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alternety

join:2009-01-05

SB6120 continuously blinking activity light

A couple of days ago my SB6120 started to have the activity light blinking constantly. My first thought was that someone had taken over my PC. Not it.

Had Comcast look at the modem just for grins (I own it). Nothing seemed wrong. I tried moving cables around. Whenever I plug the modem in it behaves this way. Any port in the router. Any port in a switch with nothing else attached. Reset the router and set it up again. No change. The modem still seems to work correctly. I can access the internet.

Any ideas out there as to the cause/solution?


sashwa
Premium,Mod
join:2001-01-29
Alcatraz
kudos:17
I think the activity light blinking on the sb6120 is normal. The sb5100 does the same thing.

alternety

join:2009-01-05
No, it is not normal. In the several months I have had it this never occurred. It is actually communicating with the attached device. What is being said, I have no idea. The light displays activity.

taffeys

join:2009-11-30
Oceanside, CA
Yes, it is normal. I'm looking at a Motorola trouble-shooting guide for the SB6120 and it says this about the link light "Ready. PC/Activity is solid when a CPE is connected and blinks when transmitting or receiving data."

alternety

join:2009-01-05

1 edit
I am sorry. I do not seem to be getting this said correctly.

It is constantly communication some non-useful information back and forth to anything that is directly attached to it. The blinking light is not the problem. It is the data activity that the blinking light represents. After months of use with data transfers (as indicated by this light) being as expected (and correlating completely with activity on the PC) it has started talking to the router for no obvious purpose. No activity is propagated to other devices connected to the router. Just continuous useless noise to whatever port it is attached to. It is constant. Never stops. Never did it before.


Johkal
Cool Cat
Premium,MVM
join:2002-11-13
Happy Valley
kudos:10
Please post your signal levels & log entries.

alternety

join:2009-01-05

1 edit
I will go figure out if I can do that. I do not remember what the logon/password was since I assumed that when Comcast provisioned it I would be locked out.

However, the check I had Comcast do indicated good levels and they reported there was nothing wrong in their look at the modem.

Speedtest is showing normal results. Everything seems to be working just fine - except for the unknown exchanges.


Johkal
Cool Cat
Premium,MVM
join:2002-11-13
Happy Valley
kudos:10

alternety

join:2009-01-05
Downstream 1 dBmV on both channels.

Upstream 48 dBmV

Total Unerrored Codewords 3549669358 3549668952
Total Correctable Codewords 16 0
Total Uncorrectable Codewords 1533 2131

Jan 01 1970 00:00:31 3-Critical D05.0 TFTP failed - Request sent - No Response;CM-MAC=00:22:10:39:20:0b;CMTS-MAC=00:1d:70:b0:0e:b4;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:29 5-Warning D04.1 ToD request sent - No Response received;CM-MAC=00:22:10:39:20:0b;CMTS-MAC=00:1d:70:b0:0e:b4;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:03:08 3-Critical D02.0 DHCP FAILED - Request sent, No response;CM-MAC=00:22:10:39:20:0b;CMTS-MAC=00:1d:70:b0:0e:b4;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:02:29 3-Critical R02.0 No Ranging Response received - T3 time-out;CM-MAC=00:22:10:39:20:0b;CMTS-MAC=00:1d:70:b0:0e:b4;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:02:08 3-Critical D02.0 DHCP FAILED - Request sent, No response;CM-MAC=00:22:10:39:20:0b;CMTS-MAC=00:1d:70:b0:0e:b4;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:01:45 3-Critical R02.0 No Ranging Response received - T3 time-out;CM-MAC=00:22:10:39:20:0b;CMTS-MAC=00:1d:70:b0:0e:b4;CM-QOS=1.1;CM-VER=3.0;
Dec 03 2009 03:36:00 3-Critical R04.0 Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=00:22:10:39:20:0b;CMTS-MAC=00:1d:70:b0:0e:b4;CM-QOS=1.1;CM-VER=3.0;
Dec 03 2009 03:35:36 3-Critical T05.0 SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=00:22:10:39:20:0b;CMTS-MAC=00:1d:70:b0:0e:b4;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:46 3-Critical R02.0 No Ranging Response received - T3 time-out;CM-MAC=00:22:10:39:20:0b;CMTS-MAC=00:1d:70:b0:0e:b4;CM-QOS=1.1;CM-VER=3.0;
Dec 03 2009 03:24:33 3-Critical R04.0 Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=00:22:10:39:20:0b;CMTS-MAC=00:1d:70:b0:0e:b4;CM-QOS=1.1;CM-VER=3.0;

Firmware Name: SB6120-1.0.2.1-SCM00-NOSH
Boot Version: PSPU-Boot 1.0.0.4m1
Hardware Version: 1.0
Firmware Build Time: Jul 20 2009 20:04:47


Johkal
Cool Cat
Premium,MVM
join:2002-11-13
Happy Valley
kudos:10

1 recommendation

Keep an eye on your log entries for this:

"Critical D05.0 TFTP failed - Request sent - No Response"

If you see this reoccurring, post over in the "Comcast Direct Forum" so someone can address this.

