24-port NWay Ethernet Switch User’s Guide
46
Switch Management and Operating Concepts
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
A port transitions from one state to another as follows:
??
From initialization (switch boot) to blocking
??
From blocking to listening or to disabled
??
From listening to learning or to disabled
??
From learning to forwarding or to disabled
??
From forwarding to disabled
??
From disabled to blocking
