Medianet Reference Guide - Cisco

Network Availability Technologies
Chapter 3
Medianet Availability Design Considerations
Figure 3-9
STP-Based Redundant Topology
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STP Blocked Link
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STP prevents a loop in the topology by transitioning all (STP-enabled) ports through four STP states:
• Blocking—The port does not participate in frame forwarding. STP can take up to 20 seconds (by
default) to transition a port from blocking to listening.
• Listening—The port transitional state after the blocking state when the spanning tree determines
that the interface should participate in frame forwarding. STP takes 15 seconds (by default) to
transition between listening and learning.
• Learning—The port prepares to participate in frame forwarding. STP takes 15 seconds (by default)
to transition from learning to forwarding (provided such a transition does not cause a loop;
otherwise, the port is be set to blocking).
• Forwarding—The port forwards frames.
Figure 3-10 illustrates the STP states, including the disabled state.
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Medianet Reference Guide
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