Part 2 - Fifty Shades of DOCSIS Device Management
Auto Provisioning Overview
DHCP
DHCP provides IP addresses as well as other network and provisioning configuration parameters for CM, MTA, and CPE. These configuration parameters may include the default router, time server, DNS server, log server, hostname, domain name, TFTP server, configuration file name, lease time, ACS-URL, etc.
Both DOCSIS cable modems and PacketCable MTA adapters obtain their IP address and other configuration parameters via DHCP.
CMTS is a DHCP relay agent. It directs the DHCP packets to one or more previously configured DHCP servers. Information about the relay agent can be obtained from the giaddr field in DHCPv4 or from the link address or in the relay forward message DHCPv6.
DHCPv4 Option 122 is a CableLabs client configuration parameter that consists of several sub-options that control the MTA provisioning process.
DHCPv6 Option 17 is a CableLabs client configuration parameter that consists of several sub-options that provide configuration for Cable Modem and MTA. It contains sub-options, like TFTP Servers (32), configuration file name(33), etc.
DHCPv4 Option 60
The Vendor Class ID classifies the device that is requesting the configuration information. This parameter helps to differentiate one type of device from another.
This option is mandatory for both CMs and MTAs.
For cable modem - "docsisX.Y:*"
For MTA - “pktcX.Y:*”
For CPE - “eRouter”, other value or nothing.
See the example below:
DHCPv6 Option 16
The Vendor Class Identifier is important when we want to determine if the device is a DOCSIS cable modem, PacketCable MTA, or personal computer. The option is required for both CM and MTA.
DHCPv4 Option 43
Vendor Specific Information is used to transmit specific information for a particular vendor.
DHCPv6 Option 17
DHCPv4 Option 82
This option is inserted by the CMTS (DHCP relay agents) when forwarding requests to DHCP servers. The information in this option can be used during assigning IP addresses.
Option 82 includes several sub-options
Sub-option #1 is the circuit ID of the agent
Sub-option #2 is the agent's remote ID - in a cable network, it identifies the MAC Address of the cable modem from which the DHCP request was initiated
DHCPv6 Option 17, sub-option - CL_CM_MAC_ADDR (1026)
In the case of DHCPv6, in a relay-forward message, there is vendor option 17 with sub-option 1026 containing the CM MAC Address of the Cable Modem. If the DHCPv6 message was sent by a CPE or MTA and forwarded through a cable modem, this option will be added by a relay and contains the MAC address of the cable modem
TFTP
TFTP - Trivial File Transfer Protocol (RFC 1350) is used for data transfer. TFTP uses UDP and, in particular, port 69. The configuration file or firmware files for cable modems or MTAs are transferred using TFTP.
Note: From performance, reliability, and bandwidth standpoints, for big files like firmware, it is better to use HTTP file server.
DNS
TCP/IP applications use the Domain Name System (DNS) database, which contains information about hosts on the network to map IP addresses to domain names. In this case, port 53 will be used.
Time-of-Day Protocol (ToD)
The Time-of-Day (ToD) protocol is a high-resolution real-time measurement mechanism suitable for specifying the date and time of day for client devices. It uses UDP and port 37.
The address of the ToD server can be provided by option 4 for DHCPv4 or option 17 sub-option 37 (RFC868_SERVERS) for DHCPv6 during cable modem initialization.
The cable modem sends a request to the ToD server to get the current date and time.
The DHCPv4 option 2 and DHCPv6 option 17 sub-option 38(CL_OPTION_TIME_OFFSET) provide a time offset from GMT. Or it is also possible to specify a time zone via option 100 DHCPv4 or option 41 DHCPv6.
System logging (syslog)
Cable modems and MTA may use syslog messages to send information, such as event notifications, like status of provisioning.
DHCP Server provides the address of syslog server via option 7 (DHCPv4) and option 17 sub-option 34(CL_OPTION_SYSLOG_SERVERS) (DHCPv6). This option is mandatory for the MTA. For disabling syslog logging, the option may contain 0.0.0.0 or FF.FF.FF.FF.
The syslog protocol uses UDP for data transmission and port 514.
Simple Network Management Protocol (SNMP)
The SNMP Server protocol allows to monitor, control network performance, and change the configuration of the cable modems and MTA.