constant cable modem activity?


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i have comcast cable and i noticed that my sufboard cable modem led is always flashing with pc activity, even when my pc is turned off? maybe i never noticed this before but i wonder why it does that, any ideas? i am not behind a router either, i checked under my firewall and the only program active is scvhost atm.

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if it does not affect you then i would not worry about it. mine does it and it does not affect me in any way.

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Do you have a router between the cable modem and your PC? They'll frequently "chat".

Another possibility, especially if you have an unsecured wireless access point, is that you have a neighbor stealing bandwidth.

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Do you have a router between the cable modem and your PC? They'll frequently "chat".

Another possibility, especially if you have an unsecured wireless access point, is that you have a neighbor stealing bandwidth.

no router at all.

if it does not affect you then i would not worry about it. mine does it and it does not affect me in any way.

i want to make sure im not being charged by my cable provider for data that i did not download or use, that's why i asked. i don't remember the led flashing constantly, i did also recently notice my internet / torrent speeds are a ton faster than before too.

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that modem is constantly flickering. if you put a router between your pc and modem you will see the internet light flicker quite often. I would put a router in if I were you.

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What modem do you have exactly? What is the model number?

Is your modem like this?

post-14624-1250026013_thumb.jpg

I always have something connected, ie my router -- but not sure if this light actually means traffic is being sent to the device on your lan side.. Or just activity the modem is seeing..

your always going to see traffic on the publc net -- always!! For starters just the arp traffic alone on a comcast network is crazy..

# tcpdump -ni dc0 arp

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode

listening on dc0, link-type EN10MB (Ethernet), capture size 96 bytes

16:35:34.420586 arp who-has 24.14.199.12 tell 24.14.198.1

16:35:34.446210 arp who-has 24.14.198.40 tell 24.14.198.1

16:35:34.484275 arp who-has 68.60.236.46 tell 68.60.236.1

16:35:34.484734 arp who-has 24.14.66.121 tell 24.14.66.1

16:35:34.525335 arp who-has 71.57.51.62 tell 71.57.50.1

16:35:34.717634 arp who-has 24.13.176.140 tell 24.13.176.1

16:35:34.720594 arp who-has 24.14.66.180 tell 24.14.66.1

16:35:34.896903 arp who-has 71.57.50.112 tell 71.57.50.1

16:35:35.005633 arp who-has 24.13.181.14 tell 24.13.176.1

<SNIPPED>

97 packets captured

417 packets received by filter

0 packets dropped by kernel

I counted to 5, so less than 5 seconds and 97 arps seen.. So yeah the lights going to flicker -- most interfaces will still be on even when the computer is off, etc.. Unplug the cable from the modem and see if the PC light stops.. But Im not really sure if its actual PC activity -- or just activity. Does not mean your PC is sending anything back -- can't be since its off ;)

But as suggested I would really suggest you put a router between you and the public net.

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I have both a Surfboard SB5120 and a SBG900 and on both the pc activity light is always flashing even though I'm not doing anything on the computer.

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It could also be that someone took control of your modem, injected new firmware into it and is using it as a proxy for something like a botnet.

Kinda far fetched, but possible... Try to see if there are any firmware upgrades for that modem, just to be on the safe side.

You've also said that you use torrents... That might also be the cause for the activity.

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To get back to the original question.

the PC activity light is just there to indicate that there is in fact a link between the modem and a PC/Router.

The reason that even when your PC is turned off the light is lit is that there is still power going to your PC and the NIC is still active, think "wake on LAN".

I can almost guarantee you that if you unplugged the power to your PC the light would go off withing 30 seconds.

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