Spanning Tree output

Unanswered Question
May 12th, 2009

Hi, What is the meaning of "Prio.Nbr" of Spanning tree output ? What "128.3 /128.18" says


Switch#sh spanning-tree vlan 130 brief


VLAN0130

Spanning tree enabled protocol ieee

Root ID Priority 8192

Address 000b.bf8c.a402

This bridge is the root

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


Bridge ID Priority 8192

Address 000b.bf8c.a402

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

Aging Time 300


Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Gi1/3 Desg FWD 4 128.3 P2p

Gi1/18 Desg FWD 4 128.18 P2p

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Paolo Bevilacqua Tue, 05/12/2009 - 20:46

Cost priority is self explaining.

Number is the unique port identifier for all ports on all bridges

--> Bridge id + port number



Rupesh Kashyap Tue, 05/12/2009 - 21:47

Thanks. One thing more, I am confused with Bridge ID. I know the Root ID. Please help me about Bridge ID.

skint Tue, 05/12/2009 - 22:24

BID is priority 8192 + extended ID (vlan 130) + MAC address.


In your case, you're the root, so the two lines of output are the same.

Rupesh Kashyap Wed, 05/20/2009 - 00:33

Hi, Why Interface No and Port ID is not matching in spanning-tree output ??



Interface Designated

Name Port ID Prio Cost Sts Cost Bridge ID Port ID

-------------------- ------- ---- ----- --- ----- -------------------- -------

FastEthernet0/9 128.10 128 19 FWD 19 32768 cc01.08e4.0000 128.10

FastEthernet0/10 128.11 128 19 FWD 19 32768 cc01.08e4.0000 128.11

FastEthernet0/13 128.14 128 19 FWD 0 32768 cc00.08e4.0000 128.14

FastEthernet0/14 128.15 128 19 BLK 0 32768 cc00.08e4.0000 128.15

FastEthernet0/15 128.16 128 19 BLK 0 32768 cc00.08e4.0000 128.16


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