Spanning tree configuration for Cisco switches

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• Configure layer 3 switches as STP root

  Go to global configuration mode and use 'spanning-tree vlan <vlan_id> root primary'. Do this only for VLANs created in that switch (That is VLANs shown when you use 'show run')

• Configure user ports on 2912-2924 switch with portfast and bpdufilter

  Use following commands for each interface

  'spanning-tree portfast'

  'spanning-tree bpdufilter enable'

• Configure user ports on 2950+ switches with portfast, bpdufilter and bpduguard

  'spanning-tree portfast'

  'spanning-tree bpdufilter enable'

  'spanning-tree bpduguard enable'

• Configure 2950+ switches to automatically recover from bpduguard after some fixed interval. That is, in global configuration mode use

  'errdisable detect cause bpduguard'

  'errdisable recovery interval 300'

  (Note: By default settings are same as being configured by above lines. Hence above lines will not appear in 'show run')

Note: Here by user ports we mean all ports in access mode.

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