• Arista Spanning Tree User Manual : Docs

• Spanning Tree GFG : Article on GFG

• PPT made by me on Canva : PPT

Bridge Protocol Data Units (BPDUs) are essential frames exchanged between switches in a network to manage the Spanning Tree Protocol (STP). BPDUs are responsible for maintaining the network topology by helping switches identify the root bridge, select port roles, and detect loops. There are two main types of BPDUs:

1. Configuration BPDUs: Used to identify the root bridge and to maintain topology information by exchanging details like bridge IDs and root path costs.

2. Topology Change Notification (TCN) BPDUs: Sent by a switch when a topology change occurs, such as when a device is added or removed.

BPDUs are exchanged regularly between switches, ensuring that the network topology remains stable, loop-free, and efficient. Without BPDUs, STP wouldn't be able to function effectively, leading to potential network loops and inefficiencies.

In Spanning Tree Protocol (STP), each switch port plays a specific role based on its function within the network topology. The port roles help prevent network loops while maintaining optimal path selection. The key port roles in STP are:

1. Root Port:

   • This port has the best path to the root bridge. Each switch (except the root bridge itself) has one root port, and it's used to forward traffic towards the root bridge.

2. Designated Port:

   • The designated port on a segment is responsible for forwarding traffic away from the root bridge. Each network segment has one designated port, typically on the switch closest to the root bridge.

3. Alternate Port:

   • An alternate path to the root bridge that is in a blocking state. It steps in to take over if the root port fails.

4. Backup Port:

   • A backup path to the designated port within the same network segment. It is also in a blocking state unless the designated port fails.

5. Disabled Port:

   • A port that is administratively shut down and does not participate in the STP process.

These roles ensure that traffic flows efficiently, preventing network loops and maintaining stability in the network.

Port activity status refers to the operational state of a network port at a given time. In networking, a port can have several activity statuses depending on its configuration and the role it plays in protocols like Spanning Tree Protocol (STP). The common port activity statuses are:

1. Forwarding:

   • The port is actively passing traffic (both user data and BPDU packets in case of STP). This is the normal operating state for a port that is part of the active topology.

2. Blocking:

   • The port is not forwarding traffic to prevent loops in the network. However, it may still receive and process BPDU packets in protocols like STP.

3. Listening:

   • The port is not forwarding traffic but is preparing to transition to a forwarding or blocking state. It listens for BPDU packets to determine the network topology.

4. Learning:

   • The port is not forwarding user traffic yet, but it is learning MAC addresses to build the switch's MAC address table, so it can prepare to forward traffic efficiently.

5. Disabled:

   • The port is administratively or operationally disabled and does not participate in network operations.

6. Discarding:

   • The port discards all incoming frames, used in advanced STP enhancements like Rapid STP (RSTP).

These statuses are essential for managing the flow of network traffic and preventing issues like network loops.

n Spanning Tree Protocol (STP), bridge timers are crucial for controlling the convergence process, ensuring the network stabilizes after topology changes. The primary bridge timers are:

1. Hello Time:

   • This is the interval at which the Root Bridge sends BPDU (Bridge Protocol Data Units) packets to other switches in the network. The default hello time is 2 seconds, and it helps in maintaining communication and ensuring the network topology remains updated.

2. Forward Delay:

   • Forward delay is the time spent by a port in both the Listening and Learning states before transitioning to the Forwarding or Blocking state. By default, this time is 15 seconds. The delay ensures that the network avoids temporary loops by allowing switches to learn the topology before forwarding traffic.

3. Max Age:

   • Max Age defines how long a switch retains the BPDU information it receives before discarding it, assuming no new BPDUs are received. The default value is 20 seconds. If a switch doesn’t hear from the Root Bridge within this time frame, it initiates a re-calculation of the network topology.

These timers are configurable but should be adjusted carefully to avoid network instability or convergence delays.