policies for Class of Service or for Upgrading Cable Modem Cisco IOS Images

To support Class of Service (CoS), define:

•Scope selection tags—Identifiers that describe types of scope configurations

Note This is needed for Option82.

•Client classes—Class with which a group of clients is associated

Note Scope selection tags are excluded from or included in client-classes.

•Client—Specific DHCP clients and the defined class to which they belong

To assign the CoS or use Option82, make a client entry with a MAC address and point to the appropriate policy. To use client-based MAC provisioning, add a client entry "default - exclude," then put in MAC addresses for all devices (for example, cable interfaces and PCs) in the client tab and select the policy to use, including the appropriate tag.

Note For more detailed information about Cisco Network Registrar, please refer to the document Cisco Network Registrar for the Cisco uBR10000 Series Universal Broadband Routers.

CNR Steps to Support Subinterfaces

The CNR configuration is done differently if subinterfaces are configured. Here is an example. If you have configured two ISP subinterfaces and one management subinterface on a Cisco uBR7200 series, make sure that the management subinterface is the first subinterface that is configured. If cable interface three—c3/0—is being used, create c3/0.1, c3/0.2 and c3/0.3 as three subinterfaces and c3/0.1 as the first subinterface configured as the management subinterface.

Note The Cisco uBR7200 series requires management subinterfaces to route DHCP packets from CMs when they first initialize because the Cisco uBR7200 series does not know the subinterfaces they belong to until it has seen the IP addresses assigned to them by gleaning DHCP reply message from CNR.

In CNR, complete the following steps for such a configuration:

Step 1 Create two scope selection tags such as: isp1-cm-tag and isp2-cm-tag

Step 2 Configure three scopes; for example, mgmt-scope, isp1-cm-scope, and isp2-cm-scope such that isp1-cm-scope and isp2-cm-scope each define mgmt-scope to be the primary scope

Step 3 Also configure two scopes for PCs for each of the ISPs; isp1-pc-scope and isp2-pc-scope. For scope isp1-cm-scope, configure isp1-cm-tag to be the scope selection tag. For scope isp2-cm-scope, configure isp2-cm-tag to be the scope selection tag

Step 4 Configure two client classes; for example, isp1-client-class and isp2-client-class

Step 5 Create client entries with their MAC addresses for CMs that belong to ISP1 and assign them to isp1-client-class. Also assign the scope selection tag isp1-cm-tag

Step 6 Create client entries for CMs that belong to ISP2 and assign them to isp2-client-class. Also assign the scope selection tag isp2-cm-tag

Step 7 Enable client class processing from the scope-selection-tag window

Note Overlapping address ranges cannot be configured on these subinterfaces because software gleans the DHCP reply to figure out the subinterface it really belongs to. Although CNR can be configured with overlapping address range scopes, it cannot be used to allocate addresses from these scopes.

