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The following sections are provided:
The Cisco uBR904 is a compact device that supports the direct connection of up to four PCs and has the familiar features and programming interface of other routers in Cisco's extensive line of small- and medium-sized business product offerings. The Cisco uBR904 provides packet data transport and network address translation for TCP/IP applications between home or office computers and the cable headend.
You can configure your cable modem to act as a bridge or as a router. See Figure 1 and Figure 2. For more detailed descriptions of these options, see the "Configuration Options" section.
The Cisco uBR904 cable modem provides the following benefits for data-over-cable applications:
CATV---Originally stood for Community Antenna Television. Now refers to any coaxial or fiber cable-based system that provides television services.
Cable modem (CM)---Any device that modulates and demodulates digital data onto a CATV plant.
Cable router---A modular chassis-based router optimized for data-over-CATV hybrid fiber-coaxial (HFC) applications.
Channel---A specific frequency allocation and bandwidth. Downstream channels used for television in the United States are 6 MHz wide.
CM---Cable modem.
CMTS---Cable Modem Termination System. Any DOCSIS-compliant headend cable router, such as the Cisco uBR7246.
DHCP---Dynamic Host Configuration Protocol. This protocol provides a mechanism for allocating IP addresses dynamically so that addresses can be reused when hosts no longer need them.
DOCSIS---Data Over Cable Service Interface Specification. Defines technical specifications for equipment at both subscriber locations and cable operators' headends.
Downstream---The set of frequencies used to send data from a headend to a subscriber.
Headend---Central distribution point for a CATV system. Video signals are received here from satellite (either co-located or remote), frequency converted to the appropriate channels, combined with locally originated signals, and rebroadcast onto the HFC plant. For a CATV data system, the headend is the typical place to create a link between the HFC system and any external data networks.
HFC---Hybrid fiber-coaxial (cable network). Older CATV systems were provisioned using only coaxial cable. Modern systems use fiber transport from the headend to an optical node located in the neighborhood to reduce system noise. Coaxial cable runs from the node to the subscriber. The fiber plant is generally a star configuration with all optical node fibers terminating at a headend. The coaxial cable part of the system is generally a trunk-and-branch configuration.
Host---Any end-user computer system that connects to a network. In this document, the term host refers to the computer system connected to the LAN interface of the cable modem.
MAC layer---Media Access Control sublayer. Controls access by the cable modem to the CMTS and to the upstream data slots.
MCNS---Multimedia Cable Network System Partners Ltd. A consortium of cable companies providing service to the majority of homes in the United States and Canada. This consortium has decided to drive a standard with the goal of having interoperable cable modems.
MSO---Multiple Service Operator. A cable service provider that also provides other services such as data and/or voice telephony.
QAM---Quadrature Amplitude Modulation. A method of modulating digital signals onto a radio-frequency carrier signal involving both amplitude and phase coding. QAM is a modulation scheme mostly used in the downstream direction (QAM-64, QAM-256). QAM-16 is expected to be usable in the upstream direction. Numbers indicate number of code points per symbol. The QAM rate or the number of points in the QAM constellation can be computed by 2 raised to the power of <number of bits/symbol>.
QPSK---Quadrature Phase-Shift Keying. A method of modulating digital signals onto a radio-frequency carrier signal using four phase states to code two digital bits.
Ranging---The process of acquiring the correct timing offset such that the transmissions of a cable modem are aligned with the correct mini-slot boundary.
SID (Service ID)---A number that defines (at the MAC sublayer) a particular mapping between a cable modem (CM) and the CMTS. The SID is used for the purpose of upstream bandwidth allocation and class-of-service management.
Subscriber Unit (SU)---An alternate term for cable modem. See cable modem.
Upstream---The set of frequencies used to send data from a subscriber to the headend.
The Cisco uBR904 cable modem is a standalone device; it works in conjunction with the Cisco uBR7246 universal broadband router.
In order to use the Cisco uBR904 cable modem for data-over-cable applications, the following conditions must be met:
The Cisco uBR904 cable modem supports the following:
The Cisco uBR904 has a single-cable F-connector interface for connection to the HFC network and a built-in Ethernet 10BaseT hub that provides four RJ-45 ports to which subscriber devices can be connected. All four ports are treated as one Ethernet interface by the Cisco IOS software. More hosts can be connected to the unit by connecting one of the 10BaseT ports to a hub. An additional RJ-45 port provides a console interface for configuration and diagnostic purposes.
In compliance with MCNS requirements, the cable interface requires no configuration or setup procedures other than connecting the Cisco uBR904 to the cable system. The unit is configured automatically using a configuration file generated by the cable service provider and delivered via the Cisco uBR7246 universal broadband router installed at the cable headend. The headend router provides a path from the cable modem to the DHCP server for PC address assignment.
The personal computer(s) connected to the cable modem must be configured for Internet Protocol (IP). In addition, the cable service provider must have a correctly configured network Dynamic Host Configuration Protocol (DHCP) server and EIA downstream channel. Using DHCP, the universal broadband router assigns an IP address to the cable modem each time it connects to the network. The IP address identifies the computer on the network and enables the universal broadband router to route data to and from the PC.
After the cable modem is installed and the connected PC is configured for IP, and after DHCP services are enabled and communication to the headend is established, the Cisco uBR7246 universal broadband router downloads configuration information to the cable modem. The initial configuration connection to the headend can take several minutes.
