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The following sections are provided:
You can configure your cable modem to act as a bridge or router. See Figure 1 and Figure 2. For more detailed description of these scenarios, see the "Configuration Scenarios" section.
CATV---Originally stood for Community Antenna Television. Now refers to any cable (coaxial/fiber) based system that provides television services.
Cable modem---Any device that modulates and demodulates digital data onto a CATV plant.
Cable router---A modular chassis-based router optimized for the data over CATV HFC applications.
Channel---A specific frequency allocation and bandwidth. Downstream channels used for television in the U. S. are 6 MHz wide.
CM---Cable modem.
CMTS---Cable Modem Termination System. Any DOCSIS compliant headend cable router, such as the Cisco uBR7246.
Downstream---The set of frequencies used to send data from a headend to a subscriber.
Headend---Central distribution point fora 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 link between the HFC system and any external data networks.
HFC---Hybrid fiber-coaxial (cable). Older CATV systems were provisioned using only coaxial cable. Modern systems use fiber transport from the headend to an optical node located in neighborhood to reduce system noise. Coax 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. The term host here refers to computer systems 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 representing the majority of homes in the U.S. and Canada who have decided to drive a standard with the goal of having interoperable cable modems.
MSO---Multiple System Operator
QAM---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---Modulation scheme used in the upstream direction. Supports two data bits per symbol.
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.
You have performed all the installation prerequisites as defined in the following publications:
The Cisco uBR904 cable modem supports the following:
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 Hierarchical Control 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 your PC.
When the cable modem is installed, and the connected PC is configured for IP and has DHCP services 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.
In this scenario, the cable modem acts as a bridge for up to three PCs plugged directly into three of the four Ethernet ports on the cable modem and the Internet connected via the coaxial cable. All three Ethernet ports are treated as one Ethernet interface by the Cisco IOS software. The IP address for the PC and the coaxial cable interface are in the same subnet.
You can set up your bridging solution using one of these methods:
The bridging configuration is the default configuration for the Cisco uBR904 cable modem.
This is a typical bridging configuration for a single PC connected to the cable modem. Note that the configuration for multiple PCs (maximum three) is the same.
version 11.3 no service pad no service password-encryption ! hostname Router ! ! no ip routing ! ! ! interface Ethernet0 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 dynamically included in cable interface configuration.
ip address 188.188.1.40 255.255.0.0 cable-modem downstream saved channel 699000000 34
In this scenario, the cable modem acts as a router to connect to existing networks behind it. A typical use would be if you are connecting the Cisco uBR904 cable modem directly to four PCs via the Ethernet ports or to an internal Ethernet hub, which is connected to an existing PC network.
The cable modem is automatically configured to use the IP address of the headend cable router as the cable modem's default IP gateway.
You can configure your cable modem to function like a router using one of the following methods:
The cable IP address and downstream channel are auto-configured:
! version 11.3 no service pad no service password-encryption ! hostname Router ! ! ! ! ! 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 188.188.1.40 255.255.0.0 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 0.0.0.0 188.188.1.1 ! line con 0 line vty 0 4 login ! end
Choose from the following tasks to connect the cable modem to the HFC network:
If your cable service provider is using a DHCP server, you do not need IP addresses for the PCs. Simply plug in the cables and turn on the cable modem.
To verify that the cable modem is configured for Plug-and-Play bridging, enter the show startup-config EXEC command. The configuration should look like this:
uBR904# show startup-config Building configuration... Current configuration: ! version 11.3 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
If you are using one or more PCs directly connected to your cable modem, you can change the cable modem from acting as a bridge to acting as a router. Note that you can use a maximum of three PCs directly connected to your cable modem in a bridging scenario but you can use four PCs directly connected to your cable modem in a routing scenario. See the section "Configuration Scenarios" for details on both these configurations.
