Maximum CPE and Host Parameters for the Cisco CMTS Routers

First Published: February 14, 2008

Last Updated: July 23, 2013


Note
Cisco IOS Release 12.2(33)SCA integrates support for this feature on the Cisco CMTS routers. This feature is also supported in Cisco IOS Release 12.3BC, and this document contains information that references many legacy documents related to Cisco IOS 12.3BC. In general, any references to Cisco IOS Release 12.3BC also apply to Cisco IOS Release 12.2SC.

This document describes how to use different methods to control subscriber access that are allowed by the Data-over-Cable Service Interface Specifications (DOCSIS) for use on cable networks.

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Contents

Prerequisites for Maximum CPE and Host Parameters for the Cisco CMTS Routers

The Maximum CPE and Host Parameters for the Cisco CMTS Routers feature is supported on the Cisco CMTS routers in Cisco IOS Release 12.3BC and 12.2SC. The table shows the hardware compatibility prerequisites for this feature.

Table 1 Maximum CPE and Host Parameters for the Cisco CMTS Hardware Compatibility Matrix

CMTS Platform

Processor Engine

Cable Interface Cards

Cisco uBR10012 Universal Broadband Router

Cisco IOS Release 12.2(33)SCA and later

  • PRE-2

Cisco IOS Release 12.2(33)SCB and later

  • PRE-4

Cisco IOS Release 12.2(33)SCH and later

  • PRE-5

Cisco IOS Release 12.2(33)SCA

  • Cisco uBR10-MC5X20S/U/H

Cisco IOS Release 12.2(33)SCC and later

  • Cisco UBR-MC20X20V

Cisco IOS Release 12.2(33)SCE and later

  • Cisco uBR-MC3GX60V1

Cisco uBR7246VXR Universal Broadband Router

Cisco IOS Release 12.2(33)SCA

  • NPE-G1
  • NPE-G2

Cisco IOS Release 12.2(33)SCA

  • Cisco uBR-MC28U/X
  • Cisco uBR-MC16U/X

Cisco uBR7225VXR Universal Broadband Router

Cisco IOS Release 12.2(33)SCA

  • NPE-G1

Cisco IOS Release 12.2(33)SCB and later

  • NPE-G2

Cisco IOS Release 12.2(33)SCA

  • Cisco uBR-E-28U
  • Cisco uBR-E-16U
  • Cisco uBR-MC28U/X
  • Cisco uBR-MC16U/X

Information About the MAX CPE and Host Parameters

The DOCSIS specification includes a number of provisions to allow service providers to control the number of subscribers who can access the network through any particular cable modem.

The following are the parameters that controls the number of CPE that can access the network:


Note
In addition, the DOCSIS configuration file contains a Network Access parameter that specifies whether the CPE devices behind the cable modem can access the cable network. If the Network Access parameter is set to Disabled, no CPE devices behind a cable modem are able to access the network.

Tip

Also, the Cisco CMTS lists offline cable modems in its internal database for 24 hours. The CMTS does not reset the CPE counts for these offline cable modems until the 24 hour period expires and the cable modems come back online. If the cable modems come back online before the 24 hour period expires, the CMTS continues to use the existing CPE counts.

All of these methods are similar in purpose, but they are configured differently and have a different impact on cable modems and their CPE devices.

The cable modem enforces the MAX CPE and MAC CPE IP values, and the CMTS enforces the MAX Host value. Because CPE devices can come online and offline at any time, it is important to understand how these different parameters interact, and how the cable modem and CMTS enforce them.


Note
The MAX CPE parameter provides Layer 2 control of CPE devices. The MAX CPE IP parameter provides Layer 3 control of CPE devices. The two methods are complimentary but not otherwise related.

MAX CPE

The MAX CPE is a required parameter and used to control the number of CPE devices that can access the network during the current session. In DOCSIS 1.0 cable networks, the MAX CPE parameter is the primary means of controlling the number of CPE devices that can connect to the cable network using any particular cable modem. This parameter is configured in the DOCSIS configuration file (TLV 18). If this parameter is not specified in the DOCSIS configuration file, it defaults to a value of 1.


