Cisco SR2016T-NA Reference Manual page 293

Chapter 2 Cisco CMTS Configuration Commands
Some brands or models of cable modems might be running older software releases that cache the
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DOCSIS configuration file and use the cached version instead of downloading the actual file from
a TFTP server during the registration process. Although this can marginally speed up the registration
process, it also violates the DOCSIS requirements and could create a situation in which the cable
modem is not using the proper DOCSIS configuration file. A user might then be mistakenly accused
of theft-of-service, when in reality the problem is the non-DOCSIS-compliant cable modem.
The cable tftp-enforce command identifies these situations and can block these cable modems from
registering and coming online. This command also has a mark-only option that allows these cable
modems to come online, but it also identifies the cable modems so that the network administrators can
investigate the situation further before taking any action.
When the command is used without the mark-only option, cable modems that do not download a TFTP
file through the cable interface are blocked from registering and coming online. The following message
is displayed on the console when such a cable modem attempts to register:
06:53:57: %UBR7200-4-REGISTRATION_BEFORE_TFTP: Registration request unexpected:
Cable Modem did not attempt TFTP. Registration Rejected. CM Mac Addr <00ff.ff66.12fb>
The mark-only option allows cable modems that do not download the TFTP file to come online, but it
also prints a warning message on the console and marks the cable modem in the
command with a pound sign (#). The following message is displayed on the console when such a cable
modem registers with the Cisco CMTS.
06:53:57: %UBR7200-4-REGISTRATION_BEFORE_TFTP: Registration request unexpected:
Cable Modem did not attempt TFTP. Modem marked with #. CM Mac Addr <00ff.ff66.12fb>
Cisco recommends that you initially configure cable interfaces with the mark-only option, so that
Tip
potential problems are identified without immediately interfering with users' ability to come online.
After you identify and resolve these initial problems, reconfigure the cable interfaces without the mark-
only option to block problem cable modems that attempt to come online without downloading a valid
DOCSIS configuration file.
The default behavior is not to require the TFTP download through the cable interface with the
Cisco CMTS router. Each cable interface must be configured with this command to require the TFTP
download.
Note The cable tftp-enforce command cannot be used on subinterfaces or on non-cable interfaces.
Operation on the Cisco uBR10012 Router
In Cisco IOS Release 12.2(15)BC1 and later releases, the Cisco uBR10012 router can occasionally
allow a cable modem to temporarily come online before the system has received confirmation that the
cable modem has downloaded the proper DOCSIS configuration file. This situation can occur when the
cable interface line card receives a registration request (REG-REQ) message from a cable modem before
the PRE1 module has notified the line card whether the modem did download the proper file from the
TFTP server.
In previous Cisco IOS releases, these cable modems were not allowed to come online (or marked as
TFTP violators) even if they had successfully downloaded the appropriate DOCSIS configuration file.
In Cisco IOS Release 12.2(15)BC1 and later releases, however, the Cisco uBR10012 router allows these
cable modems to temporarily come online until the PRE1 module has finished determining the modem's
TFTP status. If the system determines that the modem did not download the appropriate DOCSIS
configuration file, it is then taken offline (or marked as a TFTP violator).
OL-1581-08
Cisco Broadband Cable Command Reference Guide
cable tftp-enforce
show cable modem
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