How to configure STP on Cisco 3750 Switches.

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Jul 21st, 2010
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Hi All

I have 10 cisco Switch 3750 in LAN. All these are in connected in Ring. All those are configured with multiple VLAN's and Routing is also enable. I want to enable STP on all these switches. In case if any links drop between two switches and auto backup from other side.

I would apperciate if anyone can help.


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Overall Rating: 4.7 (3 ratings)
mkumailali Wed, 07/21/2010 - 05:45
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Thanx for reply,

yeah this is right, By default this is enable on cisco Swiches 3750.

I want to make one switch as a Root Switch and others as client.

so does i need to configure only my Root Switch for STP or i will enable on all switches.

By default STP will choose one switch as root bridge.

Any switch you want elected as root bridge for all vlan do the below configuration on it

sw 1 (config) #spanning-tree vlan (vlans id e.x:1,3-5) root primary

if you if this switch go down and you don’t want STP calculate and choose any switch

you can go to second switch and use :

sw 1 (config) #spanning-tree vlan (vlans id e.x:1,3-5) root secondary

mkumailali Wed, 07/21/2010 - 06:32
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It mean i need just  configure only root Switch and did disable STP on other switches ?

bonnardopjl Tue, 07/27/2010 - 02:50
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Please note that STP is limited to 7 successives links.

So in your case (10 swoiches in ring), I am afraid the topology could

not be computed in case of failure of one link.

CSCO11584685 Tue, 07/27/2010 - 03:41
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I Agree with that. It is known that STP start making issues once the ring goes beyond 6 or 7 switches.

If your Vlans are all local to one switch (ex. sw 1 has vlan 20,30. sw 2 has vlan 40,50). then i would recommend to change the connecting links to routed ports and just do proper routing between. the routing protocols will take care of loops/convergence in case of link failures.

mkumailali Tue, 07/27/2010 - 07:28
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All the core(3750) switch are connected on trunk and Distribution(3500/2950) switch are also connected on trunk with core switch(3750), then on Distribution switch  (3500/2950) srw/Netgare are connected through VLAN


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