[CentOS] OT - odd behavior of Cisco switch

[SilverTip257]

On Wed, Feb 6, 2013 at 11:01 AM, <m.roth at 5-cent.us> wrote:

> Ww just had our switch replaced with a pair of 3750G's, old and new all
> have 48 ports, so we now have some open ports.... Anyway, my manager was
> looking at issues yesterday, and discovered that for a while, off and on,
> from several systems on the new switches, he could see traffic between
> *other* servers and systems elsewhere in the building... which, of course,
> shouldn't be possible with a switch.
>
> He tells me that some switches, if they were overwhelmed with traffic,
> would give up and go into hub mode, but he's under the impression that was
> written out of the firmware years ago, while these are new switches.
>

I suppose anything is possible, but I've never heard or seen that happen
first hand.

If one of your hosts intermittently loses connectivity, the switch will
broadcast that traffic to all ports because it can't find the host's MAC
address.

(And what Les said about the switch broadcasting traffic until it learns
MAC addresses.)

Last week we had a co-located customer participating in a DOS attack and we
made the mistake of shutting off the port he was on.  Wouldn't you know it
that the inbound traffic was broadcast out all operational ports on that
switch because the switch couldn't locate the host. That didn't seem to
cause any problems, but it did make the switch port graphs pretty. ;)


>
> Anyone run into this?
>
>      mark
>
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-- 
---~~.~~---
Mike
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