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From Patristics In English Project
As a CCNP candidate and a CCNA, you may possibly be tempted to skip or just browse the many particulars of Spanning Tree Protocol. After all, you learned all of that in your CCNA studies, right? That's appropriate, but it never hurts to evaluation STP for a switching exam! In addition to, many of us feel of the 4 STP port states - but officially, there is a fifth one!
Disabled is not generally thought of as an STP port state, but Cisco does officially take into account this to be an STP state. A disabled port is a single that is administratively shut down.
After the port is opened, the port will go into blocking state. As the name implies, the port can't do a lot in this state - no frame forwarding, no frame receiving, and for that reason no studying of MAC addresses. About the only thing this port can do is accept BPDUs from neighboring switches.
A port will then go from blocking mode into listening mode. The clear question is "listening for what?" Listening for BPDUs - and this port can now send BPDUs as nicely. The port nevertheless cannot forward or acquire information frames.
When the port goes from listening mode to studying mode, it really is getting prepared to send and obtain frames. In learning mode, the port begins to understand MAC addresses in preparation for adding them to its MAC address table.
Ultimately, a port can go into forwarding mode. This permits a port to forward and receive data frames, send and acquire 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 quickly /11
Vlan Function Sts Cost 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 real Cisco gear, you will have no difficulty with BCMSN exam queries. Just never practice this or any other Cisco command on a production network! [ Article Directory]