See Figure 3 for a sample network topology.
The Cisco uBR904 cable modem is usually configured automatically via a configuration file generated by the cable service provider; however, you can also manually configure the cable modem to function either as a bridge or as a router. The following sections give brief descriptions of both applications.
The Cisco uBR904 cable modem complies with the MCNS standards for interoperable cable modems; it supports full transparent bridging as well as DOCSIS-compliant transparent bridging.
In bridging applications, the Cisco uBR904 acts as a transparent bridge for up to three PCs plugged directly into three of the four Ethernet ports on the rear panel of the unit. The cable modem is connected to the Internet via the coaxial cable. All three Ethernet ports are treated as one Ethernet interface by the Cisco IOS software. The IP addresses for the PCs and the coaxial cable interface are in the same subnet.
DOCSIS-compliant transparent bridging is the default configuration of the Cisco uBR904 cable modem. If your cable service provider is using a DHCP server, all you need to do is connect the cables and power on the cable modem; your service provider's configuration program will automatically configure both the coaxial cable interface and the bridging functionality. You do not need to set up IP addresses for the attached PCs or enter any Command Line Interface (CLI) configuration commands. This type of operation is called plug-and-play bridging.
In addition to the plug-and-play method, you can configure a bridging application on the Cisco uBR904 using one of the following methods:
In this application, the cable modem acts as a router to connect to existing networks. A typical use would be if you are connecting the cable modem to an internal Ethernet hub that is connected to an existing PC network. You can also connect the cable modem directly to as many as four PCs via the Ethernet ports on the rear panel.
The cable modem is automatically configured to use the IP address of the Cisco uBR7246 headend cable router as the cable modem's default IP gateway.
You can configure the Cisco uBR904 cable modem to function like a router using one of the following methods:
The Cisco uBR904 cable modem typically is configured automatically on power-up using a configuration file generated by the cable service provider and delivered via the Cisco uBR7246 universal broadband router installed at the cable headend. All of the configuration tasks listed below are optional.
One of the first configuration tasks you might want to perform is to configure a host name and set an encrypted password. Configuring a host name allows you to distinguish multiple Cisco uBR904 cable modems from each other. Setting an encrypted password allows you to prevent unauthorized configuration changes.
To configure a host name and an encrypted password for a Cisco uBR904 cable modem, perform the following tasks, starting in global configuration mode:
To verify that you configured the correct host name and password, enter the show running-config command from global configuration mode:
cisco(config)# show running-config Using 1888 out of 126968 bytes ! version XX.X . . ! hostname cisco ! enable secret 5 $1$60L4$X2JYOwoDc0.kqa1loO/w8/
cisco# exit
cisco con0 is now available
Press RETURN to get started.
cisco> enable
Password: guessme
cisco#
If you are having trouble:
To assign an IP address to the Ethernet or cable modem interface so that it can be recognized as a device on the Ethernet LAN, perform the following tasks, starting in global configuration mode:
| Step | Command | Purpose |
|---|---|---|
| 1 | uBR904(config)# interface ethernet 0 or uBR904(config)# interface modem-cable0 uBR904(config-if)# | Enter interface configuration mode for the Ethernet and/or the cable modem interface. |
| 2 | uBR904(config-if)# ip address 172.16.1.1 255.255.255.0 | Assign the appropriate IP address and subnet mask to the interface. |
| 3 | uBR904(config-if)# Ctrl-Z uBR904# %SYS-5-CONFIG_I: Configured from console by console | Return to privileged EXEC mode.
This message is normal and does not indicate an error. |
To verify that you have assigned the correct IP address, enter the show arp command:
uBR904# show arp Protocol Address Age (min) Hardware Addr Type Interface Internet 172.16.1.1 - 0009.0613.6030 ARPA cable-modem0 Internet 4.0.0.28 - 00e0.1ed7.524d ARPA Ethernet0
If you are having trouble:
If you have one or more PCs directly connected to your cable modem, you can change the cable modem's configuration from bridging to routing. When configured as a bridge, the cable modem can have a maximum of three PCs directly connected; when configured as a router, it can have four PCs directly connected. See the "Configuration Options" section for details on both of these configurations.
