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Difficulty: MediumSpanning Tree Protocol Operations

A network administrator connects several new switches in a redundant topology to ensure high availability. Place the steps of the initial IEEE 802.1D Spanning Tree Protocol (STP) convergence process in the correct chronological order from link startup to topology stabilization.

  1. 1Switches boot up and transmit Bridge Protocol Data Units (BPDUs) claiming themselves as the Root Bridge.
  2. 2Switches process received BPDUs and elect the single switch with the lowest Bridge ID as the Root Bridge.
  3. 3Each non-root switch evaluates path costs and selects one Root Port offering the shortest path to the Root Bridge.
  4. 4Switches elect a single Designated Port for each network segment based on the lowest root path cost.
  5. 5All remaining switch ports that are neither Root Ports nor Designated Ports transition to the Blocking state.

Answer

The correct chronological order of IEEE 802.1D STP convergence is: 1) Switches originate BPDUs claiming to be the Root Bridge, 2) The switch with the lowest Bridge ID is elected as the Root Bridge, 3) Non-root switches elect their Root Ports, 4) Segment-level Designated Ports are elected, and 5) Remaining redundant ports enter the Blocking state.
The standard IEEE 802.1D STP algorithm operates sequentially: switches announce themselves as root via initial BPDUs, elect the true Root Bridge based on the lowest Bridge ID, select Root Ports on non-root switches, designate single forwarding ports per segment, and block remaining redundant links to eliminate loops.

Step-by-Step Solution

1
Identify initial BPDU transmission upon boot.
Switches send initial BPDUs asserting Root Bridge status.
Before exchanging information, switches lack topology visibility and default to claiming root status.
2
Complete Root Bridge election process.
The switch with the lowest Bridge Priority (or lowest MAC address as tiebreaker) becomes the agreed Root Bridge.
BPDUs with superior (lower) Bridge IDs override inferior claims across the broadcast domain.
3
Select non-root switch Root Ports.
Each non-root switch assigns its port with the lowest Root Path Cost as its Root Port.
Non-root switches require exactly one active path to send traffic toward the Root Bridge.
4
Elect segment-level Designated Ports.
The switch port on each segment with the lowest cost to the Root Bridge becomes the Designated Port.
Each LAN segment must have one designated forwarding interface to prevent loop formation.
5
Place unassigned redundant ports into Blocking state.
All non-root, non-designated ports transition to Blocking.
Ports not assigned active forwarding roles must block data traffic to eliminate physical switching loops.

Key Concept

Spanning Tree Protocol Convergence Sequence
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Topics

Spanning Tree Protocol Operations

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