User manual

(Rapid) Spanning Tree
6874_en_09 PHOENIX CONTACT 5-13
The properties of the various port states are shown in the table below.
The sequence of the five port states defined in the Spanning Tree Protocol cannot be
assigned freely. The following diagram illustrates the possible sequence of the port states.
Figure 5-11 Sequence of the possible port states in STP
After device startup and, if necessary, also during topology modification, a port passes
through the states in the following order:
Learning → Forwarding
Or
Disabled → Blocking/Discarding
Due to the edge property of ports, they switch to "Forwarding" immediately. In the second
case, the port generates a data path interruption in order to suppress loops accordingly.
5.2.4.3 Fast Forwarding
If the Spanning Tree Protocol is deactivated at a port, the corresponding port is in "Fast
Forwarding" mode.
A fast forwarding port:
– Ignores all BPDUs that are received at this port.
– Does not send any BPDUs.
Table 5-1 Properties of the port states
Receiving and Evaluating
BPDUs (Learning the
Topology)
Learning the MAC
Addresses of Connected
Devices and Creating
Switching Tables
Forwarding Data Packets
(Normal Switching Function)
Disabled
Blocking/Discarding X
Learning XX
Forwarding XX X
At least one port in the "Forwarding" state is at a data path between two Spanning Tree
switches so that the data path can be integrated into the network.
Forwarding
Blocking
Disabled
Learning
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