»Comcast Direct
--
Write me up a 125.......I Can't Drive 55 »redrocker.com/ »cabowabo.com/

taffeys

join:2009-11-30
Oceanside, CA
reply to alternety
The modem is constantly receiving requests, when I look at my firewall log those requests occur all the time but my firewall blocks them.

alternety

join:2009-01-05
It is a significant change in the way the modem is working.

3 - 4 months: not doing this

Starting Wednesday night: doing this

What has changed? What does it mean? Is it indicative of a problem? How do I make it go back to what it was doing? Is the modem bad?

Two 05 level errors at uncorrelatable times would not seem to be the cause of this behavior. At least one of those is probably related to testing or power cycling.

alternety

join:2009-01-05
I have been searching about some more to see if I can get some idea why this is happening. A thought occurred to me. Could there have been a firmware update from Comcast that changed this behavior. Is there a config parameter that would alter the behavior of the modem in this way?


NoVA_CoxUser
Stand back from the cage -- The RF bites
Premium
join:2004-07-06
Alexandria, VA
reply to alternety
This behavior has come up over in the Cox forum and was always attributed to "ARP Requests"

If you search BBR and/or Google it ... you'll at least be able to see what's been discussed before.

Don't know if that's what you're seeing though.

Good luck.

alternety

join:2009-01-05
Thanks. I sure wish I had a net analyzer to see what the traffic is. ARP could make sense; but why did it just start? An interesting point was made in the Cox post: the traffic (estimated at 1GB/Mo on the post) counts against your monthly cap on that system. Comcast is rolling out a program you can log onto to see how much you have used. I don't remember what their cap is. But I think it is pretty high.

I also ran across a comment on a forum that said Comcast had told a user that the SB6120 V1 hardware had to be replaced. I wonder if there is an issue. Mine is V1.

alternety

join:2009-01-05
I just talked to Comcast again. They said there has been no firmware or configuration changes to my modem for months.


SJTUSUK

@comcast.net
Hey. My SB6120 just started this today (12/7/09). It worked normally before - the link light would stay solid until data passed through the modem - then it would flicker. Now, the light suddenly blinks about once per second even when there should be nothing going on. Speed tests to »speedtest.comcast.net are poor now. Speed tests to other test sites appear ok. When I called Comcast, they said not to trust their own test site. What a bunch of idiots. I have tried everything to figure this out and no luck yet. As long as the cable is connected to the modem and an ethernet connection is also attached, the stupid light blinks (no flickering anymore). Grrrrrr...... Comcast denies they have updated any firmware or have any network issues that could be causing. If I figure it out, I will post....


NoVA_CoxUser
Stand back from the cage -- The RF bites
Premium
join:2004-07-06
Alexandria, VA

3 edits
reply to alternety
said by alternety:

I just talked to Comcast again. They said there has been no firmware or configuration changes to my modem for months.
That really doesn't surprise me too much.

The entire HFC system is functionally just a pathway linking your IP router (or computer) to your cableco's IP router. The CMTS and modem are just "in-between" components.

So if it's on your ISP's network (on your particular subnet) ... your devices should see it.

So the real question would be, "What has changed on the ISP's network protocol-wise."

Good luck finding an answer to that one!

alternety

join:2009-01-05
At least they are consistent.

Since my last post I installed a net sniffer (Wireshark). First I disconnected the cable side of the modem and the blinking stopped. In my mind that indicated it was probably Comcast traffic. The traffic is as suggested above - ARPs. Continually asking who owns for assorted IPs that I presume are on my logical partition of their net. Comcast phone help has told me they do not constantly flood ARPs. They said nothing like that was happening on my segment. They said nothing had changed on Wednesday.

i have tried resetting the modem to factory defaults and rebooting. No change. It appears to simply be something is doing on purpose and either don't realize it or are simply denying. I was also told on one of the calls that there was no monthly cap on Comcast.

It is very annoying. It destroys the utility of that light. And it is just plain annoying to have it doing that in the corner of my eye.

sjtusuk - what area are you in? I am near Seattle.

alternety

join:2009-01-05
Looking at the ARP contents I am confused. The format in the info section is:

who has IP tell IP

I have looked up half a dozen of the IP addresses and they are all Comcast. I am guessing they are servers looking for modems, but do not understand why they would be doing that. The modem should announce itself when it is powered on rather than the network constantly hunting for someone to talk to.