Note
In DOCSIS 1.1 cable networks, the CMTS ignores the MAX CPE parameter that is specified in the DOCSIS configuration file, and uses the MAX CPE IP parameter instead.

Each time a new CPE device attempts to connect to the cable network, the cable modem logs the hardware (MAC) address. If the cable modem has not reached the MAX CPE number of MAC addresses, the new CPE device is allowed to access the network. If the cable modem has reached the MAX CPE limit, it drops the traffic from any additional CPE devices.

By default, the cable modem learns new MAC addresses on a first-come, first-served basis. You can also preconfigure the allowable MAC addresses for CPE devices by entering those MAC addresses in the DOCSIS configuration file (TLV 14). These cable modem gives these preconfigured MAC addresses preference in connecting to the network.

The DOCSIS specification does not allow cable modems to age out MAC addresses, so a MAC address stays in the log table of the cable modem until the cable modem is reset. You should therefore think of this parameter as specifying the maximum number of CPE devices that can connect during any particular session, instead of the maximum number of CPE devices that can simultaneously connect to the cable network.

For example, if you set MAX CPE to 2, a customer could use their cable modem to connect a maximum of two CPE devices (two MAC addresses) to the cable network. A customer could choose to connect two PCs simultaneously to their cable modem and use both to access the network.

However, if the customer then disconnected these PCs and connected two new PCs, the cable modem would not allow the new PCs to come online, because they would be the third and fourth MAC addresses that are connected to the cable modem. The customer would have to reset the cable modem before being able to use the new PCs.


Note
The MAX CPE value, if present, must be a positive integer in DOCSIS 1.0 configuration files. This parameter can be zero in DOCSIS 1.1 configuration files, but if so, the cable modem uses a MAX CPE value of 1. If the MAX CPE parameter is not present in either type of DOCSIS configuration file, it defaults to 1.

MAX CPE IP

The MAX CPE IP parameter is applicable only in DOCSIS 1.1 cable networks and is an optional parameter. This parameter specifies whether the cable modem should perform IP address filtering on the CPE devices. If so, this attribute also specifies the maximum number of simultaneous IP addresses that are permitted behind the modem at any one time.

The MAX CPE IP parameter is configured in the DOCSIS configuration file (TLV 35), or by using SNMP commands to set the docsDevCpeIpMax attribute (in DOCS-CABLE-DEVICE-MIB) for the cable modem. By default, this parameter is not enabled and the Cisco CMTS does not actively manage CPE devices, unless you enable the use of the MAX CPE IP parameter by using the cable submgmt default active command.


Note
In DOCSIS 1.1 networks, the CMTS ignores the MAX-CPE value (TLV 18) from the DOCSIS configuration file and uses the MAX CPE IP value instead.

If this feature is enabled, the cable modem learns the allowable IP addresses the first time that the CPE device sends an IP packet out into the network. The IP addresses are added to the docsDevFilterCpeTable table. This address table is cleared automatically when the cable modem is reset or powered off, or you can manually clear the IP address table by setting the docsSubMgtCpeControlReset attribute in the appropriate table entry for this cable modem.

In DOCSIS 1.1 networks, the MAX CPE IP parameter can be configured as follows:

  • If MAX CPE IP is set to –1, the cable modem does not filter any IP packets on the basis of their IP addresses, and CPE IP addresses are not added to the modem’s CPE address table
  • If MAX CPE IP is set to 0, the cable modem does not filter any IP packets on the basis of the IP addresses. However, the source IP addresses are still entered into the modem’s CPE address table.
  • If MAX CPE IP is set to a positive integer, it specifies the maximum number of IP addresses that can be entered into the modem’s CPE address table. The modem compares the source IP address for packets it receives from CPE devices to the addresses in this table. If a match is found, the packet is processed; otherwise, the packet is dropped.

Tip

In Cisco IOS Release 12.2(8)BC1, a similar address filtering mechanism exists on the CMTS. See the description of the docsSubMgtCpeControlMaxCpeIp attribute in the DOCS-SUBMGT-MIB MIB for details.

The CMTS uses the MAX CPE IP value as part of its own filtering process, but the two filters operate independently on the cable modem and CMTS.

