Cisco Systems 3130 사용자 설명서
17-6
Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
OL-13270-01
Chapter 17 Configuring STP
Understanding Spanning-Tree Features
•
From learning to forwarding or to disabled
•
From forwarding to disabled
illustrates how an interface moves through the states.
Figure 17-2
Spanning-Tree Interface States
When you power up the switch, spanning tree is enabled by default, and every interface in the switch,
VLAN, or network goes through the blocking state and the transitory states of listening and learning.
Spanning tree stabilizes each interface at the forwarding or blocking state.
VLAN, or network goes through the blocking state and the transitory states of listening and learning.
Spanning tree stabilizes each interface at the forwarding or blocking state.
When the spanning-tree algorithm places a Layer 2 interface in the forwarding state, this process occurs:
1.
The interface is in the listening state while spanning tree waits for protocol information to move the
interface to the blocking state.
interface to the blocking state.
2.
While spanning tree waits the forward-delay timer to expire, it moves the interface to the learning
state and resets the forward-delay timer.
state and resets the forward-delay timer.
3.
In the learning state, the interface continues to block frame forwarding as the switch learns
end-station location information for the forwarding database.
end-station location information for the forwarding database.
4.
When the forward-delay timer expires, spanning tree moves the interface to the forwarding state,
where both learning and frame forwarding are enabled.
where both learning and frame forwarding are enabled.
Blocking State
A Layer 2 interface in the blocking state does not participate in frame forwarding. After initialization, a
BPDU is sent to each switch interface. A switch initially functions as the root until it exchanges BPDUs
with other switches. This exchange establishes which switch in the network is the root or root switch. If
there is only one switch in the network, no exchange occurs, the forward-delay timer expires, and the
interface moves to the listening state. An interface always enters the blocking state after switch
initialization.
BPDU is sent to each switch interface. A switch initially functions as the root until it exchanges BPDUs
with other switches. This exchange establishes which switch in the network is the root or root switch. If
there is only one switch in the network, no exchange occurs, the forward-delay timer expires, and the
interface moves to the listening state. An interface always enters the blocking state after switch
initialization.
An interface in the blocking state performs these functions:
•
Discards frames received on the interface
•
Discards frames switched from another interface for forwarding
Power-on
initialization
Blocking
state
4
3569
Listening
state
Disabled
state
Learning
state
Forwarding
state