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Foundry NetIron M2404C and M2404F Metro Access Switches
Configuring STP (Rev. 03)
Spanning Tree Protocol (STP)
© 2008 Foundry Networks, Inc.
Page 9 of 38
Figure 3: Example for Calculating the Diameter
The user can see from the diagram that there is no pair of devices that would give a diameter
higher than five.
STP Port States
Propagation delays can occur when protocol information passes through a switched LAN. As a
result, topology changes can take place at different times and at different places in a switched
network. When a port transitions directly from nonparticipation in the spanning-tree topology to
the forwarding state, it can create temporary data loops. Ports must wait for new topology
information to propagate through the switched LAN before starting to forward frames. They must
allow the frame lifetime to expire for forwarded frames that have used the old topology.
Each port on a switch using STP exists in one of these states:
•
Blocking
- The port does not participate in frame forwarding
•
Listening
- the first transitional state after the blocking state when STP determines that the
port should participate in frame forwarding
•
Learning
- The port prepares to participate in frame forwarding
•
Forwarding
- The port forwards frames
•
Disabled
- The port is not participating in STP because of a shutdown port, no link on the port,
or no spanning-tree instance running on the port.
A port moves through these states:
•
From initialization 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.
Table 4
illustrates how a port moves through the states.