Example IP pairs: 76.149.183.4 76.149.180.1
22.16.200.92 22.16.200.1


NoVA_CoxUser
Stand back from the cage -- The RF bites
Premium
join:2004-07-06
Alexandria, VA
Could it be other customer(s) on your WAN subnet?

After all, if you query your own public IP it'll come back as "Comcast" right?


SJTUSUK

@comcast.net
reply to alternety
The aggravation continues... I am in North Florida near Tallahassee, a long way from Seattle. ARP is beyond my expertise level, but if "servers are looking for modems", maybe this could be to apply modem firmware updates? - just an idea. Anyway, I am sure it is a Comcast issue, but they deny it. It doesn't make sense that my network works fine for months and then suddenly something changes one bright Monday morning with no explanation. The phone support I have been able to reach has been completely useless. The last person couldn't get me off the phone fast enough because they had no idea what to do and didn't even believe their own instructions. I am curious - are you able to run a speed test to "http://speedtest.comcast.net"? If so, do you get reasonable results? I don't - I get about 3mbps for download now where before I got between 12-16. Thanks...


SJTUSUK

@comcast.net
reply to alternety
downloadcmLogsData.htm.zip 2,726 bytes
Modem log info
More info. I don't know if this will help any, but I was able to save my modem's log info. I noticed the modem had only been up/connected for 30 minutes or so when I looked at this info this morning - that was weird to me. It should stay connected most all of the time. I don't know what this info means exactly, but I did notice that the modem's firmware version is newer than what has been tested/approved by Comcast. Hope this helps in some way...

alternety

join:2009-01-05
I thought about someone trying to look at other peoples modems. It is strange however that the tell IP changes a lot. If someone were looking around, I would expect to see a single IP as the tell, though there is no reason it could not change.

alternety

join:2009-01-05
I used speedtest to my closest server and used the Comcast speedtest to the closest offered point. They were both about the same speed and both were what they should be. I really would not expect them to have changed because of the ARPs. I have not seen any performance issues after the start of the ARPs.

Try Wiresnake and connect your PC directly to your modem. Be sure you have your firewall running in the PC. That will confirm you have what I have.


SJTUSUK

@comcast.net
Ok, I'll have to take my network down and go to the simple modem-PC config a little later in the week. Comcast is coming Friday afternoon. I am going to have the simple config in place before they get here so as to eliminate all the blaming of my cables, my router, my splitter, etc., etc.. Although, if things go as I expect, they will probably blame the SB6120 I bought off Amazon instead of leasing something through them. We'll see. If anything valuable comes out of that visit, I'll make sure I forward it your way. I am wondering if the link light behavior can be related somehow to the connection errors that have started showing up in my modem log...

alternety

join:2009-01-05
I looked at your log. I am not seeing that sort of stuff with any regularity.

Would it not be nifty if they could get the clock/calendar to match real time. It would make it a whole lot more useful to correlate an occurrence with other events.

I was trying to collect a list from people in the Comcast user forum that told me when the link light started blinking and their approximate location. The thread was locked because I should not have multiple postings. But that would be useful information to bring to Comcast.


SJTUSUK

@comcast.net
After I told them my signal strength was within tolerance and showed them my log messages, Motorola support instructed me to reset the modem to factory defaults and see if it corrects the light issue. I don't know why it would change in the first place and have to be corrected with this sort of drastic step. I also can't afford to lose my connectivity for the next day or so if I reset the modem as requested. Have you tried this to see if it helps?


Napsterbater
Meh
Premium,MVM
join:2002-12-28
Milledgeville, GA
Reviews:
·Windstream
reply to alternety
Just to add this from the outer thread.
said by Napsterbater:

You say the blinking light is a problem...

Are you getting the speed you pay for?

Is you latency in a acceptable range?

If yes to both whats the problem?

Cable networks act like a big Lan with hundreds of modems on it, Cable modems have the ability to keep the light from blinking on traffic not destined for you compute/router but in their default state they blink for everything, Maybe in this firmware update or config file update to didn't add that back in, again its not a problem, there is nothing to fix.
About the ARP request this is normal behavior on a LAN/Ethernet network (Cable networks mimic this behavior) read up on it here »en.wikipedia.org/wiki/Address_Re···Protocol , sniff traffic on your own LAN you will see the same thing, maybe not as many due to the fact you have less computers on your network then the cable network in your area.

And Ill tell you again having a blinking activity light is no sign of a problem.
--
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alternety

join:2009-01-05
reply to SJTUSUK
Yes I did reset the modem. I selected reset to factory defaults and rebooted. Worked fine but did not change the ARPs from being passed through to the LAN port. The light continues to blink.