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Spanning Tree
CST Port Summary
Use the CST Port Summary page to view and configure the Common Spanning Tree (CST) settings for
each interface on the device. To configure CST settings for an interface and to view additional informa-
tion about the interface's role in the CST topology, select the interface to view or configure and click
Edit
.
To display the Spanning Tree CST Port Configuration/Status page, click
Switching
>
Spanning Tree
in the navigation pane, and then click the
CST Port
tab.
Figure 30. Spanning Tree CST Port Summary Page
Table 20. Spanning Tree CST Port Summary Fields
Field
Description
Interface
The port or link aggregation group (LAG) associated with the rest of the data in the row. When
configuring CST settings for an interface, this field identifies the interface being configured.
Port Role
The role of the port within the CST, which is one of the following:
Root – A port on the non-root bridge that has the least-cost path to the root bridge.
Designated – A port that has the least-cost path to the root bridge on its segment.
Alternate – A blocked port that has an alternate path to the root bridge.
Backup – A blocked port that has a redundant path to the same network segment as
another port on the bridge.
Master – The port on a bridge within an MST instance that links the MST instance to
other STP regions.
Disabled – The port is administratively disabled and is not part of the spanning tree.
Port Forwarding State
Blocking – The port discards user traffic and receives, but does not send, BPDUs. During
the election process, all ports are in the blocking state. The port is blocked to prevent
network loops.
Listening – The port sends and receives BPDUs and evaluates information to provide a
loop-free topology. This state occurs during network convergence and is the first state in
transitioning to the forwarding state.
Learning – The port learns the MAC addresses of frames it receives and begins to popu-
late the MAC address table. This state occurs during network convergence and is the
second state in transitioning to the forwarding state.
Forwarding – The port sends and receives user traffic.
Disabled – The port is administratively disabled and is not part of the spanning tree.
