Determine the Root Bridge in an MSTP-Fabric Connect Multi Homing Configuration

Identify the root bridge by determining where the Common and Internal Spanning Tree (CIST) regional root MAC address is learned for the STP-reserved I-SID. Check which MAC address has the same first five octets as the CIST regional root MAC address.

About this task

When you enable MSTP-Fabric Connect Multi Homing, you can use the following two commands to determine which BEB is the root bridge:

show spanning-tree mstp status
show i-sid mac-address-entry 16777003

Procedure

To enter User EXEC mode, log on to the switch.
Determine the CIST regional root:

show spanning-tree mstp status
Determine which MAC address has the same first five octets as seen in the CIST regional root MAC address:

show i-sid mac-address-entry 16777003

Example

In the following example, bold text identifies the relevant information in the command output. In the output of the second command, the DEST-MAC shows 10:cd:ae:6e:d8:84, which is the system ID of the CIST regional root BEB, and the system name is BEB-1000.

Switch:1>show spanning-tree mstp status

==========================================================================================
                                  MSTP Status
==========================================================================================
------------------------------------------------------------------------------------------
Bridge Address                : b0:ad:aa:4d:b8:00
Cist Root                     : 80:00:10:cd:ae:6e:d8:00
Cist Regional Root            : 80:00:10:cd:ae:6e:d8:00
Cist Root Port                : fabric
Cist Root Cost                : 0
Cist Regional Root Cost       : 2000000
Cist Instance Vlan Mapped     : 1-1024
Cist Instance Vlan Mapped2k   : 1025-2048
Cist Instance Vlan Mapped3k   : 2049-3072
Cist Instance Vlan Mapped4k   : 3073-4050,4053-4059
Cist Max Age                  : 20 seconds
Cist Forward Delay            : 15 seconds

Switch:1>show i-sid mac-address-entry 16777003
===========================================================================================================================================
                                               I-SID Fdb Table
===========================================================================================================================================
I-SID     STATUS  MAC-ADDRESS        INTERFACE        TYPE       DEST-MAC           BVLAN DEST-SYSNAME           AREA-ROLE     AREA-NAME
-------------------------------------------------------------------------------------------------------------------------------------------
16777003  learned 10:cd:ae:6e:d8:82  Port-1/9        NON-LOCAL  10:cd:ae:6e:d8:84  4051  BEB-1000               HOME          area-20.0020                   
16777003  learned 10:cd:ae:db:a4:83  Port-1/40        NON-LOCAL  10:cd:ae:db:a4:84  4051  7208                   HOME          area-20.0020
16777003  learned b0:ad:aa:40:14:82  Port-1/40        NON-LOCAL  b0:ad:aa:40:14:84  4051  6222                   REMOTE        area-20.0020