Spanning Tree Basics

Unanswered Question
Feb 29th, 2008

For a basic Spanning-Tree setup is this a good starter...

Designated root bridge commands;

spanning-tree mode pvst

spanning-tree vlan xx priority 4096

And all other (non-root) bridges commands;

spanning-tree mode pvst

spanning-tree extend system-id

I know other things like UDLD and BPDU Guard are useful, but for a basic mesh setup are the above commands enough to be going on with and avoid Loops?

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Overall Rating: 5 (1 ratings)
Jon Marshall Fri, 02/29/2008 - 03:38

Hi Mike

I generally do the following.

1) Select 2 switches to be spanning tree root primary and spanning tree root secondary.

2) On primary root -

spanning-tree vlan xx priority 8192

3) On secondary root

spanning-tree vlan xx priority 16384 - where vlan xx is the same vlan number as in 2).

If all your switches support Rapid-pvst I would run this instead of pvst.

If you use the extended system-id use it on all the switches including the root and secondary.



Edison Ortiz Fri, 02/29/2008 - 06:33

The system-id, along with the switch priority, and the allocated spanning-tree MAC address, enables to make the bridge ID unique for each Vlan in order to avoid a tie between 2 switches when electing the root for a Vlan.

For instance, if you configure a switch as a root for a Vlan and another switch as a root for the same Vlan, the switch with the lower MAC address will win the election process due to its system-id information.





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