---
id: 1778913634-WEMK
aliases:
  - Protocole Spanning Tree (part2)
tags: []
---

# Protocole Spanning Tree (part2)

## Spanning Tree Port State

| STP Port State | Stable/Transitional |
| -------------- | --------------- |
| Blocking | Statble |
| Listening | Transitional |
| Learning | Transitional |
| Forwarding | Stable |
| Disabled |  Stable |

- Root/Designated ports remain stab;e in Forwarding state.
- Non-designated ports remain stabl in a Blocking state.
- Listening and Learning are transitional states which are passed through when an interface is 
activated, or when a *Blocking* port must transition to a Forwarding state due to a change in the
network topology

### Blocking state

- Non designated ports are in a Blocking state
- Interfaces in a Blocking state are effectively disabed to prevent loops.
- Interfaces in a Blocking stae do not send/receive regular naetwork traffic.
- Interfaces in a Blocking state receive STP BPDUs.
- Interfaces in a Blocing state do NOT forward STP BPDUs.
- Interfaces in a Blocking state do NOT learn [[MAC]] addresses.

### Listening state

- After the Blocking state interfaces with the Designated or Root role enter Listening state.
- Only Designated or Root ports enter the Listening state (Non-designated ports are always Blocking)
- The Listening state is 15 seconds long by default. This is determined by the *orward delay* timer.
- An interface in the listening state ONLY forwards/receives STP BPDUs.
- An interface in the Listening state does NOT send/receive regular traffic
- An interface in the Listening state does NOT Learn MAC addresses from regular traffic that
arrives on the interface

### Learning state

- After the Listeing state, a Designated or ROOT port will enter Learning state.
- The Learning state is 15 seconds long by default. This is determined by the Forward delay
timer ( the same timer is used for both the Listening and Learning states).
- An interface in the Learning state ONLY sends/receives STP BPDUs.
- An interface in the Learning state learns MAC addresses from regular traffic that arrives on
the interface.

### Forwarding state

- Root and designated ports are in a Forwarding state.
- A port in the Forwarding state operate as normal
- A port in the Forwarding state sends/receives BPDUs.
- A port in the Forwarding state sends/receives normal traffic.
- A port in the Forwarding state learns MAC addresses.

### summary


| STP Port State |Send/Receive BPDUs | Frame forwarding | Mac address learning| Stable/Transitional |
| -------------- |----|----|----| --------------- |
| Blocking | No/Yes|   NO | NO  | Statble |
| Listening | Yes/Yes|   NO | NO  | Transitional |
| Learning | Yes/Yes|   NO | Yes  | Transitional |
| Forwarding | Yes/Yes|   Yes | Yes  | Stable |
| Disabled | NO/NO|   NO | NO  | Stable |


    note: Switches do not forward the BPDUs out of their root ports and non-designated ports,
    only their designated ports

## STP timers

### Hello

How often the root bridge sends hello BPDUs
duration: 2 sec

### Forward delay

How long the switch will stay in the Listening and Learning states (each stae is 15 seconds 
= total 30 seconds)
duration: 15sec

### Max Age

How long an interface will wait after ceasing to receive Hello BDPUs to change the STP topology
duration: 20 sec (10*hello)

- If another BPDU i received before the max age timer counts down to 0, the time will reset to 20 
seconds and no changes will ocur.

- If another BPDU is not received the max age timer counts down to 0 and the switch will
reevaluate its STP choices, including root bridge, and local root, designated, and non-designated ports

- if a non-designated port is selected to become a designated or root port, it will transition 
from the blocking state to the listening state (15 seconds), learning state (15 seconds),
and then finally the forwarding state. So it can take a total of 50 seconds for a blocking
interface to transition to forwarding

## Review

- STP state/timers
- STP BPDU
- STP optional features
- STP configuration