3Com CoreBuilder 3500, Руководство по внедрению

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How the Spanning Tree Protocol Works 129
Spanning Tree
Port States
Because STP determines the network configuration or adjusts it,
depending on events that occur, it places bridge ports in one of the
following states at all times: listening, learning, forwarding, blocking, or
disabled. Table 12 describes these states.
Table 12 Spanning Tree Protocol Port States
Port State Description
Listening When STP is configuring, all ports are placed in the listening state.
Each port remains in this state until the root bridge is elected. While
in the listening state, the bridge continues to run STP and to transmit
CBPDUs on the port; however, the bridge discards data packets that
are received on that port and does not transmit data packets from
that port.
The listening state should be long enough for a bridge to hear
from all other bridges on the network. After being in the listening
state, the bridge ports that are to proceed to the forwarding state
go into the learning state. All other bridge ports go into the
blocking state.
Learning The learning state is similar to the listening state except that data
packets are received on that port for the purpose of learning which
stations are attached to that port. After spending the specified time
in this state without receiving information to change the port back
to the blocking state, the bridge changes the port to the forwarding
state.
The time that the port spends in each of the listening and learning
states is determined by the value of the
forward delay parameter.
Forwarding After the port enters the forwarding state, the bridge performs
standard bridging functions.
Blocking When a port is put in the blocking state, the bridge continues to
receive CBPDUs on that port (monitoring for network
reconfigurations), but it does not transmit them. In addition, the
bridge does not receive data packets from the port, learn the
locations of station addresses from it, or forward packets onto it.
Disabled A port is disabled when the STP has been disabled on the port or
when the port has failed. In the disabled state, the port does not
participate in the Spanning Tree algorithm. The port continues to
forward frames only if STP is disabled for the entire bridge and the
link is up.