IBM BladeCenter Management Module, Installation And User Manual

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The following illustration shows the actions that occur when a port is in the learning
state.
CPU
Port 2 Port 2
Port 1 Port 1
Forwarding
Database Forwarding
Database
BPDUs
BPDUs
BPDUs
Addresses
Addresses
Discard
Forwarding
Data
Packets Data
Packets
Data
Packets Data
Packets
Network
Management
Packets Network
Management
Packets
Network Segment Network Segment
Network Segment Network Segment
Switch
Fabric Switch
Fabric
Learning
Forwarding state
A port in the forwarding state forwards packets. The port enters the forwarding state
from the learning state when the forward delay timer expires.
When the spanning-tree algorithm determines that a port should be changed to the
forwarding state, the following occurs:
The port is put into the listening state, where it receives bridge protocol data units
(BPDUs) and passes them to the switch CPU. BPDU packets from the CPU are
processed. If no BPDUs are received, this indicates that the port should go to the
blocking state:
v The port waits for the expiration of the forward delay timer. It then moves to the
learning state.
v In the learning state, the port learns station location information from the source
address of packets and adds this information to its forwarding database.
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IBM BladeCenter 4-Port Gb Ethernet Switch Module: Installation and User’s Guide