3Com 3CBLUG16A User Guide - Page 45

Spanning Tree, Bridge generates BPDUs Bridge Protocol Data Units

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lost while the new software is being copied to the Switch). The upgrade procedure can take a few minutes, and is complete when the Power LED has stopped flashing and is permanently green. Make sure that you do not interrupt power to the Switch during the upgrade procedure; if you do, the software may be corrupted and the Switch may not start up properly afterwards. If the Power LED continues to flash after a failed upgrade, refer to "Troubleshooting" on page 49. Spanning Tree This administrative tool supports the configuration of the Switch to forward, or block and discard 802.1D spanning tree BPDU packets. Spanning tree is a bridge-based system for providing fault tolerance on networks and can be used to detect and disable network loops. The spanning tree ensures that the optimal path is maintained between spanning tree-compliant networked devices by: ■ Disabling redundant paths when the main paths are operational. ■ Enabling redundant paths if the main paths fail. Spanning tree uses a distributed algorithm to select a bridging device that serves as the root of the spanning tree network. The bridging device known as the Root Bridge generates BPDUs (Bridge Protocol Data Units) on all ports at a regular interval known as the Hello Time. Using the System Tools 45 All other spanning tree-compliant devices on the network have a designated Root Port. This is the Port nearest the Root Bridge and it is used for receiving the BPDUs initiated by the Root Bridge. If a bridge does not get a Hello BPDU after a predetermined interval, the bridge assumes that the link to the Root Bridge is down. This bridge will then initiate negotiations with other bridges to reconfigure the network to reestablish a valid network topology. After all the bridges on the network have determined the configuration of their ports, each bridge only forwards traffic between the Root Port and the ports that are the Designated Bridge Ports for each network segment. All other ports are blocked, which means that they are prevented from forwarding traffic.

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Using the System Tools
45
lost while the new software is being copied to the
Switch).
The upgrade procedure can take a few minutes, and is
complete when the Power LED has stopped flashing and
is permanently green. Make sure that you do not inter-
rupt power to the Switch during the upgrade proce-
dure; if you do, the software may be corrupted and the
Switch may not start up properly afterwards. If the
Power LED continues to flash after a failed upgrade,
refer to “Troubleshooting” on page 49.
Spanning Tree
This administrative tool supports the configuration of
the Switch to forward, or block and discard 802.1D
spanning tree BPDU packets.
Spanning tree is a bridge-based system for providing
fault tolerance on networks and can be used to detect
and disable network loops. The spanning tree ensures
that the optimal path is maintained between spanning
tree-compliant networked devices by:
■
Disabling redundant paths when the main paths are
operational.
■
Enabling redundant paths if the main paths fail.
Spanning tree uses a distributed algorithm to select a
bridging device that serves as the root of the spanning
tree network. The bridging device known as the Root
Bridge generates BPDUs (Bridge Protocol Data Units) on
all ports at a regular interval known as the Hello Time.
All other spanning tree-compliant devices on the
network have a designated Root Port. This is the Port
nearest the Root Bridge and it is used for receiving the
BPDUs initiated by the Root Bridge. If a bridge does not
get a Hello BPDU after a predetermined interval, the
bridge assumes that the link to the Root Bridge is down.
This bridge will then initiate negotiations with other
bridges to reconfigure the network to reestablish a valid
network topology.
After all the bridges on the network have determined
the configuration of their ports, each bridge only
forwards traffic between the Root Port and the ports
that are the Designated Bridge Ports for each network
segment. All other ports are blocked, which means that
they are prevented from forwarding traffic.