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New Member

unicast storm control query on 3550


I've implemented storm control across a number of 3550s with no issue. The config for all switchports is:

storm-control broadcast level 1.00

storm-control multicast level 5.00

storm-control unicast level 5.00

A node plugged into a 3550 port stopped responding to tcp requests today. Investigations show that storm control has moved the port into a blocking stats because unicast is utilising 100% on that port.

If I set the switchport to storm-control unicast level 100.00 it starts responding again, but I'm not happy about leaving it in this state without fully understanding the repercussions.

Excessive broadcast traffic I can understand - but can anyone explain how a unicast 'storm' is defined, as generally the majority of traffic is going to be unicast anyway.

I am seeing a small amount of broadcast traffic in addition to the unicast traffic - about the levels I would expect, so its not a case of 100% of the traffic being unicast and 0% being broadcast...

Can anyone clear these muddy waters for me?

New Member

Re: unicast storm control query on 3550

Having investigated this further, the problem is 'unknown' unicast traffic rather than unicast traffic to known addresses.

The problem in this instance would appear to be that the node generating the traffic is compromised, this confused diagnosis because the tcpdump binary I was using to sniff network traffic was compromised so the traffic I was interested in seeing was being excluded.

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