Eaddy
As a CCNP choice and a CCNA, perhaps you are tempted to skip or just browse the many details of Spanning Tree Protocol. After all, you learned all of this in your CCNA reports, right? That is right, but it never hurts to review STP for a changing exam! Besides, many of us consider the four STP port states - but basically, there's a sixth one!
Disabled is not generally speaking looked at as an STP interface state, but Cisco does technically consider this to be an STP state. A port is the one that is administratively shut down. read this
When the port is opened, the port will go in to blocking state. As the name suggests, the interface can't do much in this state - no frame forwarding, no frame getting, and therefore no learning of MAC addresses. In regards to the only thing this interface may do is recognize BPDUs from nearby switches.
A slot will likely then go from blocking mode into listening mode. The most obvious problem is "listening for what?" Listening for BPDUs - and this interface can now send BPDUs as well. The port still can't forward or receive data frames.
Once the interface goes from listening mode to learning mode, it is getting ready to send and receive frames. In understanding mode, the interface begins to understand MAC addresses in preparation for putting them to its MAC address dining table.
Eventually, an interface can enter forwarding mode. A port is allowed by this to forward and receive information frames, send and receive BPDUs, and place MAC addresses in its MAC table.
To begin to see the STP style of certain interface, use the show spanning-tree interface command.
SW1#show spanning-tree software rapidly 0/11
Vlan Role Sts Cost Prio.Nbr Kind
---- --- --------- -------- ----------
VLAN0001 Desg FWD 19 128.11 P2p
To see these states for action, shut a down in your CCNA / CCNP house laboratory and constantly run the show comprising software command. When you see this in action on real Cisco equipment, you'll don't have any problem with BCMSN exam questions. Just don't exercise this or every other Cisco command on a production system!
