Cisco SR2016T-NA Reference Manual page 54

cable dhcp-giaddr
Usage Guidelines You can use this command to modify the GIADDR field of DHCPDISCOVER and DHCPREQUEST
packets to provide a relay IP address before packets are forwarded to the DHCP servers. Use this
command to set a policy option such that primary addresses are used for CMs and secondary addresses
are used for hosts (such as PCs) behind the CMs.
When using multiple secondary subnets, the Cisco CMTS uses the first secondary IP address as the
GIADDR field when forwarding a DHCPDISCOVER request to the DHCP server. If no DHCP server
responds with a DHCPOFFER message after three attempts, the Cisco CMTS uses the next secondary
IP address, up to a maximum of 16 secondary addresses.
If you have configured a Cisco CM for routing mode and are also using the cable-modem dhcp-proxy
Note
nat command on the CM, you must configure the corresponding cable interface on the Cisco CMTS with
the cable dhcp-giaddr policy [strict] command.
Caution You cannot use the strict option with the internal DHCP server that is onboard the Cisco CMTS router,
because the strict option requires the use of DHCP relay operation, which is not performed by DHCP
termination points such as the internal DHCP server.
Examples The following example shows how to set the primary address to be used always for GIADDR:
Router# configure terminal
Router(config)# interface cable 3/0
Router(config-if)# cable dhcp-giaddr primary
Router(config-if)#
The following example shows how to set the primary address to be used always for giaddr in the cable
subinterface mode:
Router# configure terminal
Router(config)# interface cable 6/0.1
Router(config-subif)# cable dhcp-giaddr primary
Router(config-if)#
The following example shows how to configure the router so that the primary address is used for CMs
and the secondary addresses are used for hosts. In addition, the GIADDR is used as the source IP address
in forwarded DHCPOFFER packets.
Router# configure terminal
Router(config)# interface cable 5/1/0
Router(config-if)# cable dhcp-giaddr policy strict
Router(config-if)#
Related Commands Command
cable helper-address
cable relay-agent-option
cable source-verify
Cisco Broadband Cable Command Reference Guide
2-42
Description
Specifies a destination IP address for User Datagram
Protocol (UDP) broadcast (DHCP) packets.
Enables the system to insert the CM MAC address into a
DHCP packet received from a CM or host and forward the
packet to a DHCP server.
Turns on CM upstream verification.
Chapter 2 Cisco CMTS Configuration Commands
OL-1581-08