To configure the Cisco uBR904 cable modem for routing, perform the following tasks, starting in global configuration mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| uBR904(config)#interface cable-modem0 | Enter interface configuration mode for the cable modem interface. | ||
| uBR904(config-if)#no cable-modem compliant bridge uBR904(config-if)#end | Turn off MCNS auto-configured bridging. | ||
| uBR904(config)#ip routing | Enable IP routing for the cable modem. | ||
| uBR904(config)#router rip | Enter router configuration mode and enable Routing Information Protocol (RIP) on the cable modem. | ||
| uBR904(config-router)#network network-number | Specify the network connected to the cable modem on which the RIP process will operate. If the cable modem is attached to more than one network, enter each IP address in a separate command. | ||
| uBR904(config-router)#end uBR904(config)#interface cable-modem0 | Exit router configuration mode. | ||
| uBR904(config-if)#ip rip receive v 2 | Specify that only RIP Version 2 packets will be received on the coaxial cable interface. | ||
| uBR904(config-if)#ip rip send v 2 | Specify that only RIP Version 2 packets will be sent on the coaxial cable interface. | ||
| uBR904(config-if)#end uBR904(config)#interface ethernet0 | Exit interface configuration mode for the cable modem interface and enter interface configuration mode for the Ethernet0 interface. | ||
| uBR904(config-if)#ip rip receive v 2 | Specify that only RIP Version 2 packets will be received on this Ethernet interface. | ||
| uBR904(config-if)#ip rip send v 2 | Specify that only RIP Version 2 packets will be sent on this Ethernet interface. | ||
| uBR904(config-if)#Ctrl-z uBR904#copy running-config startup-config | Return to privileged EXEC mode. |
To verify that bridging is not configured, routing is enabled, and that Routing Information Protocol is configured on the interfaces, enter the show startup-config command:
uBR904# show startup-config Building configuration... Current configuration: ! version 12.0 no service pad no service password-encryption service udp-small-servers service tcp-small-servers ! hostname ubR904 ! ! ip host sw-lab-fw 4.0.0.1 ip domain-name cisco.com ip name-server 171.69.209.10 clock timezone EST 2 ! ! interface Ethernet0 ip address 4.0.0.33 255.0.0.0 ip rip send version 2 ip rip receive version 2 no keepalive ! interface cable-modem0 ip address 172.16.1.42 255.255.0.0 ip rip send version 2 ip rip receive version 2 no keepalive cable-modem downstream saved channel 699000000 39 cable-modem downstream search-band 88 453000000 855000000 6000000 cable-modem downstream search-band 89 93000000 105000000 6000000 cable-modem downstream search-band 90 111250000 117250000 6000000 cable-modem downstream search-band 91 231012500 327012500 6000000 cable-modem downstream search-band 92 333015000 333015000 6000000 cable-modem downstream search-band 93 339012500 399012500 6000000 cable-modem downstream search-band 94 405000000 447000000 6000000 cable-modem downstream search-band 95 123015000 129015000 6000000 cable-modem downstream search-band 96 135012500 135012500 6000000 cable-modem downstream search-band 97 141000000 171000000 6000000 cable-modem downstream search-band 98 219000000 225000000 6000000 cable-modem downstream search-band 99 177000000 213000000 6000000 cable-modem downstream search-band 100 91000000 860000000 ! router rip network 4.0.0.0 network 172.16.0.0 ! ip default-gateway 172.16.1.1 ip classless ! line con 0 line vty 0 4 login ! end
The Cisco uBR904 cable modem is configured for bridging by default. If it becomes necessary to reconfigure the unit for bridging after it has been configured for routing, you can erase the routing configuration and return the unit to factory default configuration settings, or you can reconfigure the unit manually using the CLI. To return the cable modem to factory default settings, see the section "Reestablishing Plug-and-Play Bridging" for details. To reconfigure the cable modem manually, perform the following tasks, starting in global configuration mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| uBR904(config)#no service pad | Disable packet assembler/disassembler commands; prevent the uBR904 from accepting incoming or outgoing Packet Assembler/Disassembler (PAD) connections. | ||
| uBR904(config)#no service password-encryption | Disable password encryption. | ||
| uBR904(config)#no ip routing | Disable IP routing on the uBR904. | ||
| uBR904(config)#interface Ethernet0 | Enter interface configuration mode for the Ethernet0 interface. | ||
| uBR904(config-if)#no ip route-cache | Disable high-speed switching caches for IP routing. | ||
| uBR904(config-if)#bridge-group bridge-group | Assigns the Ethernet0 interface to a bridge group. The bridge group must be an integer between 1 and 63. | ||
| uBR904(config-if)#bridge-group bridge-group spanning-disabled | Disable spanning tree on the Ethernet interface. | ||
| uBR904(config-if)#end uBR904(config)#interface cable-modem0 | Exit interface configuration mode for the Ethernet0 interface and enter interface configuration mode for the cable modem interface. | ||
| uBR904(config-if)#no ip address | Disable the IP address of the coaxial cable interface, if one has been set. The uBR7246 cable router assigns an IP address to the cable modem each time it connects to the network. | ||
| uBR904(config-if)#no ip route-cache | Disable high-speed switching caches for IP routing on the cable interface. | ||
| uBR904(config-if)#no keepalive | Disable keepalives on the cable interface. | ||
| uBR904(config-if)#bridge-group bridge-group | Assign the cable modem interface to a bridge group. The bridge group must be an integer from 1 to 63. (The default is 59.) | ||
| uBR904(config-if)#bridge-group bridge-group spanning-disabled | Disable spanning tree on the cable interface. | ||
| uBR904(config-if)#end uBR904(config)#ip classless | Exit interface configuration mode. (Optional) At times, the uBR904 might receive packets destined for a subnet of a network that has no network default route. This global configuration mode command allows the Cisco IOS software to forward such packets to the best network route possible. | ||
| uBR904(config)#line console 0 | Enter line configuration mode to configure the console port. | ||
| uBR904(config-line)#line vty 0 4 | Identify the last line in a contiguous group of virtual terminals you want to configure. | ||
| uBR904(config-line)#Ctrl-z uBR904#copy running-config startup-config | Return to privileged EXEC mode. |
When the cable interface comes up, the IP address and downstream channel are configured automatically.