MAX CPE IPv6

The MAX CPE IPv6 parameter is an optional parameter and specifies the maximum number of simultaneous IPv6 addresses that are permitted for a cable modem at any time.

The MAX CPE IPv6 parameter is configured in the DOCSIS 3.0 configuration file (TLV 63), or by using the SNMP commands to set the docsSubmgt3BaseCpeMaxIpv6PrefixDef attribute (in DOCS-SUBMGT3-MIB) for the cable modem. By default, this parameter is not enabled and the Cisco CMTS does not actively manage CPE devices, unless the use of the MAX CPE IPv6 parameter is enabled by using the cable submgmt default active command.

When the MAX CPE IPv6 feature is enabled, the cable modem learns the allowable IPv6 addresses the first time that the CPE device sends an IPv6 packet out into the network. The IPv6 addresses are added to the IPv6 address table. The address table is cleared automatically when the cable modem is reset or powered off.

In DOCSIS 3.0 networks, the MAX CPE IPv6 parameter can be configured as follows:

  • If MAX CPE IPv6 is set to 0, the cable modem filters any IPv6 packets on the basis of the IPv6 addresses. All the source IPv6 addresses are not entered into the CPE address table of the cable modem.
  • If MAX CPE IPv6 parameter is set to a positive integer, the parameter specifies the maximum number of IPv6 addresses that can be entered into the CPE address table of the cable modem. The modem compares the source IPv6 address for packets it receives from CPE devices to the addresses in this table. If a match is found, the packet is processed; otherwise the Cisco CMTS ignores the DHCPv6 packets from the CPE.

MAX Host

The MAX Host parameter is an optional parameter and is configured on the Cisco CMTS and specifies the maximum number of CPE devices (MAC addresses) that the CMTS will allow to have network access. You can control this parameter for individual cable modems, for all cable modems on a particular cable interface, or for all cable modems on the Cisco CMTS, depending on the CLI command being used:

  • cable modem max-hosts—Configures MAX Host for a particular cable modem.
  • cable max-hosts—Configures MAX Host for all cable modems on a particular cable interface.
  • cable modem max-cpe—Configures MAX Host for all cable modems on the Cisco CMTS. You can use the unlimited keyword to specify that the Cisco CMTS should not enforce a MAX Host limit for cable modems.

When this is enabled, the Cisco CMTS learns a MAC address the first time that the CPE device accesses the cable network. After the Cisco CMTS has logged the maximum number of MAC addresses specified by a MAX Host parameter, it drops all traffic from CPE devices that have any other MAC address.


Tip

In DOCSIS 1.1 cable networks, when both the MAX CPE IP and MAX Host parameters are configured, the Cisco CMTS uses the lesser value to determine the maximum number of CPE devices that are allowed behind each cable modem.


Note
The entire MAX Host address table is cleared whenever the Cisco TS is reset. You can also clear an entry for a particular CPE device using the clear cable host command.

Specifying MAX Host and MAX CPE Values

Typically, you would set the MAX Host parameter to a number that is greater than the value for the MAX CPE of the cable modem or MAX CPE IP parameter. This would allow customers to switch between multiple computers, without requiring them to reboot their cable modem, and without requiring any action on the part of the service provider’s network administrators.

For example, if you set MAX CPE or MAX CPE IP to a value of 2 for a cable modem, then you could set the MAX Host parameter to a value of 4. This would enable the cable modem to connect four different CPE devices to the cable network, but only two of them could be online simultaneously.

However, if you set the MAX Host parameter to a number smaller than the value of MAX CPE or MAX CPE IP in the DOCSIS configuration file, then the MAX CPE or MAX CPE IP value always takes precedence. For example, if the MAX CPE value is 2 and the MAX Host value is 1 , both the cable modem and CMTS allow up to two CPE devices to pass traffic for that cable modem.

Specifying an Unlimited Value for Max Host

The cable modem max-cpe command, which affects all cable modems on the CMTS, supports the unlimited keyword, which specifies that the CMTS should not enforce any limit on CPE devices. When you configure the CMTS with the unlimited keyword, this setting, you are allowing cable modems to support any number of CPE devices.

