Learning State; Forwarding State; Disabled State; How A Switch Or Port Becomes The Root Switch Or Root Port - Cisco ME 3400 Software Configuration Manual

Chapter 14 Configuring STP

Learning State

A Layer 2 interface in the learning state prepares to participate in frame forwarding. The interface enters
the learning state from the listening state.
An interface in the learning state performs these functions:
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Forwarding State

A Layer 2 interface in the forwarding state forwards frames. The interface enters the forwarding state
from the learning state.
An interface in the forwarding state performs these functions:
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Disabled State

A Layer 2 interface in the disabled state does not participate in frame forwarding or in the spanning tree.
An interface in the disabled state is nonoperational.
A disabled interface performs these functions:
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How a Switch or Port Becomes the Root Switch or Root Port

If all switches in a network are enabled with default spanning-tree settings, the switch with the lowest
MAC address becomes the root switch. In
the switch priority of all the switches is set to the default (32768) and Switch A has the lowest MAC
address. However, because of traffic patterns, number of forwarding interfaces, or link types, Switch A
might not be the ideal root switch. By increasing the priority (lowering the numerical value) of the ideal
switch so that it becomes the root switch, you force a spanning-tree recalculation to form a new topology
with the ideal switch as the root.
OL-9639-07
Discards frames received on the interface
Discards frames switched from another interface for forwarding
Learns addresses
Receives BPDUs
Receives and forwards frames received on the interface
Forwards frames switched from another interface
Learns addresses
Receives BPDUs
Discards frames received on the interface
Discards frames switched from another interface for forwarding
Does not learn addresses
Does not receive BPDUs
Figure 14-2, Switch A is elected as the root switch because
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
Understanding Spanning-Tree Features
14-7