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)
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