Do not use the unlimited option without also specifying the proper value for MAX CPE in the DOCSIS configuration file, so that each cable modem can control the maximum number of CPE devices it supports. In addition, to prevent users from requesting an unlimited number of IP address, be sure to configure the DHCP servers so that they control how many IP addresses are assigned to the CPE devices behind each cable modem.

Interoperation of the Maximum CPE Parameters

The different methods of CPE control can all be active simultaneously. They can interact with one another but do not conflict with one another. The table lists each method and compares their characteristics.

Table 2 Comparison of the Different Max CPE and Max Host Control Mechanisms

Method

Configuration Method

Function

Can Be Changed By...

Methods that are configured on the cable modem:

Network Access Control

DOCSIS Configuration File

Prevents all network access for CPE devices

Reset of cable modem

MAX CPE

DOCSIS Configuration File

Limits MAC addresses (Layer 2 control)

Reset of cable modem

MAX CPE IP

DOCSIS Configuration File SNMP Set Command

Limits IP addresses (Layer 3 control)

SNMP Set Command

Methods that are configured on the CMTS: 1

MAX CPE IP (the CMTS uses this value if MAX CPE IP is not specified in the DOCSIS configuration file)

DOCSIS Configuration File CLI Command SNMP Set Command

Limits IP addresses (Layer 3 control)

CLI Command SNMP Set Command

MAX Host Parameters

MAX Host for one cable modem (cable modem max-hosts)

CLI Commands

Limits CPE devices for one particular cable modem

New CLI Command

MAX Host for a cable interface (cable max-hosts)

Limits CPE devices for all cable modems on a particular cable interface

MAX Host for a CMTS (cable modem max-cpe)

Limits CPE devices for all cable modems on a Cisco CMTS

1 In Cisco IOS Release 12.2(4)BC1 and later releases, the Cisco CMTS does not actively manage CPE devices unless this has been enabled using the cable submgmt default active command.

The table lists the MAX CPE parameters in order of priority. For example, the Network Access Control and MAX CPE parameters interact as follows:

  • If the Network Access Control field for a cable modem is set to Disabled, none of that modem’s CPE devices will be able to access the network, regardless of how the other parameters are set.
  • If Network Access Control is Enabled and MAX CPE is set to 1 for a cable modem, then a maximum of one CPE device will be able to access the network, no matter how the remaining parameters are configured.

The table also lists the MAX Host parameters in order of more specific to less specific, where the more specific override the settings of the less specific. For example, if you use the cable modem max-cpe command to set the MAX Host value for all CMs to 2, you can still use the cable modem max-hosts command to give a particular CM a MAX Host value of 8.

In addition, the MAX CPE IP and MAX Host parameters interact as follows:

  • When both the MAX CPE IP parameter and the MAX Host parameter for a specific cable modem are specified, the CMTS uses the value specified for MAX Host for that particular modem.
  • When both the MAX CPE IP parameter and the MAX Host parameter for a cable interface are specified, the CMTS uses the larger value of the two.
  • When both the MAX CPE IP parameter and the MAX Host parameter for the CMTS are specified, the CMTS uses the smaller value of the two.

Tip
The Cisco CMTS keeps inactive cable modems listed in its internal database for 24 hours. The CMTS does not reset the CPE counts for these offline cable modems until the 24 hour period expires and the cable modems come back online. If the cable modems come back online before the 24 hours expires, the CMTS continues to use the existing CPE counts.

Possible Conflicts Between Parameters

The recommended procedure for disconnecting one PC from a cable modem and reconnecting a new one is the following:

  1. The user first releases the IP address assigned to the PC. The user can do this either by using a utility such as winipcfg, or by shutting down the PC.
  2. The user disconnects the old PC and reconnects the new PC to the cable modem.
  3. The user reboots the cable modem so as to clear out its MAX CPE values.
  4. After the cable modem has come online, the user boots the new PC so that it can obtain the correct IP address and come online.

