05-23-2012 09:08 AM - edited 03-07-2019 06:51 AM
Hi all,
I was finding out which device is connected to switch port.
I did this command to find mac address
sh mac address-table int gigabitEthernet 2/23
Multicast Entries
vlan mac address type ports
-------+---------------+-------+--------------------------------------------
225 ffff.ffff.ffff system Gi2/1,Gi2/2,Gi2/4,Gi2/5,Gi2/6,Gi2/7,Gi2/8
Gi2/9,Gi2/10,Gi2/11,Gi2/12,Gi2/13,Gi2/14
Gi4/39,Gi4/43,Gi4/48,Po25
625 ffff.ffff.ffff system Gi2/1,Gi2/2,Gi2/5,Gi2/6,Gi2/7,Gi2/8,Gi2/9
Gi2/10,Gi2/11,Gi2/12,Gi2/14,Gi2/15,Gi2/16
Gi4/48,Po25
seems ffff is all broadcast address .
Need to know why this is not showing mac address thanks
MAhesh
Solved! Go to Solution.
05-23-2012 02:33 PM
Hello Mahesh,
L2 information for the port looks like fine.
To learn a MAC address on the port the attached device has to speak and to be understood by the switch port.
So a first possible case is given by some incompatibility between more modern C4500 linecards (I remember a case with WS-4648 on new C4500 that required upgrade of network drivers on PC NICs)
Another possible situation is given by wake on lan the connected device is powered but it does not show activity so no MAC is learned on the port.
CAM aging time is by default only 300 seconds so another case is a device like a PC that is powered on, connected but it hasn't used the LAN for more then 300 seconds so its entry has expired and it has been removed from CAM table
Hope to help
Giuseppe
05-23-2012 09:47 AM
Hi Mahesh,
What are the switch model and IOS version?
Kind Regards,
Ivan
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05-23-2012 10:28 AM
Hi Ivan
cisco WS-C4506 and
bootflash:cat4500-ipbasek9-mz.122-54.SG.bin"
Thanks
05-23-2012 11:05 AM
Hi Mahesh,
Check if you have broadcast storm in the network. Also verify for STP transitions:
show span int gi2/23 //check for topology changes
I saw similar issue related to static mac configuration. Do you have any of that in the config?
Kind Regards,
Ivan
**Please grade this post if you find it useful.
05-23-2012 11:30 AM
Hi,
Here is info
sh spanning-tree int gi2/23
Vlan Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0225 Desg FWD 3100 128.87 P2p Edge
VLAN0625 Desg FWD 3100 128.87 P2p Edge
I chekced no static mac on switch port config.
thanks
mahesh
05-23-2012 02:33 PM
Hello Mahesh,
L2 information for the port looks like fine.
To learn a MAC address on the port the attached device has to speak and to be understood by the switch port.
So a first possible case is given by some incompatibility between more modern C4500 linecards (I remember a case with WS-4648 on new C4500 that required upgrade of network drivers on PC NICs)
Another possible situation is given by wake on lan the connected device is powered but it does not show activity so no MAC is learned on the port.
CAM aging time is by default only 300 seconds so another case is a device like a PC that is powered on, connected but it hasn't used the LAN for more then 300 seconds so its entry has expired and it has been removed from CAM table
Hope to help
Giuseppe
05-24-2012 07:59 PM
Hi Giuseppe,
Thanks again seems its some wake on lan setup on main switch.
Regards
MAhesh
10-05-2017 06:44 PM
Hello! can you pls elaborate on this "So a first possible case is given by some incompatibility between more modern C4500 linecards (I remember a case with WS-4648 on new C4500 that required upgrade of network drivers on PC NICs)"
how did you figure out that it was an incompatibility? I'm just working through some issues with devices on a newly installed 4500. Any info would be appreciated
05-23-2012 11:53 AM
"Why some switch ports does not show mac address"
Because those port in question in a vlan, for which have layer2 definition yet to be created.
meaning you assigned a port to a vlan but you have not created a layer2 defenition.
Hope that answers your question.
thanks
05-23-2012 11:59 AM
Hi,
Thanks for reply.
I check port config it is assigned to Voice and data vlan.
Can you please explain below
meaning you assigned a port to a vlan but you have not created a layer2 defenition.
thanks
MAhesh
05-23-2012 02:41 PM
Mahesh,
In addition to the options provided by Giuseppe (Hi Giuseppe, long time no see) try pinging the device and than issue the sh mac address-table command.
This usually does not apply to PC, Laptop, etc.... but I have seen some video camera encoders that the MAC address does not show up on the switch unless you ping it first. Strange right?
HTH
05-23-2012 03:52 PM
Hi Reza,
Sh ip arp does not work also i do not know IP address of device.
Thanks
MAhesh
05-23-2012 04:01 PM
Hi Mahesh,
Try clearing the MAC table:
clear mac address-table dynamic interface gi2/23
and than try "sh mac address-table again
HTH
10-29-2018 03:57 AM
Nice tip that Reza
07-25-2014 05:52 AM
This really helped me, thanks! I had trouble with a similar device.
The switch didn't cached the mac address of the device. So I just pinged the device :)
I think you could ping to the broadcast if you don't know the exact address.
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