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Spanning-tree time to establish a new path to the root bridge

Posted on 2014-02-24
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Last Modified: 2014-02-25
I have connected a Cisco 4500 series switch to a Cisco 6509 (allow all vlans), the switch all ready had a connection to another switch Cisco 3750 (allow all vlans). Spanning tree has blocked the connection to the Cisco 6509. I want to shut down the trunk ports going from the 4500 to the 3750 so the 4500 traffic will all go through the Cisco 6509 (root bridge). All devices have been taken off of the 3750 and placed on the 4500 so traffic is going from the 4500 through the 3750 out to the router and to the external network. I'm wanting to know how long it will take for spanning tree to unblock the ports on the 4500 going to the 6509 after I shutdown the ports on on the 4500 going to the 3750.

Thank you,
D
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Question by:dsterling
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unfragmented earned 500 total points
ID: 39884727
For original STP (PVST), its in the region of 30 secs (15 secs listening + 15 secs learning).

For 802.1w "Rapid" STP (PVRST), its fast - normally under a second.
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by:rauenpc
ID: 39885773
Instead of shutting down the trunk, I would think this would be best solved by configuring spanning tree to direct traffic at the 6509. This might easily be resolved by just changing the priority on the 6509. This way, all three switches can stay connected, and traffic will go the direction you want it to.

This may or may not be the answer, but to change the priority for all vlans on the 6509 (assuming you are running stp, pvst, or rapid-pvst)

spanning-tree vlan 1-4094 root primary
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by:Soulja
ID: 39885881
Proper design would be to never use your access layer as a transit path for spanning-tree/layer 2 traffic. I would not even connect the 3750 or the 4500 together, unless for some reason you will be using one of these switches as a root bridge for a specific vlan. If all of your vlans are root primary on the 6509, I would just run a port channel from the 3750 to the 6509, and run a port channel from the 4500 to the 6509. Thus, you will have not ports blocked and not loop to worry about.
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by:dsterling
ID: 39885957
This is what I was looking for, thanks
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