This procedure allows the MAX CPE value on the cable modem to stay synchronized with the MAX Host value on the CMTS. Problems can occur in the following situations:

  • If the user does not release the IP address from the old PC before connecting a new one, the CMTS is not informed that the new PC is replacing the old one, and therefore counts both PCs when calculating the Host value. If the new value exceeds the MAX Host value, the CMTS does not allow the new PC to come online. The service provider has to issue the clear cable host command to remove the old PC from the MAX Host table, so as to allow the new PC to come online.
  • If the user does not reboot the cable modem after disconnecting the old PC, the cable modem retains the old PC’s MAC address and continues to count it when calculating the CPE value. If the new value exceeds the MAX CPE value, the cable modem does not allow the new PC to come online. The user has to reboot the cable modem before the new PC comes online.
  • If the user booted their PC before turning on the cable modem or before connecting the Ethernet cable to the cable modem. In this case, the operating system typically assigns a static private IP address (such as 169.254.232.199, which is the default Windows IP address). When the cable modem then boots or is connected to the PC, it logs the PC’s private IP address as one of the allowable IP addresses. So, if MAX CPE IP is set to 1, the PC will not be allowed access to the Internet. You must reboot the cable modem to clear its IP address tables, and allow the PC to acquire an IP address from the DHCP server. (To avoid this problem, set the docsDevCpeIpMax attribute for the cable modem to –1 in the DOCSIS configuration file. CableLabs has proposed –1 as the new default, but this change has not yet been given final approval or been implemented in current software releases.)

To reduce service-impacting problems when users replace PCs without following the above guidelines, service providers can configure the MAX Host parameter for a value greater than the MAX CPE value. This allows users to replace a limited number PCs without releasing the IP address and still be able to come online. (Users should continue to reboot the cable modem, however, because that is the only way to clear their internal CPE counter.)

For example, if you configure MAX CPE for a cable modem at 2, and MAX Host at 4, the user can connect any two PCs to the cable modem at any one time. The user can then replace both PCs with new PCs, reboot the cable modem, and have both PCs come online.

The CMTS CPE table for this cable modem lists all four PCs, and the user can switch between them at will, as long as the user reboots the cable modem after each switch. The user, however, is not allowed to bring a fifth PC online until one of the previous PCs has been cleared from the CMTS, using the clear cable host command.


Note
The cable modem always enforces the MAX CPE parameter, regardless of the setting of the other parameters.

Summary of CPE Address Control

In DOCSIS 1.1 cable networks, CPE address control is done as part of the following process, which also includes Layer 2 and Layer 3 filtering:

  1. MAC address filtering—Packets are filtered on the basis of the MAC address for the CPE device. The filter is controlled by the MAX CPE parameter, as set in the DOCSIS configuration file.
  2. Logical Link Control (LLC) filtering—Packets are filtered on the basis of the protocol for the packets. The filter is controlled by the docsDevFilterLLCTable table on the cable modem.
  3. CPE IP address filtering—Packets are filtered on the basis of the IP address for the CPE device, as controlled by the MAX CPE IP value, as well as the docsDevCpeIpMax attribute and the docsDevFilterCpeTable table on the CMTS.
  4. Access list filtering—Packets are filtered on the basis of access lists. IP filtering is controlled by the docsDevFilterIpTable table, and SNMP access filters are controlled by the docsDevNmAccessTable table.
  5. MAX Host control—The CMTS allows access for CPE devices on the basis of the MAX Host parameters.

Tip

This document does not describe the LLC and access list filtering. For more information about these filters, see the DOCS-CABLE-DEVICE-MIB MIB for more information on the SNMP attributes and tables that are listed above.

Benefits

  • CMTS flexibility allows multiple service operator provisioners, service providers, and other users to synchronize between the CMTS and the cable modem the maximum number of permitted CPE devices that can be connected behind a cable modem.
  • Changes can be made by using CLI commands or by using SNMP commands.

How to Configure the MAX CPE and Host Parameters

To reset the maximum number of permitted CPE devices recognized by the CMTS, use one of the following configuration commands. All procedures are optional, depending on the requirements.


Note
The CMTS assigns the MAX Host value to a cable modem at the time that the cable modem registers with the CMTS. Changing any of the MAX Host commands affects only cable modems that register after the change.

