States
Port States
Blocking
Only receives
No
No
Stable
Listening
Sends and receives
No
No
Transitional
Learning
Sends and receives
No
Yes
Transitional
Forwarding
Sends and receives
Yes
Yes
Stable
Disabled
Does not send or receive
No
No
Stable
Root/Designated ports remain stable in a Forwarding state.
Non-designated ports remain stable in a Blocking state.
Listening and Learning are transitional states which are passed through when an interface is activated, or when a Blocking port must transition to a Forwarding state due to a change in the network topology.
Blocking
Non-designated ports are in a Blocking state.
Interfaces in a Blocking state...
... are effectively disabled to prevent loops.
... do not send/receive regular network traffic.
... receive STP BPDUs.
... do not forward BPDUs.
... do not learn MAC addresses.
Listening
After the Blocking state, interfaces with the Designated or Root role enter the Listening state.
Only Designated or Root ports enter the Listening state (Non-designated ports are always Blocking).
The Listening state is 15 seconds long by default. This is determined by the Forward delay timer.
An interface in the Listening state...
... only forwards/receives STP BPDUs.
... does not send/receive regular traffic.
... does not learn MAC addresses from regular traffic that arrives on the interface.
Learning
After the Listening state, a Designated or Root port will enter the Learning state.
The Learning state is 15 seconds long by default. This is determined by the Forward delay timer (the same timer is used for both the Listening and Learning states).
An interface in the Learning state...
... only sends/receives STP BPDUs.
... does not send/receive regular traffic.
... learns MAC addresses from regular traffic that arrives on the interface.
Forwarding
Root and Designated ports are in a Forwarding state.
A port in the Forwarding state...
... operates as normal.
... sends/receives BPDUs.
... sends/receives normal traffic.
... learns MAC addresses.
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