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Possible bottleneck : Switch becomes overwhelmed with broadcasts

Once in a while, some of my users loose connection to the network. I don't see anything in eventvwr (NT 4) on my servers. I'm not using network monitor because it takes up to much juice out of those old servers. One thing strange I notice last it hapens is that all the Packect lights on the 3Com SuperStack III switch. Correct me if I'm wrong, but usually, when it flashes on every port, it means that it is a broadcast. But when the users are disconnected from the network... that switch keeps flashing on the broadcast port for a couple of minutes. Then it goes back to normal and users can have access to the network.

Is this a bottleneck problem?
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8mathieu8
Asked:
8mathieu8
1 Solution
 
map000Commented:
check firmware updates first
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Chris DentPowerShell DeveloperCommented:

And you might want to check on the source of the broadcasts.

To do that I recommend picking up a copy of Ethereal (www.ethereal.com) which is a free (open source) packet sniffer. It's an excellent little program and if you load it up it will let you see any traffic (source, destination, port, protocol etc etc) that your computer can see.

If, during the network outage, you see an abnormal amount of traffic from one particular network device it might be more worthwhile trying to resolve that than concentrating on the switches alone.
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8mathieu8Author Commented:
Ok, I'll try ethereal...but again, that problem occurs about once a week. I can't keep that sniffer running all the time! .... unless I set up a computer only for that! Does it take alots of space on the hard drive? I supose that I'll have to put the NIC in promicuous mode. But againt, wouldn't that only capture packects that are broadcasted since this is a switch and not a hub?
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Chris DentPowerShell DeveloperCommented:

Since it's Broadcast you want to catch (or that may be causing the problem) you don't need Promiscuous mode. And besides, as you quite rightly point out, switches don't even forward all traffic through all ports (unless of course you have a switch capable of doing that).

Personally I'd run it on a something that isn't doing much or anything else.

Any reason you can't you keep the sniffer running that long? Almost no processer usage required, barely any hard disk usage etc etc.

Setting it to Log to a file will allow you to track back to whenever there was a problem if needed so you wouldn't have to watch it all the time (of course you would need to allow space for the file) and I'd recommend flushing the log every couple of days just to give you less to search through.
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8mathieu8Author Commented:
Your right, I don't need promiscuous mode since its a broadcast! ;)
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gjohnson99Commented:
Another to find it is to unplug stuff till it go away.

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8mathieu8Author Commented:
I give Chris-Dent the points. Even if I didn't try is recommendation, I find that it is the best thing to try.
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