show mac address-table question

[yong khang NG]

Hi,

When i issue the command of "show mac addreess-table int Gx/x/x", it return the outcome as below:

vlan   mac address     type   learn     age             ports

------+----------------+--------+-----+----------+--------------------------

*   20 d4ae.5290.07ef   dynamic Yes         25   Gi1/1/1

*   20 d4ae.5290.07ed   dynamic Yes         5   Gi1/1/1

My question:

Isn't that each interface should be able see ONE and ONLY ONE MAC address? But what's the explaination could happen this situation? Is it end point binding the server NIC as teaming NIC?

thanks

Noel

[sansarav720e]

Dear Noel ,

          let me know for following things ,

1) This switch port is connecting to another switch or to router ??/

2) This switch port is connecting to end machine or server ??

if its connected to another switch it ll learn multiple mac address along with it own interface mac address , if is connected to server which has got VMWare installed it will show different mac address for each VMWARE instance which has got different IP Address for each instance .

HTH

Thks

Santhosh Sarav

[Julio Carvajal]

Hello Yong,

If the switch is connected to a direct host ( no running any Virtual machine instance) then you should only see one but if the switchport is connecting to another devices that stores different MAC entries then you will see more than one MAC.

You can configure port-security in order to learn just one MAC address per interface ( again if you are connecting to another device that has an ARP table then you should no do this if you want to reach the devices that are connected to that box)

Regards,

Julio

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[sansarav720e]

Dear Yong ,

              Identify the port functionality , switch port-security applies only for the port which is connecting to end user machine , If you apply switch port security command on your uplink port which is connecting to another switch , it stop your entire network operation because it restrict MAC address only to one .

So please make sure while applying port security on your interface ..

HTH

Thks

Santhosh Sarav

[Eicke Friedrich]

today many end user machines (Intel, HP, Dell ...) have some kind of remote management (iLo, DRAC, Intel Management Engine ..) on board. Most of them don't have a dedicated network port so the are also connected through the system nic. So you often see two entries in mac address table. Often you can disable it through BIOS.

HTH

/Eicke

[Christian Bauer · Accepted solution]

Hello Noel,

according to the 2 consecutive MAC-Addresses which both belong to vendor "Dell" I also agree with Eicke -

It's really sure that your connected device (I assume that there is no further switch/hub/voice-phone with integrated switch/... connected) has a bulilt in management-board which doesn't use a second RJ-45 Jack.

So there are 2 devices "hidden" behind one NIC-Port. There is something like a mini-switch-circuit inside

your host - like it is IP-Phones where you are able to connect your PC to the VoIP-Phone.

And - a Switch is able to learn many many MACs on one Port.

Imagine the uplink-port of your switch. There comes the traffic from many other machines which are not

directly connected to your switch. Your switch will learn ALL Source-MACs from these devices over the uplinke port.

Greetings,

Christian

[yong khang NG]

thanks all for the feedback