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From Sandbox Battle
As a CCNP candidate and a CCNA, you could be tempted to skip or just browse the numerous specifics of Spanning Tree Protocol. Following all, you discovered all of that in your CCNA studies, proper? That is appropriate, but it by no means hurts to assessment STP for a switching exam! Apart from, a lot of of us consider of the 4 STP port states - but officially, there's a fifth 1!
Disabled isn't typically thought of as an STP port state, but Cisco does officially think about this to be an STP state. A disabled port is one that is administratively shut down.
Once the port is opened, the port will go into blocking state. As the name implies, the port can not do a lot in this state - no frame forwarding, no frame receiving, and consequently no learning of MAC addresses. About the only factor this port can do is accept BPDUs from neighboring switches.
A port will then go from blocking mode into listening mode. The obvious query is "listening for what?" Listening for BPDUs - and this port can now send BPDUs as well. The port nevertheless can not forward or obtain information frames.
When the port goes from listening mode to understanding mode, it really is getting ready to send and receive frames. In understanding mode, the port begins to understand MAC addresses in preparation for adding them to its MAC address table.
Lastly, a port can go into forwarding mode. This allows a port to forward and receive data frames, send and receive BPDUs, and spot MAC addresses in its MAC table.
To see the STP mode of a given interface, use the show spanning-tree interface command.
SW1#show spanning-tree interface rapidly /11
Vlan Function Sts Price Prio.Nbr Kind
---- --- --------- -------- ----------
VLAN0001 Desg FWD 19 128.11 P2p
To see these states in action, shut a port down in your CCNA / CCNP house lab and continually run the show spanning interface command. Once you see this in action on true Cisco gear, you will have no difficulty with BCMSN exam queries. Just don't practice this or any other Cisco command on a production network! [ We're Listening To You]