Configuring the Maximum Number of CPE Devices on the Cisco CMTS

To configure the maximum number of CPE devices per cable modem, use the following procedure:

     Command or ActionPurpose
    Step 1enable


    Example: 
    Router> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2configure terminal


    Example: 
    Router# configure terminal
     

    Enters global configuration mode.

     
    Step 3cable modem max-cpe [number | unlimited]

    Example: 
    Router(config)# cable modem max-cpe 8
     

    Sets the value of the MAX CPE parameter on the Cisco CMTS for all cable interfaces.

    If number is smaller than the MAX CPE value in the DOCSIS configuration file of the cable modem, this command overrides the configuration file value. If number is larger than the cpe-max value in the DOCSIS configuration file of the cable modem or or is set to unlimited, the value set in the configuration file takes precedence.

    Note    If the value in the configuration file is zero and no cable modem max-cpe is configured, then no CPE device is able to obtain an IP address.
     
    Step 4cable submgmt default active


    Example: 
    Router(config)# cable submgmt default active
     

    Specifies that the CMTS should actively manage CPE devices. The default is the no version of this command, so that the CMTS does not actively manage CPE devices.

    Note    This command is required before the Cisco CMTS manages the CPE devices when running a Cisco IOS Release 12.2 BC software image.
     
    Step 5cable submgmt default max-cpe cpe-num


    Example: 
    Router(config)# cable submgmt default max-cpe 4
     

    (Optional) Specifies the default value for the MAX-CPE parameter that the CMTS should use when the cable modem does not specify a MAX-CPE value in its DOCSIS configuration file.

     
    Step 6exit


    Example: 
    Router(config)# exit
     

    Exits global configuration mode.

     
    What to Do Next


    Note
    Use of the cable modem max-cpe unlimited command can open a security hole in the system by enabling denial of service attacks. It could allow a single user to obtain a large number of IP addresses, and thereby cause the entire network to go down after this single user has reserved all available IP addresses.

    Configuring the Maximum Number of Hosts for a Cable Interface

    Complete these steps to configure maximum number of hosts for a cable interface:

       Command or ActionPurpose
      Step 1enable


      Example: 
      Router> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.
       
      Step 2configure terminal


      Example: 
      Router# configure terminal
       

      Enters global configuration mode.

       
      Step 3interface cable x/y


      Example: 
      Router(config)# interface cable 4/0
       

      Enters cable interface configuration mode for the specified cable interface:

       
      Step 4cable max-hosts number


      Example: 
      Router(config-if)# cable max-hosts 10
       

      Specifies the maximum number of hosts that each cable modem on this cable interface can support.

       
      Step 5exit


      Example: 
      Router(config-if)# exit
       

      Exits interface configuration mode.

       
      Step 6exit


      Example: 
      Router(config)# exit
       

      Exits global configuration mode.

       

      Configuring the Maximum Number of Hosts for a Particular Cable Modem

      Complete these steps to configure the maximum number of hosts for a particular cable modem:

         Command or ActionPurpose
        Step 1enable


        Example: 
        Router> enable
         

        Enables privileged EXEC mode.

        • Enter your password if prompted.
         
        Step 2cable modem {mac-addr | ip-addr } max-hosts {number | default}

        Example: 
        Router# cable modem 000C.0102.0304 max-hosts 8
         

        Specifies the maximum number of hosts allowed behind this particular cable modem.

         

        Configuring the Maximum Number of IPv6 addresses for a Cable Modem on the Cisco CMTS

        Complete these steps to configure the maximum number of IPv6 addresses for a cable modem in Cisco CMTS:

           Command or ActionPurpose
          Step 1enable


          Example: 
          Router> enable
           

          Enables privileged EXEC mode.

          • Enter your password if prompted.
           
          Step 2configure terminal


          Example: 
          Router> configure terminal
           

          Enters global configuration mode.

           
          Step 3cable modem v6-max-cpe-prefix [n]

          Example: 
          Router(config)# cable modem v6-max-cpe-prefix 10
           

          Specifies the maximum number of IPv6 addresses for a cable modem on the Cisco CMTS for all cable interfaces.

