[Insider Sharing] MAC address conflict into STP domain

Latest reply: Apr 28, 2014 02:55:46 3123 1 0 0

Hi,

 

Have you ever encounter a mac-address conflict into STP domain? What could be the reason for two systems to have the same mac?

Let’s consider we have a management vlan passing to all network elements inside the network and two of them  are using the same system-mac. Here we have 2 chassis of S7700 as below:

[Insider Sharing] MAC address conflict into STP domain-1238295-1

[SW1]display stp interface gi1/0/23

-------[CIST Global Info][Mode MSTP]-------

CIST Bridge         :4096 .aaaa-aaaa-aaaa

Config Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20

Active Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20

CIST Root/ERPC      :4096 .aaaa-aaaa-aaaa / 0 (This bridge is the root)

CIST RegRoot/IRPC   :4096 .aaaa-aaaa-aaaa / 0 (This bridge is the root)

CIST RootPortId     :0.0

BPDU-Protection     :Enabled

TC or TCN received  :26

TC count per hello  :0

STP Converge Mode   :Normal

Share region-configuration :Enabled

Time since last TC  :0 days 0h:4m:31s

Number of TC        :26

Last TC occurred    :GigabitEthernet1/0/23

 

[SW2]display stp interface G1/0/3

-------[CIST Global Info][Mode MSTP]-------

CIST Bridge         :8192 .aaaa-aaaa-aaaa

Config Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20

Active Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 19

CIST Root/ERPC      :4096 .aaaa-aaaa-aaaa / 0 (This bridge is the root)    

CIST RegRoot/IRPC   :4096 .aaaa-aaaa-aaaa / 20000 (This bridge is the root)

CIST RootPortId     :128.46 (GigabitEthernet1/0/3)

BPDU-Protection     :Enabled

TC or TCN received  :56

TC count per hello  :0

STP Converge Mode   :Normal

Share region-configuration :Enabled

Time since last TC  :0 days 0h:1m:31s

Number of TC        :52

Last TC occurred    :GigabitEthernet1/0/3


According to the output, both switches consider themselves root-bridge for stp domain. Because of this anomaly,  layer 2 network is not stable, TC packets are flooded continuously inside stp domain. Check the number of TC packets and occurrence timer.

 

But, what could be the reason for duplicate mac-address? I think I can explain why this phenomenon appears on chassis.

 

By default, a switch uses the MAC address of the master MPU on the local chassis as system-mac, and the slave MPU and LPUs also use the MAC address of the master MPU. After the Slave MPU of  a switch (SW1) is installed on another switch (SW2), it still uses the original MAC address. If the other MPU and LPUs use this MAC address, a MAC address conflict occurs.

 

Identify the fault: run the display system-mac command to check the MAC address of switch SW1. If the default MAC address and current MAC address displayed in the command output are different, the switch does not use the default MAC address of the newly installed MPU and a MAC address conflict has occurred.

 

Rectify the fault: run the restore system-mac command in the diagnosis view to restore the MAC address of the device to the default MAC address of the newly installed MPU. You will need to reboot the system in order to take effect.

 

<SW2>sys

Enter system view, return user view with Ctrl+Z.

[SW2]diagnose

Enter diagnosis view, return user view with Ctrl+Z.

Info: The diagnosis view is used to debug system hardware and software. Misuse of certain commands in this view may affect system performance. Therefore, use these commands with the guidance of Huawei engineers.

[SW2-diagnose]restore system-mac

[SW2-diagnose]

Info: The master current mac and default mac are the same, will not change it.

The slave public mac-address restore pass!

Info: System-mac has been changed, need reboot to take effect.

 

You also have the possibility to change the current MAC with default MAC manually:

 

[SW2-diagnose]set system-mac ?

  current  Current mac

  default  Default mac


 and reboot.

Do not change the current system-mac to a random one, because it might result another mac-address conflict. I recommend to keep default system mac-address as current system-mac. 

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Sophoni
Created Apr 28, 2014 02:55:46 Helpful(0) Helpful(0)

Good!
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