DHCP Relay Option (DOCSIS Option 82)
DOCSIS Option82 modifies DHCPDISCOVER packets to distinguish cable interfaces from the CPE devices
or
“
clients
”
behind them. The DOCSIS Option82 is comprised of the following two suboptions:
•
Suboption 1, Circuit ID:
Type 1 (1 byte)
Len 4 (1 byte)
Value (8 bytes)
<bit 31,30,....................0)
<xYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY>
where the MSB indicates if the attached device is a cable interface.
x=1 Cable Modem REQ
x=0 CPE device (Behind the cable interface with the cable interface MAC address shown in suboption 2.)
The rest of the bits make up the SNMP index to the CMTS interface.
Y=0xYYYYYYY is the SNMP index to the CMTS interface.
•
Suboption 2, MAC address of the cable interface:
Type 2 (1 byte)
Len 6 (1 byte)
Value xxxx.xxxx.xxxx (6 bytes)
Overview of Scripts
This section lists the scripts applicable to cable interface configuration.
Two-way Cable Modem Scripts
To support two-way configurations at a subscriber site, use these scripts:
•
Relay.tcl
•
SetRouter.tcl
Telco Return Cable Modem Scripts
To support telco return and two-way cable interface configurations on the same cable interface card or chassis,
use these scripts:
•
PostClientLookup.tcl
•
PrePacketEncode.tcl
Cisco cBR Series Converged Broadband Routers Application
—
Voice and Video Configuration Guide
46
Cisco Network Registrar for the Cisco CMTS Routers
DHCP Relay Option (DOCSIS Option 82)
