Cisco Systems uBR7200 manual Setting the Downstream Helper Address, MC-541

ip helper-address

Configuring Headend Broadband Access Router Features

Configuring the Downstream Cable Interface

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:

	Command	Purpose
Step 1
	CMTS01(config-if)#cable helper-address 10.x.x.x		Sets the downstream helper address to the DHCP
	cable-modem		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		Sets the downstream helper address to the DHCP
	host		server at IP address 172.56.x.x for UDP broadcast
			packets from hosts.

Verifying the Downstream Helper Address

To verify the downstream helper address setting, enter the show running-configcommand and look for 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.

Cisco IOS Multiservice Applications Configuration Guide

MC-541