	Cisco uBR7200 Series Software Configuration Guide
	Chapter 7: Overview of the Cisco Network Registrar for the Cisco uBR7200 Series
Cisco uBR7200 Series Software Configuration Guide Preface Chapter 1: Overview of Cisco uBR7200 Series Software Chapter 2: Configuring the Cable Modem Termination System for the First Time Chapter 3: Configuring Cable Modem Interface Features Chapter 4: Configuring DOCSIS Baseline Privacy Interface on the Cisco uBR7200 Series Chapter 5: Managing Cable Modems on the Hybrid Fiber-Coaxial Network Chapter 6: Configuring Basic Broadband Internet Access Chapter 7: Overview of the Cisco Network Registrar for the Cisco uBR7200 Series Chapter 8: Troubleshooting the System Appendix A: Installing or Upgrading Cisco IOS Software Appendix B: Resolving Common Image Installation Problems Appendix C: Viewing Sample Configuration Files Appendix D: Frequency Allocation Tables Appendix E: Configuration Register Information for the Cisco uBR7200 Series Universal Broadband Routers	Download this chapter Chapter 7: Overview of the Cisco Network Registrar for the Cisco uBR7200 Series Download the complete book Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide (PDF - 8 MB) Feedback Table Of Contents Overview of the Cisco Network Registrar for the Cisco uBR7200 Series Cisco Network Registrar Description Cable Modem DHCP Response Fields DOCSIS DHCP Fields DHCP Relay Option (DOCSIS Option 82) Overview of Scripts Two-way Cable Modem Scripts Telco Return Cable Modem Scripts Placement of Scripts Windows NT Solaris Activate Scripts in Cisco Network Registrar Configuring the Cisco uBR7200 Series to Use Scripts Configure the System Default Policy Cable Modems PCs Create Selection Tag Scopes General Telco Return Create Network Scopes Create Policies for Class of Service or for Upgrading Cable Modem Cisco IOS Images CNR Steps to Support Subinterfaces Overview of the Cisco Network Registrar for the Cisco uBR7200 Series This chapter supplements the Cisco Network Registrar (CNR) documentation by providing additional cable-specific instructions that are pertinent to the Cisco uBR7200 series and CMTS management. For additional information about CNR, refer to these documents on Cisco.com: •Cisco Network Registrar for the Cisco uBR7200 Series Universal Broadband Routers •CNR and DHCP FAQs for Cable Environment •Recommended CNR Settings and Management Cisco Network Registrar Description CNR is a dynamic IP address management system, currently running on Windows NT or Solaris 2.6, that uses the Dynamic Host Configuration Protocol (DHCP) to assign IP addresses to cable interfaces, PCs, and other devices on the broadband network. The CNR tool includes script extensions that allow a cable system administrator to define and view individual DHCP options, define the identity or type of device on the network, and assign the device to a predefined class or group. Using the CNR tool, a cable system administrator can specify policies to provide: •Integrated DHCP and Domain Name Server (DNS) services •Time of Day (ToD) and Trivial File Transfer Protocol (TFTP) server based on the size of the network •DHCP safe failover and dynamic DNS updates Note This is available only in CNR 3.0 or higher. Using the CNR tool and the extension scripts identified in the "Overview of Scripts" section, a cable system administrator can specify scopes, policies, and options for the network and each cable interface based on the services and configuration to support at each subscriber site. Note Scopes refer to the administrative grouping of TCP/IP addresses; all IP addresses within a scope should be on the same subnet. The cable system administrator defines system default policies for all standard options and uses scope-specific policies for options related to particular subnets, such as cable interfaces. This allows DHCP to send the information with the IP address. Seven entry points exist for scripts: •post-packet-decode •pre-client-lookup •post-client-lookup—Examines and takes action on results of the client-class process, places data items in the environment dictionary to use at the pre-packet-encode extension point, includes DHCP relay option •check-lease-acceptable •pre-packet-encode •post-sent-packet •pre-dns-add-forward Cable Modem DHCP Response Fields Each cable interface on the broadband network requires the following fields in the DHCP response: •CM's IP address •CM's subnet mask Note For cable operators with less experience in networking, you can fill in a guess based on the network number and indicate how your IP network is divided. •Name of the DOCSIS configuration file on the TFTP server intended for the cable interface •Time offset of the cable interface from the Universal Coordinated Time (UTC), which the cable interface uses to calculate the local time when time-stamping error logs •Time server address from which the cable interface obtains the current time DOCSIS DHCP Fields DOCSIS DHCP option requirements include: •IP address of the next server to use in the TFTP bootstrap process; this is returned in the siaddr field •DOCSIS configuration file that the cable interface downloads from the TFTP server Note If the DHCP server is on a different network that uses a relay agent, then the relay agent must set the gateway address field of the DHCP response. •IP address of the security server should be set if security is required DHCP Relay Option (DOCSIS Option 82) DOCSIS Option82 modifies DHCPDISCOVER packets to distinguish cable interfaces from the CPE devices or "clients" behind them. The DOCSIS Option82 is comprised of the following two suboptions: •Suboption 1, Circuit ID: Type 1 (1 byte) Len 4 (1 byte) Value (8 bytes) <bit 31,30,....................0) <xYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY> where the MSB indicates if the attached device is a cable interface. x=1 Cable Modem REQ x=0 CPE device (Behind the cable interface with the cable interface MAC address shown in suboption 2.) The rest of the bits make up the SNMP index to the CMTS interface. Y=0xYYYYYYY is the SNMP index to the CMTS interface. •Suboption 2, MAC address of the cable interface: Type 2 (1 byte) Len 6 (1 byte) Value xxxx.xxxx.xxxx (6 bytes) For additional information about Overview of Scripts This section lists the scripts applicable to cable interface configuration. Two-way Cable Modem Scripts To support two-way configurations at a subscriber site, use these scripts: •Relay.tcl •SetRouter.tcl Telco Return Cable Modem Scripts To support telco return and two-way cable interface configurations on the same cable interface card or chassis, use these scripts: •PostClientLookup.tcl •PrePacketEncode.tcl Placement of Scripts Windows NT For CNR running on Windows NT, place the appropriate scripts in the following directory: \program files\network registrar\extensions\dhcp\scripts\tcl Solaris For CNR running on Solaris, place the appropriate scripts in the following directory: /opt/nwreg2/extensions/dhcp/scripts/tcl Activate Scripts in Cisco Network Registrar To activate the scripts after you have placed them in the appropriate directory: Step 1 Open up a text editor. Step 2 Open one of the scripts at the nrcmd> command prompt. Step 3 Create the extension points and attach them to the system. Note The easiest way to do this is to simply cut and paste the command lines from the scripts to the nrcmd> command line. Step 4 After you have created and attached the extension points, do a dhcp reload. The scripts are active. Configuring the Cisco uBR7200 Series to Use Scripts Each cable interface must be set up as a BOOTP forwarder and have the relay-option enabled. The primary and secondary IP addresses for each cable interface must be in sync with the CNR tool. To properly communicate with scripts in the system, implement the following commands on the Cisco uBR7200 series universal broadband router: •On Cisco IOS Release 11.3—Command is interface specific: cable relay-agent-option This enables Option82 on the Cisco uBR7200 series. •On Cisco IOS Release 12.0—Command has been changed to the following global option: ip dhcp relay info option •On Cisco IOS Release 12.0 to 12.5, use the following command: no ip dhcp relay information option check Note You can also use the cable dhcp-giaddr command in cable interface configuration mode to modify the GIADDR field of DHCPDISCOVER and DHCPREQUEST packets to provide a relay IP address before packets are forwarded to the DHCP server. Use this command to set a "policy" option such that primary addresses are used for CMs and secondary addresses are used for hosts behind the CMs. Configure the System Default Policy Add these options to the system default policy for: •Cable modems to support on your network •PCs to support behind each cable interface on your network Cable Modems Define these settings following the CNR tool documentation: •TFTP server (IP address) for those cable interfaces using BOOTP •Time-server (IP address) •Time-offset (Hex value, 1440 for Eastern Standard Time) •Packet-siaddr (IP address of CNR) •Router (set to 0.0.0.0) •Boot-file (name of .cm file for those cable interfaces using BOOTP) •Packet-file-name (.cm file name) PCs Define these settings following the CNR tool documentation: •Domain name •Name servers (IP address of DNS servers) Create Selection Tag Scopes General When you create your scope selection tags: Step 1 Cut and paste the scope selection tag create commands from the scripts into the nrcmd> command line. Note These names have to be exactly as they appear in the scripts. Step 2 Then attach the selection tags to the appropriate scripts: Example: CM_Scope tagCablemodem PC_Scope tagComputer Telco Return Note If you are using the prepacketencode and postclientlookup .tcl scripts for telco return, the telco return scope does not have a selection tag associated to the scope. Step 1 Put the tag Telcocablemodem on the primary cable interface scope to pull addresses from