[CentOS] OT - odd behavior of Cisco switch

[Les Mikesell]

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.

-- 
   Les Mikesell
     lesmikesell at gmail.com