DHCP Fields and Options for Cable Modems
DHCP options and packet fields are required to enable cable modems to boot and operate properly. Table
below lists the required DHCP options and fields.
Table 6: Required DHCP Fields and Options
Value/DescriptionField/Option In Cisco Network
Registrar
Required Field/Option
Fields
IP address. As a DHCP packet
passes through the relay agent to
the DHCP server, the relay agent
supplies a unique IP address to the
packet and stores it in this field.
The relay agent is a cBR-8 router
with the iphelper attribute defined.
-giaddr
Subnet mask for the IP address
stored in the giaddr field. This
value is also stored in the DHCP
packet by the relay agent.
-subnet-mask
Name of the cable modem
configuration file that will be read
from a TFTP server.
Packet-file-namefile
IP address of the TFTP server
where configuration files are
stored.
Packet-siaddrsiaddr
Options
List of hosts running the time
server specified in the RFC 868
standard.
-Time-servers
Time offset of a cable modem
internal clock from Universal Time
Coordinated (UTC). This value is
used by cable modems to calculate
the local time that is stored in
time-stamping error logs.
-Time-offset
IP address of the security server.
This should be set if security is
required. See RFC 1533 for details.
-MCNS-security-server
Cisco cBR Series Converged Broadband Routers Application—Voice and Video Configuration Guide
42
Cisco Network Registrar for the Cisco CMTS Routers
DHCP Fields and Options for Cable Modems
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