To verify that routing has been disabled on all interfaces and that bridging has been reenabled, enter the show startup-config command from privileged EXEC mode:
uBR904# show startup-config Building configuration... Current configuration: ! version 12.0 no service pad no service password-encryption ! hostname uBR904 ! no ip routing ! interface Ethernet0 no ip address no ip route-cache bridge-group 59 bridge-group 59 spanning-disabled ! interface cable-modem0 no ip address no ip route-cache no keepalive cable-modem downstream saved channel 699000000 36 bridge-group 59 bridge-group 59 spanning-disabled ! ip classless ! line con 0 line vty 0 4 login ! end
| Step | Command | Purpose | ||
|---|---|---|---|---|
| uBR904#erase startup config | Erase the current configuration (assuming the current running configuration has been saved to NVRAM). |
After entering this command, perform a warm reset of the Cisco uBR904 cable modem by pressing and holding down the Reset button for less than 10 seconds. For information on the location and operation of the Reset button, refer to the "Physical Description" section in the chapter "Installing the Cisco uBR904 Cable Modem" in the Cisco uBR904 Cable Modem Installation and Configuration Guide.
To verify that the cable modem is configured for Plug-and-Play bridging, enter the show startup-config command from privileged EXEC mode. The configuration should look like this:
uBR904# show startup-config Building configuration... Current configuration: ! version 12.0 no service pad no service password-encryption ! hostname uBR904 ! no ip routing ! interface Ethernet0 no ip address no ip route-cache bridge-group 59 bridge-group 59 spanning-disabled ! interface cable-modem0 no ip address no ip route-cache no keepalive cable-modem downstream saved channel 699000000 36 bridge-group 59 bridge-group 59 spanning-disabled ! ip classless ! line con 0 line vty 0 4 login ! end
However, you can customize the cable modem's interface configuration if you need to deviate from the default setting that ships with the modem. For example, you might need to specify a different compliant mode, modify the saved downstream channel setting and upstream power value, or enable a faster downstream search algorithm.
To customize the cable modem interface, perform the following tasks, starting in global configuration mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| uBR904(config)#interface cable-modem 0 | Specify cable modem interface 0. | ||
| uBR904(config-if)#cable-modem compliant bridge | Enable DOCSIS-compliant bridging. | ||
| uBR904(config-if)#cable-modem downstream saved channel ds-frequency us-power | Modify the saved downstream channel setting and upstream power value. If you do this, you must specify an exact downstream frequency and a power value.1 | ||
| uBR904(config-if)#cable-modem fast-search | Enable a faster downstream search algorithm. |
| 1Use the no cable-modem downstream saved channel ds-frequency us-power command to remove a saved frequency and power setting from NVRAM. |
This is a typical bridging configuration for a single PC connected to the Cisco uBR904 cable modem. Note that the configuration for multiple PCs (maximum of three) is the same.
version 12.0 no service pad no service password-encryption ! hostname uBR904 ! ! no ip routing ! ! ! interface Ethernet0 no ip address no ip route-cache bridge-group 59 bridge-group 59 spanning-disabled ! interface cable-modem0 no ip address no ip route-cache no keepalive bridge-group 59 bridge-group 59 spanning-disabled ! ip classless ! line con 0 line vty 0 4 login ! end
When the cable interface is up, the following lines are included in cable interface configuration:
ip address 172.16.1.40 255.255.0.0 cable-modem downstream saved channel 699000000 34
This is a typical routing configuration for the Cisco uBR904 cable modem. Note that the cable IP address and downstream channel are configured automatically.
! version 12.0 no service pad no service password-encryption ! hostname uBR904 ! ! ! ! ! interface Ethernet0 ip address 4.0.0.33 255.0.0.0 ip rip send version 2 ip rip receive version 2 ! interface cable-modem0 ip address 172.16.1.40 255.255.0.0 ip rip send version 2 ip rip receive version 2 no keepalive cable-modem downstream saved channel 699000000 34 no cable-modem compliant bridge ! router rip network 4.0.0.0 network 188.188.0.0 ! ip classless ip route 0.0.0.0 0.0.0.0 172.16.1.1 ! line con 0 line vty 0 4 login ! end
This section describes new and changed commands for the Cisco uBR904 cable modem for Cisco IOS Release 12.0(3)T.
All other commands used with this feature are documented in the Cisco IOS Release 12.0 command references.
To enable DOCSIS-compliant transparent bridging for a cable modem interface at startup, use the cable-modem compliant command from interface configuration mode. Use the no form of this command to disable DOCSIS-compliant bridging for the interface.
cable-modem compliant bridgeThis command has no arguments or keywords.
Enabled
Interface configuration
This command first appeared in Cisco IOS Release 11.3 NA.
It is normally not necessary to enter this command in data-over-cable bridging applications because DOCSIS-compliant bridging is enabled by default. If you wish to do full transparent bridging rather than DOCSIS-compliant bridging, use the no form of the command, then configure full transparent bridging using CLI commands. See the "Configuring Bridging" section for instructions.
The following example shows how to enter the cable-modem compliant bridge command for a cable modem interface, starting from global configuration mode:
uBR904(config)# interface cable-modem 0
uBR904(config-if)# cable-modem compliant bridge
uBR904(config-if)#
cable-modem downstream saved channel
cable-modem fast-search
cable-modem upstream preamble qpsk
interface cable-modem
To modify the saved downstream channel setting and upstream power value on a cable modem interface, enter the cable-modem downstream saved channel command from interface configuration mode. Use the no form of this command to remove the saved settings, which will be resaved at the next initialization cycle.
cable-modem downstream saved channel ds-frequency us-power
ds-frequency | Downstream channel frequency in Hz, which can be from 91000000 to 860000000. |
us-power | Upstream power level in decibels per millivolt (dBmV), which can be from 8 to 61. |
Enabled
Interface configuration
This command first appeared in Cisco IOS Release 11.3 NA.
