Stp Port States - Enterasys VH-2402-L3 Management Manual

When STP is enabled using the default parameters, the path
between source and destination stations in a switched
network might not be ideal. For instance, connecting higher-
speed links to a port that has a higher number than the
current root port can cause a root-port change. The goal is
to make the fastest link the root port.

STP Port States

The BPDUs take some time to pass through a network. This
propagation delay can result in topology changes where a
port that transitioned directly from a Blocking state to a
Forwarding state could create temporary data loops. Ports
must wait for new network topology information to propagate
throughout the network before starting to forward packets.
They must also wait for the packet lifetime to expire for
BPDU packets that were forwarded based on the old
topology. The forward delay timer is used to allow the
network topology to stabilize after a topology change.
In addition, STP specifies a series of states a port must
transition through to further ensure that a stable network
topology is created after a topology change.
Each port on a switch using STP exists is in one of the
following five states:
•
Blocking – the port is blocked from forwarding or receiving
packets
•
Listening – the port is waiting to receive BPDU packets that
may tell the port to go back to the blocking state
•
Learning – the port is adding addresses to its forwarding
database, but not yet forwarding packets
•
Forwarding – the port is forwarding packets
•
Disabled – the port only responds to network management
messages and must return to the blocking state first
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