#clear cable modem <mac> reset

[captpikel]

I was looking at the humble "clear cable modem <mac> reset" command and was wondering if anyone had further detail on what exactly happens when this command is issued. I know that this removes a cable modem from the mac maintenance message list, but I'm wondering whether this sends any information to a cable modem specifically. Like a reset packet or some sort of information telling the cable modem to reinitialize. The command reference says this command removes the modem from that mac maintenance list AND the modem resets. It reads two ways saying it removes it from the list and sends a reset packet, or just removes it from the list and then the modem resets from the lack of messages

So I was wondering if the reset is due to the lack of a maintenance message and/or some packet(s) sent to the modems IP address requesting it to reinitialize. If anyone knows what exactly happens, can someone provide some documentation on it? I couldn't find this answer on Cisco's site, and I can't really start trying debug options on a live system.

[Chieh Yu · Accepted solution]

Hi,

The way "clear cable modem reset" works is the CMTS removes the CM from its periodic ranging list. This means the CM will range but not get any ranging response. The CM will eventually hit its T4 timeout value and reset as per the DOCSIS Specification.

Here in my lab I reset the modem 0008.0e72.44ac. As you can see, the ranging request is received by CMTS but CMTS simply aborts any ranging response.

Mar  2 08:42:41.429 PST: Ranging CM 0008.0e72.44ac, SID 13 on I/f Cable5/1/0/U0
Mar  2 08:42:41.433 PST: Ranging request from 0008.0e72.44ac, SID 13 [13] on Interface Cable5/1/0/U0
Mar  2 08:42:41.433 PST: Timing error 0, power error 0.00dB, freq error 68(thres 125 adj 0) [sm per 14.993 sec]
Mar  2 08:42:41.433 PST: Ranging successful.
Mar  2 08:42:41.433 PST: Equalization coeff size 16
Equalization Coeff:
Mar  2 08:42:41.433 PST: FFFFFFC0 00000040
Mar  2 08:42:41.433 PST: 00000040 FFFFFFC0
Mar  2 08:42:41.433 PST: 00000000 00000080
Mar  2 08:42:41.433 PST: 00004000 00000000
RCDN-uBR10K-2#clear cable modem 8.0e72.44ac reset
RCDN-uBR10K-2#
Mar  2 08:42:41.433 PST: 00000040 FFFFFE00
Mar  2 08:42:41.433 PST: 00000000 000000C0
Mar  2 08:42:41.433 PST: 00000000 FFFFFF80
Mar  2 08:42:41.433 PST: FFFFFFC0 00000040
Mar  2 08:42:41.433 PST: Ca5/1/0/U0: Send RNG-RSP for 0008.0e72.44ac, SID 13, DS RFID 1201
Mar  2 08:42:41.765 PST: Modem 0005.5e48.d025: Host Ca5/1/0/U1: ds_channel_id 180, rfid 1201
Mar  2 08:42:42.785 PST: Modem 0007.0e02.cae1: Host Ca5/1/0/U3: ds_channel_id 180, rfid 1201
Mar  2 08:42:42.789 PST: Modem 0007.0e02.c84f: Host Ca5/1/0/U1: ds_channel_id 180, rfid 1201
Mar  2 08:42:43.025 PST: Ranging CM 0008.0e72.44ac, SID 13 on I/f Cable5/1/0/U0
Mar  2 08:42:43.025 PST: Ranging CM 0008.0e72.44ac, SID 13 on I/f Cable5/1/0/U0
Mar  2 08:42:43.029 PST: Ranging request from 0008.0e72.44ac, SID 13 [13] on Interface Cable5/1/0/U0
RCDN-uBR10K-2#
Mar  2 08:42:43.029 PST: Aborting ranging.
Mar  2 08:42:43.029 PST: Ca5/1/0/U0: Send RNG-RSP for 0008.0e72.44ac, SID 13, DS RFID 1201
Mar  2 08:42:43.029 PST: Ranging request from 0008.0e72.44ac, SID 13 [13] on Interface Cable5/1/0/U0
RCDN-uBR10K-2#
Mar  2 08:42:43.029 PST: Aborting ranging.

The CMTS does not send any sort of reset message to the CM for the reset command and simply waits for the CM to time out and reboot itself.

This behavior is defined in the DOCSIS specifications, here I've linked the latest D3.0 specs:

http://www.cablelabs.com/cablemodem/specifications/specifications30.html

Check out the MULPI spec, page 361 Figure 10-35 - You'll see if the modem hits T4 timeout (no ranging response) to eventually reinitialize its hardware.

HTH,

Jack

[shrihegd]

thanks for the reply !