This command is auto-generated by the operation of the cable MAC layer process. The MCNS DOCSIS RFI specification requires that cable modems remember the downstream frequency and upstream power of the last successfully ranged session. These parameters are called up as the first downstream frequency and upstream power to use the next time the cable modem is booted. This operation dramatically speeds up the channel search.
Use the no cable-modem downstream saved channel ds-frequency us-power command to remove the saved frequency and power setting from the running configuration, which will be resaved at the next initialization cycle.
Cisco recommends that this command NOT be used by end users of the Cisco uBR904 cable modem.
The following example shows how to remove the downstream frequency of 91000000 Hz and the upstream power level of 33 dBmV from the running configuration of a cable-modem interface, starting from global configuration mode.
uBR904(config)# interface cable-modem 0
uBR904(config-if)# no cable-modem downstream saved channel 91000000 33
uBR904(config-if)#
cable-modem compliant bridge
cable-modem fast-search
cable-modem upstream preamble qpsk
interface cable-modem
To enable a faster downstream search algorithm on a cable modem interface, use the cable-modem fast-search command from interface configuration mode. Use the no form of this command to disable the downstream fast-search feature.
cable-modem fast-searchThere are no keywords or arguments for this command.
Disabled
Interface configuration
This command first appeared in Cisco IOS Release 11.3 NA.
This feature speeds up the frequency search performed by the cable modem. Normally it takes the cable modem about 30 to 50 seconds to sample 30 to 50 frequencies. The cable-modem fast-search command can reduce this search time. However, there might be some cases where this fast-search algorithm might not perform as well as the default algorithm. Trial and error is the only way to discover how well this feature works for your environment.
The following example shows how to enter the cable-modem fast-search command, starting from global configuration mode:
uBR904(config)# interface cable-modem 0
uBR904(config-if)# cable-modem fast-search
uBR904(config-if)#
cable-modem compliant bridge
cable-modem downstream saved channel
cable-modem upstream preamble qpsk
interface cable-modem
To enable the QPSK modulation scheme in the upstream direction from the cable modem interface to the headend, enter the cable-modem upstream preamble qpsk command from interface configuration mode. Use the no form of this command to disable upstream modulation for the interface.
cable-modem upstream preamble qpskThis command has no arguments or keywords.
Enabled
Interface configuration
This command first appeared in Cisco IOS Release 11.3 NA.
The following example shows how to enter the cable-modem upstream preamble qpsk command for a cable modem interface, starting from global configuration mode:
uBR904(config)# interface cable-modem 0
uBR904(config-if)# cable-modem upstream preamble qpsk
uBR904(config-if)#
cable-modem compliant bridge
cable-modem downstream saved channel
cable-modem fast-search
interface cable-modem
To specify the cable modem interface on a Cisco uBR904 cable modem, enter the interface cable-modem command from global configuration mode.
interface cable-modem number
number | The interface number of the cable-modem interface on the rear panel of the cable modem. |
Disabled
Global configuration
This command first appeared in Cisco IOS Release 11.3 NA.
When this command is entered, the Cisco cable modem switches from global configuration mode to interface configuration mode.
The following example brings up cable modem interface 0 and displays the available cable-modem interface configuration commands:
uBR904(config)#interface cable-modem 0uBR904(config-if)# cable-modem ? compliant Enter compliant modes for interface downstream Downstream channel characteristics fast-search Enable/disable the DS fast search upstream upstream channel characteristics uBR904(config-if)#
cable-modem compliant bridge
cable-modem downstream saved channel
cable-modem fast-search
cable-modem upstream preamble qpsk
To display bridging information for a cable modem, enter the show bridge cable-modem command from privileged EXEC mode.
show bridge cable-modem number
number | The interface number of the cable-modem interface on the rear panel of the cable modem. |
Privileged EXEC
This command first appeared in Cisco IOS Release 11.3 NA.
Following is a sample output for this command:
uBR904#show bridge cable-modem 0Total of 300 station blocks, 298 freeCodes: P - permanent, S - selfBridge Group 59:
Table 1 describes the significant fields shown in the display.
| Field | Description |
|---|---|
Total of 300 station blocks | Total number of forwarding database elements in the system. The memory to hold bridge entries is allocated in blocks of memory sufficient to hold 300 individual entries. When the number of free entries falls below 25, another block of memory sufficient to hold another 300 entries is allocated. Thus, the total number of forwarding elements in the system is expanded dynamically, as needed, limited by the amount of free memory in the router. |
Bridge Group | The number of the bridge group to which this interface is assigned. |
show dhcp
show interfaces cable-modem
To display the current DHCP settings on point-to-point interfaces, enter the show dhcp command from privileged EXEC mode.
show dhcp {lease | server}
lease | Show DHCP addresses leased from a server. |
server | Show known DHCP servers. |
Privileged EXEC
You can use this command on any point-to-point type of interface that uses DHCP for temporary IP address allocation.
