3com 2816-SFP Plus (3C16485) Manual Do Utilizador
35
Spanning Tree
This administrative tool supports the configuration of the Switch
to forward, or block and discard 802.1D spanning tree BPDU
packets.
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:
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.
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.
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
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.
traffic.
Figure 26 Spanning Tree Screen
■
Forward — Spanning tree BPDU packets received on a port
are forwarded to all other ports.
are forwarded to all other ports.
■
Block and Discard — Spanning tree BPDUs received on a port
are dropped. The Switch does not forward BPDUs to other
ports.
are dropped. The Switch does not forward BPDUs to other
ports.
The Switch does not participate as a bridge node in the spanning
tree, it can only be configured to forward or block spanning tree
BPDUs. If the Switch is connected to other bridging devices, such
as switches, that are part of the spanning tree network, set the
Switch to "Forward." If the Switch is connected only to
workstations, it can be set to "Block and Discard."
tree, it can only be configured to forward or block spanning tree
BPDUs. If the Switch is connected to other bridging devices, such
as switches, that are part of the spanning tree network, set the
Switch to "Forward." If the Switch is connected only to
workstations, it can be set to "Block and Discard."