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Disabling Spanning Tree !?

Hi, Have a client with 2 x 6500/720 Collapsed Core Dsitribution and 60+ legacy access switches. The legacy access switches provide a loop free topology (normally!)and the client is keen to disable Spanning Tree. I'm not happy with this and would prefer spanning tree enabled even in the absence of a looped topology. What are your views, is the Cisco recommendation to always enable STP?


Re: Disabling Spanning Tree !?


If u dnot have any redundant links then u can go with disabling STP.But it is better to have it enabled.




Re: Disabling Spanning Tree !?

Hello Les,

Yes Cisco recommends to enable spanning tree under all circumstances.

Cisco switches run Per-VLAN Spanning Tree by default. In case of a large amount of VLANs (up to 128 supported) this can affect CPU performance.

If the legacy switches don't run 802.1d you can disable spanning-tree on a per port basis.

At least you can keep Spanning Tree in the core, since it is most likely to see redundant paths between your C6500's.



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Re: Disabling Spanning Tree !?

Not running spanning tree at all is asking for it. If every port was a routed port including all the edge ones then I would do it.

Even if you configure everthing perfectly some stupid user will get you. All they need to do is plug a cross cable between 2 ports and that vlan is gone. HP switches and many consumer ones will now auto negotiate the straight/cross cable. So users can loop your network with straight cable.

Re: Disabling Spanning Tree !?

If there is no redundancy in the network, you can have them enable portfast everywhere. A simple global command, spanning-tree portfast default, allows you to do that (well, it will still have to be manually configured on trunks). This way, you will keep the simple behavior and immediate convergence speed of a network without spanning-tree, while keeping spanning-tree in case of a configuration error (bad cabling etc...). If the number of vlans is an issue (cat6k supports thousands of vlans even in PVST mode, check the release notes), you can simply switch to MST mode. Again, if there is no redundancy in the network, there is no need for any STP configuration.

If they really don't want STP after that, it's purely for religious reasons... Some people are convinced STP creates bridging loops, maybe it's not a bad idea to let them disable it and check by themselves;-)



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Re: Disabling Spanning Tree !?

Thanks for all the replies. For clarity I should have said that the legacy access switches are non Cisco with dual uplinks from either single access or dual access switches. They support a L2 link failover feature that does not rely on spanning tree. My concern is if that feature fails or a patching error occurs then spanning tree saves the day. There are approx 100 vlans so no problem with pvst mode.

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