Following is sample output for the show dhcp lease command:
uBR904#show dhcp leaseTemp IP addr: 188.188.1.40 for peer on Interface: cable-modem0Temp sub net mask: 0.0.0.0DHCP Lease server: 4.0.0.32, state: 3 BoundDHCP transaction id: 2431Lease: 3600 secs, Renewal: 1800 secs, Rebind: 3150 secsTemp default-gateway addr: 188.188.1.1Next timer fires after: 00:58:01Retry count: 0 Client-ID: 0010.7b43.aa01
Table 3 describes the significant fields shown in the display.
| Field | Description |
|---|---|
Temp IP addr | IP address leased from the DHCP server for the cable modem interface. |
Temp subnet mask | Temporary subnet mask assigned to the cable modem interface. |
DHCP Lease server | IP address of the DHCP server that assigned an IP address to this client. |
state | Current state of this client (the cable modem interface). Possible states are Bound, Renew, or Rebinding. For descriptions of these states, see RFC 2131. |
DHCP transaction id | Unique number established by the uBR904 before the first request message is sent to the DHCP server. The same transaction id is used as long as the lease keeps getting renewed and is valid. If a new "discover" message is sent, a new transaction id is used. |
Lease | Time (in seconds) for which the leased IP address is valid; the duration of the lease. |
Renewal | Time interval (in seconds) from address assignment until the client transitions to the renewing state. When the renewal (T1) time expires, the client sends a unicast dhcprequest message to the server to extends its lease. The default value of this timer is 0.5 times the duration of the lease. |
Rebind | Time interval (in seconds) from address assignment until the client transitions to the rebinding state and sends a broadcast dhcprequest message to any DHCP server to extends its lease. The default value of this timer (T2) is 0.875 times the duration of the lease. |
Temp default-gateway addr | IP address of the router closest to this client on the network. |
Next timer fires after | Time in hours, minutes, and seconds until the next timer expires. |
Retry count | Number of times the client has sent any message to the DHCP server -- most likely a request message to extend its lease. When the lease is renewed, the Retry count is reset to 0. |
Client-ID | MAC address (with optional media type code) that uniquely identifies the client on the subnet for binding lookups. |
Following is sample output for the show dhcp server command:
uBR904#show dhcp serverDHCP server: ANY (255.255.255.255)Leases: 1Offers: 1 Requests: 2 Acks: 1 Naks: 0Declines: 0 Releases: 0 Bad: 0TFTP Server Name: SOHOSERVERTIME0: 1.2.0.250, TIME1: 0.0.0.0 Subnet: 255.255.255.0
Table 3 describes the significant fields shown in the display.
| Field | Description |
|---|---|
DHCP server | MAC address used by the DHCP server. |
Leases | Number of current leased IP addresses. |
Offers | Number of offers for an IP address sent to a proxy-client from the server. |
Requests | Number of requests for an IP address to the server. |
Acks | Number of `acknowledge' messages sent by the server to the proxy-client. |
Naks | Number of `not acknowledge' messages sent by the server to the proxy-client. |
Declines | Number of offers from the server that have been declined by the proxy-client. |
Releases | Number of times IP addresses have been relinquished gracefully by the client. |
Bad | Number of bad packets received due to wrong length, wrong field type, or other causes. |
TFTP Server Name | Name (if any) configured for the server providing TFTP downloads to the cable modem. |
TIME0 | IP address of the primary Time of Day (TOD) server. |
TIME1 | IP address of the secondary Time of Day (TOD) server. |
Subnet | Subnet containing the DHCP server. |
interface cable-modem
ip address-pool
ip dhcp-server
peer default ip address
show bridge cable-modem
show interfaces cable-modem
To display information about the Cisco uBR904 cable modem's cable interface, enter the show interfaces cable-modem command from either user EXEC mode or privileged EXEC mode.
show interfaces cable-modem number [accounting | counters | crb | irb | type]
number | Cable modem interface number. |
accounting | (Optional) Displays the number of packets of each protocol type that has been sent through the cable modem interface. |
counters | (Optional) Shows MIB counters on the cable interface. |
crb | (Optional) Displays concurrent routing and bridging information for each interface that has been configured for routing or bridging. This option does not really apply to the uBR904; it is included because it is part of the subsystem that provides DOCSIS-compliant bridging. For more information, refer to the Bridging and IBM Networking Command Reference. |
irb | (Optional) Displays integrated routing and bridging information for each interface that has been configured for routing or bridging. This option does not really apply to the uBR904; it is included because it is part of the subsystem that provides DOCSIS-compliant bridging. For more information, refer to the Bridging and IBM Networking Command Reference. |
type | (Optional) Designed to display information about virtual LANs associated with the interface; however, this option is not supported on the uBR904. |
User EXEC or privileged EXEC
This command first appeared in Cisco IOS Release 11.3 NA.
When this command is entered without a keyword, general information about the cable interface is displayed.
