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STP Loop

Unanswered Question
leonvd79 Tue, 02/28/2006 - 03:28
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show spanning-tree vlan x detail


See where the Topology Change was sourced from. Also check to see when and how many TC occured.


HTH


Leon


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leonvd79 Tue, 02/28/2006 - 04:13
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View the output of the command "show spanning-tree vlan 1 detail" for instance.


It would tell you how much time has elapsed since the last topology change. Did it happen five minutes ago, or three hours.


How much times did it occur, 10 or 8390? Based upon these values you can see if there was a loop and how often it would've occur.


Martin,


Choosing between Rapid Per-VLAN STP or Per-VLAN STP should be based on application requirements. If your application requires fast convergence it is recomended to use Rapid Per-VLAN STP.


I assume the GREEN non-Cisco switches do not support Rapid STP (802.1W) nor Multiple STP (802.1S), which would mean that you'd have a mixed 802.1d and 802.1W environment. This is not recomended.


Since the GREEN switched are single-homed, it would be appropiate to disable STP. The switchport on Catalyst 2950 can auto-detect the STP port-type. Make shure that no BDPUs are received on edge-ports by entering the "spanning-tree bpdu-guard default" command in global configuration.


Portfast, Uplinkfast and Backbonefast are Cisco proprietary enhancements to 802.1d. Which are re-used in Rapid STP, as defined by IEEE 802.1W. These features were designed to speed up reconvergence.


Since a fast reconvergence is dictated by business requirements 802.1W is increasingly popular to meet those recomands in building a robust network.


To answer question 2, I uplinkfast detects indirect link failures, in this case you would enable a switchport which is put into blocking because the rootpath is not shorter than the current.


HTH


Leon


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