Use the following steps to switch your cable modem from a bridging to a routing setup.
| Step | Command | Purpose | ||
|---|---|---|---|---|
| uBR904> enable uBR904# | Enter enable mode. You have entered enable mode when the prompt changes to | ||
| uBR904# configure terminal Enter configuration commands, one per line. End with CNTL/Z. uBR904(config)# | Enter global configuration mode. You have entered the global configuration mode when the prompt changes to | ||
| uBR904(config)# interface cable-modem 0 | Specify the cable modem interface. | ||
| uBR904(config-if)# no cable-modem compliant bridge uBR904(config-if)# exit | Turn off MCNS auto-configured bridging. | ||
| uBR904(config)# ip routing uBR904(config)# router rip uBR904(config-router)# network 188.188.0.0 uBR904(config-router)# network 4.0.0.0 uBR904(config-router)# exit | Configure IP routing using RIP. | ||
| uBR904(config)# interface cable-modem 0 uBR904(config-if)# ip rip receive v 2 uBR904(config-if)# ip rip send version 2 uBR904(config-if)# exit | Configure the RIP routing protocol on the cable modem interface. | ||
| uBR904(config)# interface ethernet 0 uBR904(config-if)# ip rip receive v 2 uBR904(config-if)# ip rip send version 2 | Configure the routing protocol on the Ethernet interface. | ||
| uBR904(config-if)# Ctrl-Z uBR904# %SYS-5-CONFIG_I: Configured from console by console | Return to enable mode. | ||
| uBR904# copy running-config startup-config uBR904# exit | Save the configuration changes to NVRAM so that they are not lost during resets, power cycles, or power outages. |
To verify that no bridging is configured, routing is enabled, and the routing protocol on the interfaces is configured, enter the show startup-config command:
uBR904# show startup-config Building configuration... Current configuration: ! version 11.3 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 188.188.1.42 255.255.0.0 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 188.188.0.0 ! ip default-gateway 188.188.1.1 ip classless ! line con 0 line vty 0 4 login ! end
However, you can customize the cable modem's interface configuration, which deviates from the default setting that ships with the modem. For example, you may need to specify a different compliant mode, modify the saved downstream channel setting and upstream power value, or enable a faster downstream search algorithm.
.
| Command | Purpose |
|---|---|
uBR904 enable uBR904# | Enter enable mode. |
uBR904# configure terminal Enter configuration commands, one per line. End with CNTL/Z. uBR904(config)# | Enter global configuration mode. |
uBR904(config)# interface cable-modem 0 | Specify cable modem interface 0. |
uBR904(config-if)# cable-modem compliant {bridge | reed-solomon} | Change to a different compliant mode. Your choices are bridge or reed-solomon. |
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 section provides new and changed commands for the Cisco uBR904 cable modem.
All other commands used with this feature are documented in the Cisco IOS Release 11.3 command references.
New commands:
Changed commands:
To specify different compliant modes on a cable modem interface, use the cable-modem compliant interface configuration command. Use the no form of this command to disable a compliant mode.
cable-modem compliant {bridge | reed-solomon}
bridge | Enables DOCSIS compliant bridging at startup. |
reed-solomon | Enables reed-solomon. |
Interface configuration
This command first appeared in Cisco IOS Release 11.3 NA.
This example shows how to enter this command:
uBR904#configure terminalEnter configuration commands, one per line. End with CNTL/Z.uBR904#interface cable-modem 0 router(config-if) cable-modem compliant bridge router(config-if)
cable-modem downstream saved channel
cable-modem fast-search
interface cable-modem
show bridge cable-modem
show dhcp
show interface cable-modem
To modify the saved downstream channel setting and upstream power value on a cable modem, enter the cable-modem downstream saved channel interface configuration command. Use the no form of this command to remove the saved settings, which will be resaved upon the next initialization cycle.
cable-modem downstream saved channel ds-frequency us-power
ds-frequency | Downstream channel frequency in Hz, which can be between 91000000 and 860000000. |
us-power | Upstream power of the last successfully ranged session. |
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 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 upon the next initialization cycle.
This command is only useful for development engineers.
This example shows how to disable the downstream frequency 91000000 and the upstream power level 33 dBmV from the downstream channel scan and upstream power adjustment.
uBR904#configure terminalEnter configuration commands, one per line. End with CNTL/Z.uBR904#interface cable-modem 0 router(config-if) no cable-modem downstream saved channel 91000000 33
cable-modem compliant
cable-modem fast-search
interface cable-modem
show bridge cable-modem
show dhcp
show interface cable-modem
To enable a faster downstream search algorithm on a cable modem, use the cable-modem fast-search interface configuration command. Use the no form of this command to disable the downstream fast search feature.
cable-modem fast-searchThere are no key words 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 may be some cases where this fast search algorithm may 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.