Traffic passing through the cable modem interface is shown in the following example:
uBR904#show interfaces cable-modem 0cable-modem0 is up, line protocol is upHardware is BCM3220, address is 0010.7b6b.7821 (bia 0010.7b6b.7821)Internet address is 172.16.1.60/16MTU 1500 bytes, BW 27000 Kbit, DLY 1000 usec, reliablility 255/255, txload 1/255, rxload 1/255 Encapsulation DOCSIS, loopback not set, keepalive not set ARP type: ARPA, ARP Timeout 04:00:00Last input 00:07:04, output 00:00:41, output hang neverLast clearing of "show interface" counters never Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 4495 packets input, 1153221 bytes, 0 no buffer Received 8 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 12841 packets output, 1708272 bytes, 0 underruns 0 output errors, 0 collisions, 11 interface resets 0 output buffer failures, 0 output buffers swapped out
Table 4 describes the significant fields shown in the display.
| Field | Description |
|---|---|
cable-modem0 is up | Indicates that the interface is currently active. "Disabled" indicates the interface has received more than 5000 errors in one keepalive interval (10 seconds by default if keepalive is set); "administratively down" indicates the interface has been taken down by an administrator. |
line protocol is up | Indicates that the software processes that handle the line protocol believe the interface is usable. |
Hardware | Hardware type and MAC address. |
Internet address | Internet address followed by the shorthand notation for the subnet mask. |
MTU | Maximum Transmission Unit (equivalent of the maximum packet size) for the interface. |
BW | Bandwidth of the interface in kilobits per second. |
DLY | Delay of the interface in microseconds. |
reliability | Reliability of the interface, expressed as a fraction of 255, calculated as an exponential average over a 5-minute period. (255/255 equals 100% reliability.) |
tx load/rx load | Load on the interface caused by transmitting and receiving, expressed as a fraction of 255, calculated as an exponential average over a 5 minute period. |
Encapsulation/loopback/keepalive | Encapsulation method assigned to the interface. |
loopback | Indicates whether or not loopback is set. |
keepalive | Indicates whether or not keepalives are set. |
ARP type | Type of Address Resolution Protocol configured for the interface. |
ARP Timeout | Number of hours, minutes, and seconds an ARP cache entry will stay in the cache. |
Last input/output | Number of hours, minutes, and seconds since the last packet was successfully received/transmitted by the interface. |
output hang | Number of hours, minutes, and seconds since the interface was last reset because of a transmission that took too long. When the number of hours in any of the "Last.." fields exceeds 24, the number of days and hours is displayed. If the field overflows, asterisks are printed. |
Last clearing of "show interface" counters | Time at which the counters that measure cumulative statistics (such as number of bytes transmitted and received) shown in this report were last reset to zero. Note that variables that might affect routing (for example, load and reliability) are not cleared when the counters are cleared. *** indicates the elapsed time is too large to be displayed. |
Queueing strategy | Type of queueing strategy in effect on the interface. |
Output queue/drops | Number of packets in the output queue followed by the size of the queue and the number of packets dropped due to a full queue. |
input queue/drops | Number of packets in the input queue followed by the size of the queue and the number of packets dropped due to a full queue. |
5 minute input rate | Average number of bits and packets received and transmitted per second in the last 5 minutes. If the interface is not in promiscuous mode, it senses network traffic it sends and receives (rather than all network traffic). The 5-minute input and output rates should be used only as an approximation of traffic per second during a given 5-minute period. These rates are exponentially weighted averages with a time constant of 5 minutes. A period of four time constants must pass before the average will be within two percent of the instantaneous rate of a uniform stream of traffic over that period. |
packets input | Total number of error-free packets received by the system. |
bytes input | Total number of bytes, including data and MAC encapsulation, in the error-free packets received by the system. |
no buffer | Number of received packets discarded because there was no buffer space in the main system. Compare with ignored count. Broadcast storms on Ethernet networks and bursts of noise on serial lines are often responsible for no input buffer events. |
Received broadcasts | Total number of broadcast or multicast packets received by the interface. |
runts | Number of packets discarded because they were smaller than the medium's minimum packet size. For example, any Ethernet packet less than 64 bytes is considered a runt. |
giants | Number of packets discarded because they were larger than the medium's maximum packet size. For example, any Ethernet packet larger than 1518 bytes is considered a giant. |
throttles | Number of times the receiver on the port was disabled, possibly due to buffer or processor overload. |
input errors | Includes runts, giants, no buffer, CRC, frame, overrun, and ignored counts. Other input-related errors can also cause the input errors count to be increased, and some datagrams may have more than one error; therefore, this sum may not balance with the sum of enumerated input error counts. |
CRC | Number of cyclic redundancy checksums generated by the originating LAN station or far-end device that do not match the checksum calculated from the data received. On a LAN, this usually indicates noise or transmission problems on the LAN interface or the LAN bus itself. A high number of CRCs is usually the result of collisions or a station transmitting bad data. |
frame | Number of packets received incorrectly, having a CRC error and a noninteger number of octets. On a LAN, this is usually the result of collisions or a malfunctioning Ethernet device. |
overrun | Number of times the receiver hardware was unable to hand received data to a hardware buffer because the input rate exceeded the receiver's ability to handle the data. |
ignored | Number of received packets ignored by the interface because the interface hardware ran low on internal buffers. These buffers are different from the system buffers mentioned previously in the buffer description. Broadcast storms and bursts of noise can cause the ignored count to be increased. |
abort | Number of packets whose receipt was aborted. |
packets output | Total number of messages transmitted by the system. |
bytes | Total number of bytes, including data and MAC encapsulation, transmitted by the system. |
underruns | Number of times the transmitter has been running faster than the router can handle. |
output errors | Sum of all errors that prevented the final transmission of datagrams out of the interface being examined. Note that this may not balance with the sum of the enumerated output errors, as some datagrams might have more than one error, and others might have errors that do not fall into any of the specifically tabulated categories. |
collisions | Number of messages retransmitted due to an Ethernet collision. This is usually the result of an overextended LAN (Ethernet or transceiver cable too long, more than two repeaters between stations, or too many cascaded multiport transceivers). A packet that collides is counted only once in output packets. |
interface resets | Number of times an interface has been completely reset. This can happen if packets queued for transmission were not sent within several seconds. On a serial line, this can be caused by a malfunctioning modem that is not supplying the transmit clock signal, or by a cable problem. If the system notices that the carrier detect line of a serial interface is up, but the line protocol is down, it periodically resets the interface in an effort to restart it. Interface resets can also occur when an interface is looped back or shut down. |
output buffer failures | Number of times the output buffer has failed. |
output buffers swapped out | Number of times the output buffer has been swapped out. |
To display the number of packets and bytes of each protocol type passing through the cable modem interface, use the accounting option with the show interface cable-modem command:
uBR904#show interface cable-modem 0 accountingcable-modem0Protocol Pkts In Chars In Pkts Out Chars OutIP 545 185502 159 90240Trans. Bridge 3878 964995 12597 1611142ARP 73 3066 86 4128
Table 5 describes the fields shown in this display.
