Why some switch ports does not show mac address

[mahesh18]

                   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

[Leo Laohoo]

Most of the time, the MAC address does not show up when the clients have logged off.  This is very common nowadays with PCs.  Another is when a server's dual NIC isn't configured properly for "teaming".

If you don't know the exact IP address, there's an old trick (not foolproof) you could try.  IF you know what VLAN the NIC is in, ping the broadcast IP address from the switch.  Sometimes it just may work.

[mahesh18]

Hi leolaohoo,

The port is up up.

I know port is in voice and data vlan.

How can i find the broadcast IP for each vlan?

Thanks

MAhesh

[Leo Laohoo]

How can i find the broadcast IP for each vlan?

Please post the output to the command:  sh interface VLAN .

[mahesh18]

Hi leolaohoo,

Here is info

  Internet address is 192.168.20.1/24

Thanks

MAhesh

[Leo Laohoo]

  Internet address is 192.168.20.1/24

Your broadcast IP address is 192.168.20.255.  Ping that.

[mahesh18]

Hi leolaohoo,

If i ping to broadcast IP  my concern is that will this increase cpu spike as it is production device?

When i ping this IP it will send ping to all devices connected to this Vlan right?

also to other nei switches which are in data vlan right?

Thanks

Mahesh

[Leo Laohoo]

If i ping to broadcast IP  my concern is that will this increase cpu spike as it is production device?

Ping won't kill CPU.

When i ping this IP it will send ping to all devices connected to this Vlan right?
also to other nei switches which are in data vlan right?

If your switches are all in the same subnet, yes.

[mahesh18]

Hi Leolaohoo,

My bad the switch function as layer 2 it has static default route to core device.

Data vlan is on core switch.

IT has runk connection to core switch.

Thanks

MAhesh