[CentOS] OT - odd behavior of Cisco switch

[m.roth at 5-cent.us]

Les Mikesell wrote:
> On Thu, Feb 7, 2013 at 1:52 PM,  <m.roth at 5-cent.us> wrote:
>> >>>
>>>> Btw, we are on our own VLAN. The switch is on it.
>>>
>>> Is the traffic in question to something directly connected to this
>>> switch and just appearing mirrored to the wrong port or perhaps
>>> broadcast to all of them?   Or is the actual destination on some other
>>> switch where this one shouldn't even be in the path?   If you want to
>>> track the problem down you need to look backwards from the target and
>>> figure out why the switches in between did not learn the correct path.
>>>  It is not likely to be related to the traffic bandwidth unless some
>>> intermediate link is flooded to the point that nothing works.
>>
>> Let's try ASCII art:
>> (campus net)->[vlan]->[new switch in rm. 1]-> server 1
>>                     \                      -> server 3
>>                      \->[switch in rm. 2]->server 2
>>
>> And he was seeing traffic between 1 and 2 on 3. And he tried another
>> server in rm. 1, and saw it.
>>
>> Does that make it clearer?
>
> Do you have a huge number of machines on this network?  The switches
> have to store the whole table of all MACs on each side for the ports
> and a 3750 should default to default to somewhere between 3K and 12K
> depending on the configuration.    A 'show mac address-table count' on
> the switch should show the number of active entries and the available
> space.  I've never had to fiddle with that, but there should be
> commands to tune the size and aging times.

No, not huge numbers. The old switch they replaced was a 48 port, of which
*maybe* 2-3 were empty. The new -they've got two of them cabled together
(and there is much rejoicing). I don't believe *we* can get on their
managed switch. *sigh*

      mark