| Field | Description |
|---|---|
Protocol | List of protocols operating on the cable-modem interface. |
Pkts In | Number of packets of each protocol received on the interface. |
Chars In | Number of bytes of each protocol received on the interface. |
Pkts Out | Number of packets of each protocol transmitted on the interface. |
Chars Out | Number of bytes of cach protocol transmitted on the interface. |
MIB counters on the cable interface are displayed in the next example:
uBR904#show int cable-modem 0 countersCable specific counters:Ranging requests sent : 50982Downstream FIFO full : 0Re-requests : 7277DS MAC Message Overruns: 0DS Data Overruns : 0Received MAPs : 254339485Received Syncs : 53059555Message CRC failures : 0Header CRC failures : 1394Data PDUs : 5853DS MAC messages : 307861745Valid Headers : 307869065Sync losses : 0Pulse losses : 1BW request failures : 6
Table 6 describes the counters shown in this display.
| Field | Description |
|---|---|
Ranging requests sent | Number of ranging requests sent by the uBR904 to the CMTS. |
Downstream FIFO full | Number of times the downstream input first-in first-out (FIFO) buffer became full on the uBR904. |
Re-requests | Number of times a bandwidth request generated by the uBR904 was not responded to by the CMTS. |
DS MAC Message Overruns | Number of times the uBR904's DMA controller had a downstream MAC message and there were no free MAC message buffer descriptors to accept the message. |
DS Data Overruns | Number of times the uBR904's DMA controller had downstream data and there were no free data PDU buffer descriptors to accept the data. |
Received MAPs | Number of times a MAP message passed all filtering requirements and was received by the uBR904. |
Received Syncs | Number of times a timestamp message was received by the uBR904. |
Message CRC failures | Number of times a MAC message failed a cyclic redundancy (CRC) check. |
Header CRC failures | Number of times a MAC header failed its 16-bit CRC check. The MAC header CRC is a 16-bit Header Check Sequence (HCS) field that ensures the integrity of the MAC header even in a collision environment. |
Data PDUs | Total number of data PDUs (protocol data units) of all types received by the uBR904. |
DS MAC messages | Number of MAC messages received by the uBR904. |
Valid Headers | Number of valid headers received by the uBR904, including PDU headers, MAC headers, and headers only. |
Sync losses | Number of times the uBR904 lost timebase sync with the CMTS. |
Pulse losses | Number of times the uBR904 did not receive expected timestamp messages from the CMTS. |
BW request failures | Number of times the uBR904 sent the maximum number of re-requests for bandwidth allocation and the request was still not granted. |
Information about routing and bridging protocols and filtering on the cable modem interface is displayed in the following example:
uBR904#show int cable-modem 0 crbcable-modem0Bridged protocols on cable-modem0:ipSoftware MAC address filter on cable-modem0Hash Len Address Matches Act Type0x00: 0 ffff.ffff.ffff 3877 RCV Physical broadcast0x2A: 0 0900.2b01.0001 0 RCV DEC spanning tree0x7A: 0 0010.7b43.aa01 573 RCV Interface MAC address0xC2: 0 0180.c200.0000 0 RCV IEEE spanning tree0xC2: 1 0180.c200.0000 0 RCV IBM spanning tree
Table 7 describes the software MAC address filter information for the cable modem interface.
| Field | Description |
|---|---|
Hash | Hash key/relative position in the keyed list for this MAC address filter. |
Len | Length of this entry to the beginning element of this hash chain. |
Address | Canonical (Ethernet ordered) MAC address of this filter. |
Matches | Number of received packets that match this MAC address. |
Act | Action to be taken when this address is looked up; choices are to receive or discard the packet. |
Type | MAC address type. |
cable-mocem compliant bridge
cable-modem downstream saved channel
cable-modem fast-search
show bridge cable-modem
interface cable-modem
For additional software configuration information and related documentation, refer to the following publications:
Posted: Thu Feb 3 16:52:09 PST 2000
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