Odd behaviour of modem?

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Rickles

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#207434 24-Dec-2016 18:15

My cable modem has the usual indicator lights, viz. power, DS, US, Online and Link. I've observed that the Link light blinks rapidly and a lot when on the internet per se, and assumed that this was an indication of data flow between the modem and my computer/s.

However, last night I noticed that the light kept on blinking even after turning off the PC. I even turned off wifi on the router to see what would happen, yet this Link light keeps flashing away.

Anyone tell me what, other than imminent arrival of the Mother Ship, or why this happens?

fe31nz

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#1694750 24-Dec-2016 23:26

Traffic LEDs normally blink for traffic from either direction. So if you have been doing something that has external connections coming into your PC (such as torrenting), then other computers will still be trying to connect to you and will be causing incoming traffic. That sort of traffic may continue for quite some time. Or maybe you have someone trying to hack into your home network - that will happen from time to time. Your ISP could also be accessing your modem to check its settings or update it.

Sometimes indicator LEDs are multipurpose, so they may flash fairly radomly for when something happens, but at other times (eg at startup or if a fault occurs) have a regular flash pattern that tells you some message.

Cable networks are often not point-to-point, but have shared traffic for everyone who is on your local cable. So there can be hundreds of connections on the same part of the cable network. The traffic is generally divided into three classes: broadcast, multicast and unicast. Unicast traffic has a specific destination IP address and your modem should only flash its LED when it sees traffic with your specific IP address(es). But broadcast traffic and a lot of multicast traffic has to be received by all the cable modems and then sorted out at a higher protocol level. So your modem may be flashing for all that traffic as well.

blakamin

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#1694760 25-Dec-2016 00:07

Cable modems never stop...

Hammerer

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#1694773 25-Dec-2016 00:24

I've noticed the same but my router is always on when the cable modem is on.

For my Cisco/Linksys DPC3008 the guides say the LINK LED only blinks with traffic:

http://www.linksys.com/us/support-article?articleNum=140792#f

http://www.cox.com/residential/support/internet/article.cox?articleId=004cee00-67a3-11e5-d061-000000000000

Rickles

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#1694852 25-Dec-2016 10:08

fe31nz - I understand all that, BUT no computers are turned on so no updates etc taking place, and I'd not expect the ISP to be polling that frequently?

blakamin - most logical answer

Hammerer - yep, that's the modem, and those links confirm supposed data flow.

BTW, the light goes out completely if I turn the router off, so it could be consistent attempts to connect to my computers/network but are hacks that endless?