Installation guide

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Cisco uBR7100 Series Universal Broadband Router Software Configuration Guide
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Chapter 3 Configuring the Cisco Cable Interface
Configuring DHCP Options
Current configuration:
!
interface Cable1/0
ip address 1.1.1.1 255.255.255.0
no keepalive
no cable proxy-arp
cable downstream annex B
cable downstream modulation 64qam
cable downstream interleave-depth 32
cable downstream symbol-rate 5056941
cable upstream 0 frequency 15008000
no cable upstream 0 shutdown
Tip If you are having difficulty with verification, make sure you entered the correct port and cable modem
card slot number when you activated cable proxy ARP.
Configuring DHCP Options
Activating Cable Relay Agent
The cable relay agent is for use with DOCSIS-based DHCP servers that utilize option 82 to automatically
map the Ethernet MAC address of a host (subscriber PC) with the cable interface to which it is
connected.
With the cable relay agent activated, the Cisco uBR7100 series CMTS inserts the cable interface MAC
address into a DHCP packet when the packet is received from a cable interface or another host. The
Cisco uBR7100 series CMTS then forwards the packet to the DHCP server.
To activate the cable relay agent, use the following command in cable interface configuration mode.
Tip If you are having difficulty with verification, make sure you entered the correct port and cable interface
card slot number when you activated the cable relay-agent-option.
Note A DOCSIS-based DHCP server is required. The DHCP server verifies that the defined IP address, if any,
returned to the host is valid for the IP subnet on that downstream interface. The IP address must be
unique and valid in the subnet for the subscriber to obtain connectivity.
Activating DHCP giaddr
Configure the Cisco uBR7100 series CMTS so it will either assign primary addresses to cable modems
and remote hosts, or assign primary addresses to cable modems and secondary addresses to remote hosts.
To configure cable DHCP giaddr functionality, use one of the following commands in cable interface
configuration mode.
Command Purpose
CMTS01(config)# cable relay-agent-option
Activate the cable relay agent. This is the default.