Blocking State - Cisco nexus 5000 series Configuration Manual

Configuring Rapid PVST+
When the STP algorithm places a LAN port in the forwarding state, the following process occurs:
• The LAN port is put into the blocking state while it waits for protocol information that suggests it should
go to the learning state.
• The LAN port waits for the forward delay timer to expire, moves the LAN port to the learning state, and
restarts the forward delay timer.
• In the learning state, the LAN port continues to block frame forwarding as it learns the end station
location information for the forwarding database.
• The LAN port waits for the forward delay timer to expire and then moves the LAN port to the forwarding
state, where both learning and frame forwarding are enabled.

Blocking State

A LAN port in the blocking state does not participate in frame forwarding.
A LAN port in the blocking state performs as follows:
• Discards frames received from the attached segment.
• Discards frames switched from another port for forwarding.
• Does not incorporate the end station location into its address database. (There is no learning on a blocking
LAN port, so there is no address database update.)
• Receives BPDUs and directs them to the system module.
• Receives, processes, and transmits BPDUs received from the system module.
• Receives and responds to network management messages.
Learning State
A LAN port in the learning state prepares to participate in frame forwarding by learning the MAC addresses
for the frames. The LAN port enters the learning state from the blocking state.
A LAN port in the learning state performs as follows:
• Discards frames received from the attached segment.
• Discards frames switched from another port for forwarding.
• Incorporates the end station location into its address database.
• Receives BPDUs and directs them to the system module.
• Receives, processes, and transmits BPDUs received from the system module.
• Receives and responds to network management messages.
Forwarding State
A LAN port in the forwarding state forwards frames. The LAN port enters the forwarding state from the
learning state.
A LAN port in the forwarding state performs as follows:
OL-25842-01
Cisco Nexus 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.1(3)N1(1)
Understanding Rapid PVST+
171