understanding MAC address table entry for VLAN

SJ K · ‎05-12-2015

Hi all,

I have switch1 (fa0/5) connected to switch2 (fa0/1) using a trunk link. Both sides of the switch have the same VLANs

On Switch 1, when i issue show mac address-table, it is showing the interface of fa0/1 on switch2.

Vlan Mac Address Type Ports
---- ----------- -------- -----

   1    000a.41de.e601    DYNAMIC     Fa0/5
10    000a.41de.e601    DYNAMIC     Fa0/5
20    000a.41de.e601    DYNAMIC     Fa0/5
100    000a.41de.e601    DYNAMIC    Fa0/5

=======================================================================

I have a VLAN interface setup on switch 2 and i check its mac address but it is not the same as the above hence

I am wondering when would a packet / frame will be designated to switch 2 (fa0/1) and switch 1 need to check the mac address table to exit port fa0/5.

Please advise.

Regards,
Noob

Abhishek Soni · ‎05-12-2015

Hello Koh,

Kindly provide me 'show version', 'show interface vlan <>' and 'show mac address-table' from both the switch.

SJ K · ‎05-12-2015

Hi Soni,

S1>show version
Cisco Internetwork Operating System Software
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(22)EA4, RELEASE SOFTWARE(fc1)


S1#show interfaces vlan 100
Vlan100 is up, line protocol is up
  Hardware is CPU Interface, address is 0001.c7cd.92c1 (bia 0001.c7cd.92c1)
  Internet address is 192.168.10.1/24


S1#show mac address-table
          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----

   1    000a.41de.e601    DYNAMIC     Fa0/5
  10    000a.41de.e601    DYNAMIC     Fa0/5
  20    000a.41de.e601    DYNAMIC     Fa0/5
 100    000a.41de.e601    DYNAMIC     Fa0/5
 100    0040.0bc4.c801    DYNAMIC     Fa0/6

S2>show version
Cisco Internetwork Operating System Software
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(22)EA4, RELEASE SOFTWARE(fc1)


S2#show interface vlan 100
Vlan100 is up, line protocol is up
  Hardware is CPU Interface, address is 0001.636a.25d8 (bia 0001.636a.25d8)
  Internet address is 192.168.10.2/24


S2#show mac address-table
          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----

   1    000b.be60.1805    DYNAMIC     Fa0/1

Notice the mac address tables of each switch contain the opposite interfaces of the trunk setup between them. But what good use would it be in the mac address table ?

And i also realize although the VLANs are same on each switch, the mac address table isn't showing the same amount of entries.

Regards,
Noob

SJ K · ‎05-12-2015

Hi Soni,

Any update ?

Thanks!