Setting The Downstream Helper Address - Cisco 7246VXR - uBR Router Software Configuration Manual

Chapter 3 Configuring Cable Modem Interface Features
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Setting the Downstream Helper Address

Specify an IP address of a Dynamic Host Configuration Protocol (DHCP) server where User Datagram
Protocol (UDP) broadcast packets will be sent. You can specify a DHCP server for UDP broadcast
packets from cable interfaces, and a DHCP server for UDP broadcast packets from hosts. To set a
downstream helper address, use the following commands in cable interface configuration mode.
Command
Step 1
Router(config-if)# cable
helper-address 10.x.x.x
cable-modem
Step 2
Router(config-if)# cable
helper-address 172.56.x.x host
Verifying the Downstream Helper Address
To verify the downstream helper address setting, enter the show running-config command and look for
cable helper-address
Router# show running-config
Building configuration...
Current configuration:
!
interface cable5/0
ip address 10.254.254.254 255.0.0.0
no ip directed-broadcast
cable helper-address 192.168.1.1
no keepalive
Perform these steps if you are having difficulty with verification:
Step 1 Check the cables, upconverters, RF levels, and frequencies if the cable interfaces do not find a
downstream signal.
Check the cables, RF levels, and upstream frequencies, and enter a no shut command if the
Step 2
cable interfaces find a downstream signal, but not an upstream signal.
Check the provisioning servers.
Step 3
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Check DHCP options and the IP address of the Time-of-Day (ToD) server:
Step 4
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OL-2239-03
To remove rate limiting on the given downstream port, issue the cable downstream rate-limit
token-bucket command.
To enable rate limiting on the given downstream port using a weighted packet discard policing
algorithm and to assign a weight for the exponential moving average of loss rate value, issue the
cable downstream rate-limit weighted-discard 3 command. Acceptable values are 1 to 4.
in the cable interface configuration information:
Ping the DHCP server using the source IP address option—the primary IP address of a cable
interface.
Check IP routing if the cable interfaces acquire an RF upstream and downstream lock, but do not
stay up.
Ping the ToD server using the source IP address option.
Check IP routing.
Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
Configuring the Downstream Cable Modem Interface
Purpose
Set the downstream helper address to the DHCP server at IP
address 10.x.x.x for UDP broadcast packets from cable modems.
Note Use the IP address of the DHCP server. Both 10.x.x.x and
172.56.x.x are private ranges.
Set the downstream helper address to the DHCP server at IP
address 172.56.x.x for UDP broadcast packets from hosts.
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