Configuring Headend Broadband Access Router Features
Configuring the Downstream Cable Interface
MC-541
Cisco IOS Multiservice Applications Configuration Guide
Setting the Downstream Helper Address
Specify an IP address of a DHCP server where UDP broadcast (DHCP) packets will be sent. You can
specify a DHCP server for UDP broadcast packets from cable modems and a DHCP server for UDP
broadcast packets from hosts.
To set a downstream helper address, use one of the following commands in cable interface configuration
mode:
Verifying the Downstream Helper Address
To verify the downstream helper address setting, enter the show running-config command and look for
ip helper-address in the cable interface configuration information:
CMTS01# show running-config
Building configuration...
Current configuration:
!
interface Cable4/0
ip address 10.254.254.254 255.0.0.0
no ip directed-broadcast
ip helper-address 192.168.1.1
no keepalive
Troubleshooting Tips
To troubleshoot the configuration, perform the following tasks:
• If the cable modems do not find a downstream: check the cables, upconverters, RF levels, and
frequencies.
• If the cable modems find a downstream but not an upstream: check the cables, RF levels, and
upstream frequencies, and enter the no shut command.
• If the cable modems acquire an RF upstream and downstream lock, but do not stay up: check the
provisioning servers; ping the DHCP server using the source IP address option (the primary
IP address of a cable interface); check IP routing.
Command Purpose
Step 1
CMTS01(config-if)# cable helper-address 10.x.x.x
cable-modem
Sets 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.
Step 2
CMTS01(config-if)# cable helper-address 172.56.x.x
host
Sets the downstream helper address to the DHCP
server at IP address 172.56.x.x for UDP broadcast
packets from hosts.