           
          Step 4cable submgmt default active


          Example: 
          Router(config)#cable submgmt default
           

          Specifies that the CMTS should actively manage CPE devices. The default is the no form of this command, so that the CMTS does not actively manage CPE devices.

          Note    This command is required before the Cisco CMTS manages CPE devices when running a Cisco IOS Release 12.2 BC software image.
           
          Step 5exit


          Example: 
          Router(config)#exit
           

          Exits global configuration mode.

           

          Configuration Examples for the MAX CPE and Host Parameters

          The following example shows how to allow the CMTS to recognize a maximum of four CPE devices attached to online cable modems for a CMTS: 

          cable modem max-cpe 4

          The following example shows how to set the maximum CPE devices recognized by the CMTS for a cable interface to 15: 

          cable max-hosts 15

          The following example shows how to allow the CMTS to recognize a maximum of 30 attached CPE devices for a specific cable modem of IP address 172.172.172.12: 

          cable modem 172.172.172.12 max-hosts 30

          Configuration Examples

          To display the current configuration and status of a cable interface, use the show running-config command in privileged EXEC mode. The following is sample output that shows that the CMTS permits up to five CPE devices to use the specified cable interface to pass traffic. 

          interface Cable3/0
 ip address 192.168.1.1 255.255.255.0 secondary
 ip address 10.1.1.1 255.255.255.0
 load-interval 30
 no keepalive
 cable max-hosts 5
 cable downstream annex B
 cable downstream modulation 256qam
 cable downstream interleave-depth 32
 cable downstream frequency 507000000
 cable upstream 0 frequency 27008000
 cable upstream 0 power-level 0
 cable upstream 0 minislot-size 32
 cable upstream 0 modulation-profile 2
 no cable upstream 0 shutdown
 cable upstream 1 frequency 29008000
 cable upstream 1 power-level 0
 cable upstream 1 channel-width 3200000
 cable upstream 1 minislot-size 4
 no cable upstream 1 shutdown
 cable dhcp-giaddr policy
 cable helper-address 172.17.110.131
end

          You can also use the more system:running-config command to verify the maximum number of permitted CPE devices for a cable interface. 

          CMTS01# more system:running-config
Building configuration...
Current configuration:
!
interface Cable6/0
 ip address 1.1.1.1 255.255.255.0
 no keepalive
 cable max-hosts 4
 cable insertion-interval 2000
 cable downstream annex B
 cable downstream modulation 64qam
 cable downstream interleave-depth 32
 cable downstream symbol-rate 5056941
 cable upstream 0 frequency 15008000
 cable upstream 0 fec
 cable upstream 0 scrambler
 no cable upstream 0 shutdown

          You can use the show cable modem detail command to list information on each CPE device permitted for a cable modem. The command displays the max cpe value as configured in the DOCSIS configuration file for the cable modem, and in parentheses the value of n configured in the cable modem max-cpe command, if different. See the following sample output where the CMTS is configured for max-cpe equal to four and then max-cpe equal to unlimited: 

          test-cmts# show cable modem detail
 
Interface         SID MAC address   Max CPE Concatenation Rx SNR
Cable4/0/U0 1      0001.9659.47bb    1      yes           37.37
Cable4/0/U0 2      0001.9659.47ab    1      yes           33.70
Cable4/0/U0 3      0001.9659.47bf    1      yes           30.67
Cable4/0/U0 4      0001.9659.3ef7    1      yes           28.84
Cable4/0/U0 5      0001.9659.47eb    1      yes           30.89
test-cmts# conf t
Enter configuration commands, one per line. End with CNTL/Z.
test-cmts(config)# cable modem max-cpe ?
<1-255> Number
unlimited Max CPE not enforced
test-cmts(config)# cable modem max-cpe 4
test-cmts(config)# end
test-cmts#
00:05:11: %SYS-5-CONFIG_I: Configured from console by console
test-cmts# show cable modem detail
Interface        SID MAC address   Max CPE Concatenation Rx SNR
Cable4/0/U0 1      0001.9659.47bb .1 (4)        yes       37.00
Cable4/0/U0 2      0001.9659.47ab .1 (4)        yes       33.54
Cable4/0/U0 3      0001.9659.47bf .1 (4)        yes       30.70
Cable4/0/U0 4      0001.9659.3ef7 .1 (4)        yes       29.00
Cable4/0/U0 5      0001.9659.47eb .1 (4)        yes       30.92
test-cmts# conf t
Enter configuration commands, one per line. End with CNTL/Z.
test-cmts(config)# cable modem max
test-cmts(config)# cable modem max-cpe ?
<1-255> Number
unlimited Max CPE not enforced
test-cmts(config)# cable modem max-cpe unli
test-cmts(config)# cable modem max-cpe unlimited 
test-cmts(config)# ^Z
 
