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Spanning-Tree Root Primary/Seconday

Spanning-tree vlan 1 root primary

Runs a macro and sets the priority lower than the current root, if the primary keyword is used and the current root bridge is more than 24,576 the local switch set it priority to 24,576.  Remember the default priority on all switches will be 32,768.

Example:

SW1#sh sp v 1

VLAN0001

Spanning tree enabled protocol ieee

Root ID    Priority    32769 priority (Default 32768 + Vlan1)

Address     000c.85aa.d6c0

Cost        19

Port        3 (FastEthernet0/2)

Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)

Address     001b.0c8d.3f80

Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type

—————- —- — ——— ——– ——————————–

Fa0/1            Desg FWD 19        128.2    P2p

Fa0/2            Root FWD 19        128.3    P2p

Fa0/7            Desg FWD 19        128.8    Edge P2p

spanning-tree vlan 1 root primary

VLAN0001

Spanning tree enabled protocol ieee

Root ID    Priority    24577 (priority 24576 + 1)

Address     001b.0c8d.3f80

This bridge is the root

Bridge ID  Priority    24577  (priority 24576 sys-id-ext 1)

Address     001b.0c8d.3f80

(spanning-tree vlan 1 priority 24576 is what is actually displayed in the running config)

 

 The secondary root bridge is used to set the bridge to a lower value of 28,672, again the default is 32,768

On SW2 if we run the secondary keyword

 spanning-tree vlan 1 root secondary

 vlan 1 bridge priority set to 28672 (Telling me what the new bridge priority)

VLAN0001

Spanning tree enabled protocol ieee

Root ID    Priority    24577

Address     001b.0c8d.3f80

Cost        19

Port        1 (FastEthernet0/1)

Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Bridge ID  Priority    28673  (priority 28672 sys-id-ext 1)

Address     000c.85b5.bb00

Just to recap spanning-tree vlan 1 root primary will set the root bridge to 24,576 + Vlan Number

The spanning vlan 1 root secondary will set the bridge priority to 28,672 + Vlan Number

 

 

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