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At work, we have a basic Class C Network. The gateway/router is a SMC8013WG (stock comcast commercial cable modem), and simple unmanaged switch (HP Pro Curve 1400 24G).

The SMC8013WG is our default gateway as well as DHCP server.

Periodically, I'd say almost every other day.. the entire network will just stop responding. I won't be able to ping/see the gateway, any computers on our local network, or anything on the internet.

The only way to fix this is to unplug the Comcast cable modem, wait, and plug back in. This unfailingly fixes the problem.

But this doesn't make much sense to me.. shouldn't the network still be fine locally, since everything is plugged into the switch anyway? Why would resetting the router fix this?

Can anyone suggest anything to check to in order to narrow this problem down?

Just to be clear.. here is the basic topology:

{ Internet } -- (12.345.67.89) Comcast Cable Modem (192.168.1.1) -- Switch -- 192.168.1.2-254

P.S. Our IT guy is in about 3 hours a day every other week or so, so.. we're kind of on our own most of the time.

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3 Answers 3

up vote 1 down vote accepted

Could be something is flooding the network from a malfunctioning router. It's possible that you could see something with a sniffer, or you might be able to see something on the switch with the activity lights, possibly. But it sounds like something is completely wonked with the router. Since just restarting the router fixes the issue it's unlikely at this point to blame the switch.

It's hard to tell how the router is screwing up your network...it would be pure speculation, but it could be doing something that is killing the switch, especially since it's a lower end switch in terms of debugging options.

I'd call Comcast, describe the symptoms, and ask for a new router to be sent to you.

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Yea, heh, we did that today. I spent about 5 minutes trying to explain to the guy that our router does in fact have something to do with local networking problems, but he seemed content to continually repeat that the WAN signal seemed find. >.> –  mkocubinski Jan 4 '11 at 1:42
    
Yeah, they'll do that. Sometimes you just have to be persistent until they'll put the @#% script away and fix the problem...or convince them that it's cheaper to just give you another $50 router to get you off the line instead of tying up $100+ worth of their time. –  Bart Silverstrim Jan 4 '11 at 3:04
    
I've seen a Cisco switch once with some sort of memory issue corrupt the arp tables in other switches on the network cause strange issues like this. But it's very difficult to diagnose these issues without managed switches. –  3dinfluence Jan 4 '11 at 4:24

This router is in the End of Life list from Comcast, and it should be replaced by Comcast. You can check this at http://mydeviceinfo.comcast.net/

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I agree with what Bart said.

But as a shot in the dark the SMC routers for Comcast Business have some known issues associated with it's "smart packet detection" which typically presents itself as problems with routing traffic to a single url or IP on the Internet. However I don't think that feature does anything on the LAN, hence the shot in the dark, but if it were to target dhcp, dns, or broadcasts traffic on the LAN ports it could present itself in symptoms that you're describing. Over all that feature seems to cause more problems than it solves. So I would disable it. It's enabled by default and you have to check a checkbox to disable it. This option is found in the Firewall options on that router. If this doesn't clear up your issue you you can always change this setting back but like I said it's known to cause more issues than it solves.

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