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3.5.2. Port States and Roles
Rapid PVST+ Port States:
| State | Learning? | Forwarding? | Duration |
|---|---|---|---|
| Discarding | No | No | Varies |
| Learning | Yes | No | Skipped on a point-to-point link; up to 15s forward delay only as a fallback |
| Forwarding | Yes | Yes | Stable state |
RSTP's discarding state replaces three 802.1D states (disabled, blocking and listening), none of which learns MACs or forwards frames.
Port Roles:
| Role | Description |
|---|---|
| Root Port | Best path to root (one per non-root switch) |
| Designated Port | Forwards traffic on segment toward root |
| Alternate Port | Backup to root port (blocked) |
| Backup Port | Backup to designated port on same switch (rare) |
In show spanning-tree interface <if> detail, a climbing Number of transitions to forwarding state means the port keeps losing and regaining its role: a flapping link or repeated topology changes worth investigating.
Rapid PVST+ State Transitions:
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Written byAlvin Varughese
Founder•20 professional certifications