stp problem

[Kashish_Patel]

I am seeing two different switches claiming themselves to be spaning tree root for the same vlan (using same mac address). Can anybody please explain how this is possible?

Switch1#sh spanning-tree vlan 192

Spanning tree instance for vlan 192

VL192

  Spanning tree enabled protocol rapid-pvst

  Root ID    Priority    32960

             Address     001c.7319.9d54

             This bridge is the root

  Bridge ID  Priority    32960  (priority 32768 sys-id-ext 192)

             Address     001c.7319.9d54

             Hello Time  2.000 sec  Max Age 20 sec  Forward Delay 15 sec

Switch2#sh spanning-tree vlan 192

Spanning tree instance for vlan 192

VL192

  Spanning tree enabled protocol rapid-pvst

  Root ID    Priority    32960

             Address     001c.7319.9d54

             This bridge is the root

  Bridge ID  Priority    32960  (priority 32768 sys-id-ext 192)

             Address     001c.7319.9d54

             Hello Time  2.000 sec  Max Age 20 sec  Forward Delay 15 sec

[benjammin]

This may be a silly question, but are the switches connected? Are they allowing the vlan to traverse the connection? Are you using VTP? What's the output of 'sh vtp status' of both switches?

[Rolf Fischer]

If all the switches use the default priority (0x8000 / 32768), the MAC-address is needed as the tie-breaker.

MAC-Adresses of course should be unique, otherwise with default configruration there is no tie-breaker and the bridges remain claiming themselves as rootbridges (no superior BPDU received).

Are that real switches or is it a simulation (packettracer, gns3)?

What about the other VLANs; do they also have the same MAC-Adresses?

Regards

Rolf

[milan.kulik]

Hi,

if you issue "show version" on the switches, do they both show the same Base ethernet MAC Address?

BR,

Milan

[Kashish_Patel]

They show different mac addresses.

001c.7319.9d54 is shown on switch1..switch2 shows different mac

[milan.kulik]

Hi,

how are the switches connected each to the other?

Aren't they in stack, e.g.?

BR,

Milan

[Kashish_Patel]

Switches are connected to each other, but they are not in stack.

I think it's because of mlag. thanks for your help!

[milan.kulik]

Oh, you are running MLAG there?

What kind of switches are those?

7600s?

BR,

Milan