3. Наблюдение поведения оборудования при изменении топологии

         На каждом из коммутаторов ( S1, S2 и S3)  включить режим отладки протокола STP командой debug spanning-tree events.

S1#debug spanning-tree events

Spanning Tree event debugging is on

S2#debug spanning-tree events

Spanning Tree event debugging is on

S3#debug spanning-tree events

Spanning Tree event debugging is on

         На корневом коммутаторе ( в данном примере S4 ) умышленно отключить один из trunk-портов

S4(config)#interface fa0/3

S4(config-if)#shutdown

S1#

*Mar 1 10:24:53.125: STP: VLAN1 Fa0/3 -> listening

*Mar 1 10:24:53.225: STP: VLAN1 Fa0/2 -> listening

*Mar 1 10:24:54.165: STP: VLAN1 heard root 32768-cc02.0ca0.0000 on Fa0/3

*Mar 1 10:24:54.169: current Root has 32768-cc00.0ca0.0000

*Mar 1 10:24:54.241: STP: VLAN1 heard root 32768-cc01.0ca0.0000 on Fa0/2

*Mar 1 10:24:54.245: current Root has 32768-cc00.0ca0.0000

*Mar 1 10:24:54.253: STP: VLAN1 Topology Change rcvd on Fa0/3

*Mar 1 10:24:54.257: STP: VLAN1 sent Topology Change Notice on Fa0/1

*Mar 1 10:24:54.293: STP: VLAN1 Topology Change rcvd on Fa0/2

*Mar 1 10:25:08.145: STP: VLAN1 Fa0/3 -> learning

*Mar 1 10:25:08.249: STP: VLAN1 Fa0/2 -> learning

*Mar 1 10:25:23.189: STP: VLAN1 sent Topology Change Notice on Fa0/1

*Mar 1 10:25:23.189: STP: VLAN1 Fa0/3 -> forwarding

*Mar 1 10:25:23.293: STP: VLAN1 sent Topology Change Notice on Fa0/1

*Mar 1 10:25:23.293: STP: VLAN1 Fa0/2 -> forwarding

S2#

*Mar 1 10:24:43.653: STP: VLAN1 Fa0/1 -> listening

*Mar 1 10:24:44.521: STP: VLAN1 we are the spanning tree root

*Mar 1 10:24:44.541: STP: VLAN1 heard root 32768-cc00.0ca0.0000 on Fa0/3

*Mar 1 10:24:44.545: current Root has 32768-cc02.0ca0.0000

*Mar 1 10:24:44.545: supersedes 32768-cc02.0ca0.0000

*Mar 1 10:24:44.549: STP: VLAN1 new root is 32768, cc00.0ca0.0000 on port Fa0/3, cost 38

*Mar 1 10:24:44.549: STP: VLAN1 sent Topology Change Notice on Fa0/3

*Mar 1 10:24:45.597: STP: VLAN1 Fa0/1 -> blocking

S3#

*Mar 1 10:24:24.921: STP: VLAN1 heard root 32768-cc02.0ca0.0000 on Fa0/2

*Mar 1 10:24:24.925: current Root has 32768-cc00.0ca0.0000

*Mar 1 10:24:24.973: STP: VLAN1 we are the spanning tree root

*Mar 1 10:24:25.097: STP: VLAN1 heard root 32768-cc00.0ca0.0000 on Fa0/1

*Mar 1 10:24:25.097: current Root has 32768-cc01.0ca0.0000

*Mar 1 10:24:25.097: supersedes 32768-cc01.0ca0.0000

*Mar 1 10:24:25.097: STP: VLAN1 new root is 32768, cc00.0ca0.0000 on port Fa0/1, cost 38

*Mar 1 10:24:25.097: STP: VLAN1 sent Topology Change Notice on Fa0/1