Re: MAC Aging Time Behavior

Did not see anything in debug cdp events or debug cdp packet but have not tried an actual sniff yet!

Sent from my Verizon Wireless BlackBerry

Regards,

Joe Astorino
CCIE #24347

"He not busy being born is busy dying" - Dylan

-----Original Message-----
From: Carlos G Mendioroz <tron_at_huapi.ba.ar>
Date: Mon, 08 Aug 2011 21:07:20
To: Joe Astorino<joeastorino1982_at_gmail.com>
Cc: Cisco certification<ccielab_at_groupstudy.com>
Subject: Re: MAC Aging Time Behavior

I would look for any CDP message happening when PC port goes down.
May be some cisco black magic :)
(You will need a hub to test this, though. You still have one, right ? :)

-Carlos

Joe Astorino @ 08/08/2011 15:21 -0300 dixit:
> I am working on a port-security deployment and noticed something interesting
> to me. I was wondering if anybody else has seen this or can explain this
> particular situation. In this particular environment, we have IP phones
> directly connected to Cisco 3750-x access-layer ports. PCs are then plugged
> into the phones. I am using dynamic secure address learning with the below
> configuration:
>
> switchport port-security maximum 2
> switchport port-security maximum 1 vlan access
> switchport port-security maximum 1 vlan voice
> switchport port-security
> switchport port-security aging time 5
> switchport port-security aging type inactivity
>
> My original thought was to configure an aging time of 5 minutes of
> inactivity because aging is disabled by default (set to 0). The
> documentation seems to indicate that without setting an aging time,
> dynamically learned addresses will simply never age out. That all makes
> sense.
>
> Here is the interesting part to me -- If I unplug the PC from the downstream
> phone, the dynamically learned secure MAC address is immediately aged out on
> the switch. Also, the mac address is aged out of the mac address table
> immediately. I am wondering, how does this happen when the device being
> disconnected is downstream off another "switch". When I disconnect the PC
> from the switch port of the phone, does the phone in fact "signal" to the
> upstream switch somehow? If so, how does this happen? I can't find
> anything that explains that.
>
> One thought I had was STP TCN, but I am running RSTP on the switch and edge
> ports transitioning to down do not count as changes in RSTP. My only other
> thought is some sort of magic in CDP but I can't find anything that says
> that.
>
> Thanks guys for any feedback!
>
>

-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
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