that pool instead. Step 2 Follow the same procedure as above, but use a telco return policy which has a different .cm file with telco-specific commands in it. Create Network Scopes Following is an example for creating scopes for your network. This example assumes two Cisco uBR7200 series universal broadband routers in two locations, with one cable interface card on one Cisco uBR7200 series configured for telco return. cm-toledo1_2-0 10.2.0.0 255.255.0.0 assignable 10.2.0.10-10.2.254.254 tagCablemodem tagTelcomodem Default GW=10.2.0.1 (assigned by scripts) cm-toledo1_3-0 10.3.0.0 255.255.0.0 assignable 10.3.0.10-10.3.254.254 tagCablemodem tagTelcomodem Default GW=10.3.0.1 (assigned by scripts) pc-toledo1_2-0 208.16.182.0 255.255.255.248 assignable 208.16.182.2-208.16.182.6 tagComputer Default GW=208.16.182.1 (assigned by scripts) pc-toledo1_3-0 208.16.182.8 255.255.255.248 assignable 208.16.182.10-208.16.182.14 tagComputer Default GW=208.16.182.9 (assigned by scripts) telco_return_2-0 192.168.1.0 255.255.255.0 (No assignable addresses, tag was put on cable modem primary scope to force telco-return cable modem to pull address from primary scope) cm-arlington1_2-0 10.4.0.0 255.255.0.0 assignable 10.4.0.10-10.4.254.254 tagCablemodem Default GW=10.4.0.1 (assigned by scripts) cm-arlington1_3-0 10.5.0.0 255.255.0.0 assignable 10.5.0.10-10.5.254.254 tagCablemodem Default GW=10.5.0.1 (assigned by scripts) pc-arlington1_2-0 208.16.182.16 255.255.255.248 assignable 208.16.182.17-208.16.182.22 tagComputer Default GW=208.16.182.17 (assigned by scripts) pc-toledo1_3-0 208.16.182.24 255.255.255.248 assignable 208.16.182.2-208.16.182.30 tagComputer Default GW=208.16.182.25 (assigned by scripts) Note Remember the last valid address in the .248 subnet range is the broadcast address; do not use this. Create Policies for Class of Service or for Upgrading Cable Modem Cisco IOS Images To support Class of Service (CoS), define: •Scope selection tags—Identifiers that describe types of scope configurations Note This is needed for Option82. •Client classes—Class with which a group of clients is associated Note Scope selection tags are excluded from or included in client-classes. •Client—Specific DHCP clients and the defined class to which they belong To assign the CoS or use Option82, make a client entry with a MAC address and point to the appropriate policy. To use client-based MAC provisioning, add a client entry "default - exclude," then put in MAC addresses for all devices (for example, cable interfaces and PCs) in the client tab and select the policy to use, including the appropriate tag. Note For more detailed information about Cisco Network Registrar, please refer to the document Cisco Network Registrar for the Cisco uBR10000 Series Universal Broadband Routers. CNR Steps to Support Subinterfaces The CNR configuration is done differently if subinterfaces are configured. Here is an example. If you have configured two ISP subinterfaces and one management subinterface on a Cisco uBR7200 series, make sure that the management subinterface is the first subinterface that is configured. If cable interface three—c3/0—is being used, create c3/0.1, c3/0.2 and c3/0.3 as three subinterfaces and c3/0.1 as the first subinterface configured as the management subinterface. Note The Cisco uBR7200 series requires management subinterfaces to route DHCP packets from CMs when they first initialize because the Cisco uBR7200 series does not know the subinterfaces they belong to until it has seen the IP addresses assigned to them by gleaning DHCP reply message from CNR. In CNR, complete the following steps for such a configuration: Step 1 Create two scope selection tags such as: isp1-cm-tag and isp2-cm-tag Step 2 Configure three scopes; for example, mgmt-scope, isp1-cm-scope, and isp2-cm-scope such that isp1-cm-scope and isp2-cm-scope each define mgmt-scope to be the primary scope Step 3 Also configure two scopes for PCs for each of the ISPs; isp1-pc-scope and isp2-pc-scope. For scope isp1-cm-scope, configure isp1-cm-tag to be the scope selection tag. For scope isp2-cm-scope, configure isp2-cm-tag to be the scope selection tag Step 4 Configure two client classes; for example, isp1-client-class and isp2-client-class Step 5 Create client entries with their MAC addresses for CMs that belong to ISP1 and assign them to isp1-client-class. Also assign the scope selection tag isp1-cm-tag Step 6 Create client entries for CMs that belong to ISP2 and assign them to isp2-client-class. Also assign the scope selection tag isp2-cm-tag Step 7 Enable client class processing from the scope-selection-tag window Note Overlapping address ranges cannot be configured on these subinterfaces because software gleans the DHCP reply to figure out the subinterface it really belongs to. Although CNR can be configured with overlapping address range scopes, it cannot be used to allocate addresses from these scopes.
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