What determines which switch becomes the root bridge?
An election process determines which switch becomes the root bridge. Each switch has a Bridge ID (BID) that is made up of a priority value, an extended system ID, and the MAC address of the switch. All switches in the network take part in the election process. The root ID identifies the root bridge on the network.
How is the root port on a switch determined?
When determining the root port on a switch, the switch compares the path costs on all switch ports participating in the spanning tree. The switch port with the lowest overall path cost to the root bridge is automatically assigned the root port role because it is closest to the root bridge.
What is required for a switch to win the election to become the root switch?
Since the BID starts with the Bridge Priority field, essentially, the switch with the lowest Bridge Priority field becomes the Root Bridge. If there is a tie between two switches having the same priority value, then the switch with the lowest MAC address becomes the Root Bridge.
How are root switches elected?
The switch with the highest switch priority (the lowest numerical priority value) is elected as the root switch. If all of the switches are configured with the default priority (32768) for a VLAN with ID 1 (that is, a bridge priority of 32769), then the switch with the lowest MAC address becomes the root switch.
What is STP root?
The root bridge of the spanning tree is the bridge with the smallest (lowest) bridge ID. Each bridge has a configurable priority number and a MAC address; the bridge ID is the concatenation of the bridge priority and the MAC address. For example, the ID of a bridge with priority 32768 and MAC 0200.0000.
How to elect the root switch in STP?
Electing the Root Switch in STP The STP process works by default on Cisco switches and begins with the root switch election. The election is based on the bridge IDs (BIDs) sent in the BPDUs. Each switch that participates in STP will have a 8-byte switch ID that comprises of the following fields:
How does the STP process work on Cisco switches?
The STP process works by default on Cisco switches and begins with the root switch election. The election is based on the bridge IDs (BIDs) sent in the BPDUs. Each switch that participates in STP will have a 8-byte switch ID that comprises of the following fields: 2-byte priority field – by default, all switches have the priority of 32768.
How to determine which switch is elected as the root bridge?
Information on which switch is elected as the root bridge is accessible on the dashboard. Best practice dictates the root bridge to be the core of the network, this can be accomplished by manually setting the priority of the switch selected to be the root bridge.
How to determine the RSTP / STP root bridge on an Cisco Meraki switch?
Best practice dictates the root bridge to be the core of the network, this can be accomplished by manually setting the priority of the switch selected to be the root bridge. Information on enabling RSTP and setting the STP root bridge on a Cisco Meraki MS switch can be found in our Configuring Spanning Tree on Meraki Switches article.