This example shows how to enter this command:
uBR904#configure terminalEnter configuration commands, one per line. End with CNTL/Z.uBR904#interface cable-modem 0 router(config-if) cable-modem fast-search
cable-modem compliant
cable-modem downstream saved channel
interface cable-modem
show bridge cable-modem
show dhcp
show interface cable-modem
To specify the cable interface on a cable modem, use the interface cable-modem global configuration command.
interface cable-modem number
number | The interface number inside the cable modem. |
Disabled.
Global configuration
This command first appeared in Cisco IOS Release 11.3 NA.
The following example brings up the cable modem interface 0 and displays the available configuration commands:
uBR904#configure terminalEnter configuration commands, one per line. End with CNTL/Z.uBR904#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
cable-modem compliant
cable-modem downstream saved channel
cable-modem fast-search
show bridge cable-modem
show dhcp
show interface cable-modem
To display the current DHCP settings on point-to-point interfaces, use the show dhcp privileged Privileged EXEC command.
show dhcp {server | lease}
server | Show known DHCP servers. |
lease | Show DHCP addresses leased from a server. |
Privileged EXEC
Following is sample output for the show dhcp lease Privileged EXEC command:
uBR904#show dhcp leaseTemp IP addr: 188.188.1.40 for peer on Interface: cable-modem0DHCP Lease server: 4.0.0.32, state: 3 BoundDHCP transaction id: 2431Lease: 3600 secs, Renewal: 1800 secs, Rebind: 3150 secsNext timer fires after: 00:58:01Retry count: 0 Client-ID: 0010.7b43.aa01
Following is sample output for the show dhcp server Privileged EXEC command:
uBR904#show dhcp serverDHCP server: ANY (255.255.255.255)Leases: 1Offers: 1 Requests: 2 Acks: 1 Naks: 0Declines: 0 Releases: 0 Bad: 0TIME0: 4.0.0.188, TIME1: 0.0.0.0Subnet: 255.255.0.0
Table 1 describes the 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 are declined by the proxy-client. |
Releases | Number of times IP addresses have been relinquished gracefully by the client. |
Bad | Number of bad packets received from wrong length, wrong field type, etc. |
Subnet | Subnet used by the DHCP server. |
cable-modem compliant
cable-modem downstream saved channel
cable-modem fast-search
interface cable-modem
ip address-pool
ip dhcp-server
peer default ip address
show bridge cable-modem
show interface cable-modem
To display bridging information on a cable modem, use the show bridge cable-modem Privileged EXEC command:
show bridge cable-modem number
number | Number for the corresponding cable modem interface. |
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:
cable-modem compliant
cable-modem downstream saved channel
cable-modem fast-search
interface cable-modem
show dhcp
show interface cable-modem
To display information about the cable modem's cable interface, use the show interface cable-modem EXEC command.
show interface 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 routing and bridging information pertaining to the cable interface. |
irb | (Optional) Displays routing and bridging information pertaining to the cable interface. |
EXEC
This command first appeared in Cisco IOS Release 11.3 NA.
Traffic passing through the cable modem interface is shown in the following example:
uBR904#show interface cable-modem 0cable-modem0 is up, line protocol is upHardware is BCM3220, address is 0010.7b43.aa01 (bia 0010.7b43.aa01)Internet address is 188.188.1.60/16MTU 1500 bytes, BW 27000 Kbit, DLY 1000 usec, rely 255/255, load 1/255Encapsulation , loopback not set, keepalive not setARP type: ARPA, ARP Timeout 04:00:00Last input 00:07:04, output 00:00:41, output hang neverLast clearing of "show interface" counters neverQueueing strategy: fifoOutput queue 0/40, 0 drops; input queue 0/75, 0 drops5 minute input rate 0 bits/sec, 0 packets/sec5 minute output rate 0 bits/sec, 0 packets/sec4495 packets input, 1153221 bytes, 0 no bufferReceived 8 broadcasts, 0 runts, 0 giants, 0 throttles0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort12841 packets output, 1708272 bytes, 0 underruns0 output errors, 0 collisions, 11 interface resets0 output buffer failures, 0 output buffers swapped out
The following example displays the number of packets and each protocol type passing through the cable modem interface.
uBR904#show int 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
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
Routing and bridging information on the cable modem interface is display 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
cable-modem compliant
cable-modem downstream saved channel
cable-modem fast-search
interface cable-modem
show bridge cable-modem
show dhcp
For additional software configuration information, refer to the following publications:
Posted: Thu Feb 25 11:49:47 PST 1999
Copyright 1989-1999©Cisco Systems Inc.