stp enable

Unanswered Question
Jun 12th, 2007

i attched network diagram. i want to enable stp. pl. help

I have this problem too.
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royalblues Tue, 06/12/2007 - 09:13


STP is enabled by default in the switches. you can just manipulate the way STP operates and selects forwarding ports.

seeing your topology, it would be best to keep the 3750 switch as the root switch

Issue the following command to force it to operate as the root for vlans 1 - 40

"spanning tree vlan 1 - 40 root primary"

Also on each access switch enable uplinkfast for faster convergence

in the global configuration mode type

"spanning-tree uplinkfast"

HTH, rate if it does


upendra07 Tue, 06/12/2007 - 22:22



we have vlan range 67-90.As per your suggestion i will run the following command l3

"spanning tree vlan 67-90 root primary"

It's ok.

"spanning tree uplinkfast" this command only for the l2. am i right?

royalblues Tue, 06/12/2007 - 22:31

yes you are correct.

spanning tree vlan 67-90 root primary would make it the root for the vlans 67-90.

When you add any new VLANS later, then you can again issue the command spanning-tree vlan root so it make it the root for that vlan

HTH, rate if it does


upendra07 Wed, 06/13/2007 - 03:58

I tried but i am facing problem when l3 direct link connect to l2 goes down other path was not active.

royalblues Wed, 06/13/2007 - 04:08


what do you see when you do sh spanning-tree vlan 67 on the access switches.

If you have uplinkfast enabled, then you should see one port as FWD and the other as ALT-BLK.


royalblues Thu, 06/14/2007 - 05:38


on the L2 switch

you should see something like this. Here Gi1/2 is shown as ALT/BLK which will go into forwarding state in 5 sec when the root port fails.

MS_TRG_WINGA_SW1#sh spanning-tree vlan 2


Spanning tree enabled protocol ieee

Root ID Priority 49154

Address 001a.e3b4.1d80

Cost 3004

Port 1 (GigabitEthernet1/1)

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

Bridge ID Priority 49154 (priority 49152 sys-id-ext 2)

Address 001b.0cee.3180

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

Aging Time 300

Uplinkfast enabled

Interface Role Sts Cost Prio.Nbr Type

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

Gi1/1 Root FWD 3004 128.1 P2p

Gi1/2 Altn BLK 3004 128.2 P2p

Fa2/2 Desg FWD 3019 128.66 P2p

Fa2/3 Desg FWD 3019 128.67 P2p

Fa2/4 Desg FWD 3019 128.68 P2p

Fa2/5 Desg FWD 3019 128.69 P2p

HTH, rate if it does



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