test-cmts#
00:06:06: %SYS-5-CONFIG_I: Configured from console by console
test-cmts# show cable modem detail
Interface      SID MAC address      Max CPE Concatenation Rx SNR
Cable4/0/U0 1      0001.9659.47bb   1 (ul)      yes          36.64
Cable4/0/U0 2      0001.9659.47ab   1 (ul)      yes          33.26
Cable4/0/U0 3      0001.9659.47bf   1 (ul)      yes          30.73
Cable4/0/U0 4      0001.9659.3ef7   1 (ul)      yes          29.15
Cable4/0/U0 5      0001.9659.47eb   1 (ul)      yes          30.95

          Additional References

          For additional information related to configuring the MAX CPE and Host parameters on the Cisco CMTS, refer to the following references:

          Related Documents

          Related Topic

          Document Title

          Cisco CMTS Commands

          Cisco CMTS Cable Command Reference

          Interaction of MAX CPE Parameters

          Using the max-cpe Command in the DOCSIS and CMTS

          Standards

          Standards2

          Title

          SP-RFIv1.1-I08-020301

          Data-Over-Cable Service Interface Specifications Radio Frequency Interface Specification , version 1.1 ( http:/​/​www.cablelabs.com/​cablemodem/​ )

          2 Not all supported standards are listed.

          MIBs

          MIBs3

          MIBs Link

          DOCS-CABLE-DEVICE-MIB

          DOCS-SUBMGT-MIB

          DOCS-SUBMGT3-MIB

          To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:

          http:/​/​www.cisco.com/​go/​mibs

          3 Not all supported MIBs are listed.

          Technical Assistance

          Description

          Link

          The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

          http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

          Feature Information for Maximum CPE and Host Parameters for the Cisco CMTS Routers

          Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http:/​/​tools.cisco.com/​ITDIT/​CFN/​. An account on http:/​/​www.cisco.com/​ is not required.


          Note

          The below table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

          Table 3 Feature Information for Maximum CPE and Host Parameters for the Cisco CMTS Routers

          Feature Name

          Releases

          Feature Information

          Maximum CPE and Host Parameters for the Cisco CMTS Routers

          12.0(6)SC

          This feature was introduced on the Cisco uBR7200 series universal broadband routers.

          Maximum CPE and Host Parameters for the Cisco CMTS Routers

          12.0(10)SC

          The cable modem max-cpe command was introduced for the Cisco uBR7200 series universal broadband routers.

          Maximum CPE and Host Parameters for the Cisco CMTS Routers

          12.1(2)EC1

          This feature was integrated into Cisco IOS Release 12.1(2)EC1.

          Maximum CPE and Host Parameters for the Cisco CMTS Routers

          12.1(5)EC

          Support was added for the Cisco uBR7100 series universal broadband routers.

          Maximum CPE and Host Parameters for the Cisco CMTS Routers

          12.2(4)BC1

          This feature was integrated into Cisco IOS Release 12.2(4)BC1 on the Cisco uBR7100 series, Cisco uBR7200 series, and Cisco uBR10012 universal broadband routers.

          Maximum CPE and Host Parameters for the Cisco CMTS Routers

          12.2(33)SCA

          This feature was integrated into Cisco IOS Release 12.2(33)SCA. Support for the Cisco uBR7225VXR Universal Broadband Router was added.

          TLV63 Support

          12.2(33)SCH1

          The cable modem v6-max-cpe-prefix command was introduced to limit the maximum number of IPv6 addresses per cable modem for the Cisco uBR10012 and Cisco uBR7200 series universal broadband routers.